1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.8, https://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Embed with GNU</title> <meta name="description" content="Embed with GNU"> <meta name="keywords" content="Embed with GNU"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <meta name="viewport" content="width=device-width,initial-scale=1"> <link href="#Top" rel="start" title="Top"> <link href="#SEC_Contents" rel="contents" title="Table of Contents"> <link href="#Libgloss" rel="next" title="Libgloss"> <style type="text/css"> <!-- a.copiable-anchor {visibility: hidden; text-decoration: none; line-height: 0em} a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} span:hover a.copiable-anchor {visibility: visible} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <h1 class="settitle" align="center">Embed with GNU</h1> <p>Copyright (c) 1993, 1994, 1995 Cygnus Support </p> <p>Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. </p> <p>Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. </p> <p>Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. </p> <div class="top" id="Top"> <div class="header"> <p> Next: <a href="#Libgloss" accesskey="n" rel="next">Libgloss</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Embed-with-GNU"></span><h1 class="top">Embed with GNU</h1> <p><strong>Rough Draft</strong> </p> <p>The goal of this document is to gather all the information needed to port the GNU tools to a new embedded target in one place. This will duplicate some info found in the other manual for the GNU tools, but this should be all you’ll need. </p> <div class="Contents_element" id="SEC_Contents"> <h2 class="contents-heading">Table of Contents</h2> <div class="contents"> <ul class="no-bullet"> <li><a id="toc-Libgloss-1" href="#Libgloss">1 Libgloss</a> <ul class="no-bullet"> <li><a id="toc-Supported-Targets" href="#Supported-targets">1.1 Supported Targets</a> <ul class="no-bullet"> <li><a id="toc-Sparclite-Targets-Supported" href="#Sparclite">1.1.1 Sparclite Targets Supported</a></li> <li><a id="toc-Motorola-CPU32-Targets-supported" href="#CPU32">1.1.2 Motorola CPU32 Targets supported</a></li> <li><a id="toc-Mips-core-Targets-Supported" href="#Mips">1.1.3 Mips core Targets Supported</a></li> <li><a id="toc-PA_002dRISC-Targets-Supported" href="#PA_002dRISC">1.1.4 PA-RISC Targets Supported</a></li> </ul></li> <li><a id="toc-Configuring-and-building-libgloss_002e" href="#Building-libgloss">1.2 Configuring and building libgloss.</a></li> <li><a id="toc-Adding-Support-for-a-New-Board" href="#Board-support">1.3 Adding Support for a New Board</a></li> </ul></li> <li><a id="toc-Porting-GCC" href="#GCC">2 Porting GCC</a> <ul class="no-bullet"> <li><a id="toc-Compilation-passes" href="#Overview">2.1 Compilation passes</a></li> </ul></li> <li><a id="toc-Porting-newlib" href="#Libraries">3 Porting newlib</a> <ul class="no-bullet"> <li><a id="toc-Crt0_002c-the-main-startup-file" href="#Crt0">3.1 Crt0, the main startup file</a></li> <li><a id="toc-Linker-scripts-for-memory-management" href="#Linker-Scripts">3.2 Linker scripts for memory management</a></li> <li><a id="toc-What-to-do-when-you-have-a-binary-image" href="#What-to-do-now">3.3 What to do when you have a binary image</a></li> <li><a id="toc-Libraries-1" href="#Libc">3.4 Libraries</a> <ul class="no-bullet"> <li><a id="toc-Making-I_002fO-work" href="#I_002fO-Support">3.4.1 Making I/O work</a></li> <li><a id="toc-Routines-for-dynamic-memory-allocation" href="#Memory-Support">3.4.2 Routines for dynamic memory allocation</a></li> <li><a id="toc-Misc-support-routines" href="#Misc-Support">3.4.3 Misc support routines</a></li> <li><a id="toc-Useful-debugging-functions" href="#Debugging">3.4.4 Useful debugging functions</a></li> </ul></li> </ul></li> <li><a id="toc-Writing-a-new-GDB-backend" href="#GDB">4 Writing a new GDB backend</a> <ul class="no-bullet"> <li><a id="toc-The-standard-remote-protocol" href="#GNU-remote-protocol">4.1 The standard remote protocol</a></li> <li><a id="toc-A-linked-in-exception-handler" href="#Exception-handler">4.2 A linked in exception handler</a></li> <li><a id="toc-Using-a-ROM-monitor-as-a-backend" href="#ROM-monitors">4.3 Using a ROM monitor as a backend</a></li> <li><a id="toc-Adding-support-for-new-protocols" href="#Other-remote-protocols">4.4 Adding support for new protocols</a></li> </ul></li> <li><a id="toc-Code-Listings-1" href="#Code-Listings">Appendix A Code Listings</a> <ul class="no-bullet"> <li><a id="toc-Linker-script-for-the-IDP-board" href="#idp_002eld">A.1 Linker script for the IDP board</a></li> <li><a id="toc-crt0_002eS-_002d-The-startup-file" href="#crt0_002eS">A.2 crt0.S - The startup file</a></li> <li><a id="toc-C-based-_0022glue_0022-code_002e" href="#glue_002ec">A.3 C based "glue" code.</a></li> <li><a id="toc-I_002fO-assembler-code-sample" href="#mvme_002eS">A.4 I/O assembler code sample</a></li> <li><a id="toc-I_002fO-code-sample" href="#io_002ec">A.5 I/O code sample</a></li> <li><a id="toc-Led-control-sample" href="#leds_002ec">A.6 Led control sample</a></li> </ul></li> </ul> </div> </div> <hr> <div class="chapter" id="Libgloss"> <div class="header"> <p> Next: <a href="#GCC" accesskey="n" rel="next">Porting GCC</a>, Previous: <a href="#Top" accesskey="p" rel="prev">Embed with GNU</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Libgloss-1"></span><h2 class="chapter">1 Libgloss</h2> <p>Libgloss is a library for all the details that usually get glossed over. This library refers to things like startup code, and usually I/O support for <code>gcc</code> and <code>C library</code>. The C library used through out this manual is <code>newlib</code>. Newlib is a ANSI conforming C library developed by Cygnus Support. Libgloss could easily be made to support other C libraries, and it can be used standalone as well. The standalone configuration is typically used when bringing up new hardware, or on small systems. </p> <p>For a long time, these details were part of newlib. This approach worked well when a complete tool chain only had to support one system. A tool chain refers to the series of compiler passes required to produce a binary file that will run on an embedded system. For C, the passes are cpp, gcc, gas, ld. Cpp is the preprocessor, which process all the header files and macros. Gcc is the compiler, which produces assembler from the processed C files. Gas assembles the code into object files, and then ld combines the object files and binds the code to addresses and produces the final executable image. </p> <p>Most of the time a tool chain does only have to support one target execution environment. An example of this would be a tool chain for the AMD 29k processor family. All of the execution environments for this processor have the same interface, the same memory map, and the same I/O code. In this case all of the support code is under newlib/libc/sys. Libgloss’s creation was forced initially because of the <code>cpu32</code> processor family. There are many different execution environments for this line, and they vary wildly. newlib itself has only a few dependencies that it needs for each target. These are explained later in this doc. The hardware dependent part of newlib was reorganized into a separate directory structure within newlib called the stub dirs. It was initially called this because most of the routines newlib needs for a target were simple stubs that do nothing, but return a value to the application. They only exist so the linker can produce a final executable image. This work was done during the early part of 1993. </p> <p>After a while it became apparent that this approach of isolating the hardware and systems files together made sense. Around this same time the stub dirs were made to run standalone, mostly so it could also be used to support GDB’s remote debugging needs. At this time it was decided to move the stub dirs out of newlib and into it’s own separate library so it could be used standalone, and be included in various other GNU tools without having to bring in all of newlib, which is large. The new library is called Libgloss, for Gnu Low-level OS support. </p> <ul class="section-toc"> <li><a href="#Supported-targets" accesskey="1">Supported Targets</a></li> <li><a href="#Building-libgloss" accesskey="2">Configuring and building libgloss.</a></li> <li><a href="#Board-support" accesskey="3">Adding Support for a New Board</a></li> </ul> <hr> <div class="section" id="Supported-targets"> <div class="header"> <p> Next: <a href="#Building-libgloss" accesskey="n" rel="next">Configuring and building libgloss.</a>, Previous: <a href="#Libgloss" accesskey="p" rel="prev">Libgloss</a>, Up: <a href="#Libgloss" accesskey="u" rel="up">Libgloss</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Supported-Targets"></span><h3 class="section">1.1 Supported Targets</h3> <p>Currently libgloss is being used for the following targets: </p> <ul class="section-toc"> <li><a href="#Sparclite" accesskey="1">Sparclite Targets Supported</a></li> <li><a href="#CPU32" accesskey="2">Motorola CPU32 Targets supported</a></li> <li><a href="#Mips" accesskey="3">Mips core Targets Supported</a></li> <li><a href="#PA_002dRISC" accesskey="4">PA-RISC Targets Supported</a></li> </ul> <hr> <div class="subsection" id="Sparclite"> <div class="header"> <p> Next: <a href="#CPU32" accesskey="n" rel="next">Motorola CPU32 Targets supported</a>, Up: <a href="#Supported-targets" accesskey="u" rel="up">Supported Targets</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Sparclite-Targets-Supported"></span><h4 class="subsection">1.1.1 Sparclite Targets Supported</h4> <p>This is for the Fujitsu Sparclite family of processors. Currently this covers the ex930, ex931, ex932, ex933, and the ex934. In addition to the I/O code a startup file, this has a GDB debug-stub that gets linked into your application. This is an exception handler style debug stub. For more info, see the section on Porting GDB. <a href="#GDB">Porting GDB</a>. </p> <p>The Fujitsu eval boards use a host based terminal program to load and execute programs on the target. This program, <code>pciuh</code> is relatively new (in 1994) and it replaced the previous ROM monitor which had the shell in the ROM. GDB uses the the GDB remote protocol, the relevant source files from the gdb sources are remote-sparcl.c. The debug stub is part of libgloss and is called sparcl-stub.c. </p> <hr> </div> <div class="subsection" id="CPU32"> <div class="header"> <p> Next: <a href="#Mips" accesskey="n" rel="next">Mips core Targets Supported</a>, Previous: <a href="#Sparclite" accesskey="p" rel="prev">Sparclite Targets Supported</a>, Up: <a href="#Supported-targets" accesskey="u" rel="up">Supported Targets</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Motorola-CPU32-Targets-supported"></span><h4 class="subsection">1.1.2 Motorola CPU32 Targets supported</h4> <p>This refers to Motorola’s m68k based CPU32 processor family. The crt0.S startup file should be usable with any target environment, and it’s mostly just the I/O code and linker scripts that vary. Currently there is support for the Motorola MVME line of 6U VME boards and IDP line of eval boards. All of the Motorola VME boards run <code>Bug</code>, a ROM based debug monitor. This monitor has the feature of using user level traps to do I/O, so this code should be portable to other MVME boards with little if any change. The startup file also can remain unchanged. About the only thing that varies is the address for where the text section begins. This can be accomplished either in the linker script, or on the command line using the ‘<samp>-Ttext [address]</samp>’. </p> <p>There is also support for the <code>rom68k</code> monitor as shipped on Motorola’s IDP eval board line. This code should be portable across the range of CPU’s the board supports. There is also GDB support for this target environment in the GDB source tree. The relevant files are gdb/monitor.c, monitor.h, and rom58k-rom.c. The usage of these files is discussed in the GDB section. </p> <hr> </div> <div class="subsection" id="Mips"> <div class="header"> <p> Next: <a href="#PA_002dRISC" accesskey="n" rel="next">PA-RISC Targets Supported</a>, Previous: <a href="#CPU32" accesskey="p" rel="prev">Motorola CPU32 Targets supported</a>, Up: <a href="#Supported-targets" accesskey="u" rel="up">Supported Targets</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Mips-core-Targets-Supported"></span><h4 class="subsection">1.1.3 Mips core Targets Supported</h4> <p>The Crt0 startup file should run on any mips target that doesn’t require additional hardware initialization. The I/O code so far only supports a custom LSI33k based RAID disk controller board. It should easy to change to support the IDT line of eval boards. Currently the two debugging protocols supported by GDB for mips targets is IDT’s mips debug protocol, and a customized hybrid of the standard GDB remote protocol and GDB’s standard ROM monitor support. Included here is the debug stub for the hybrid monitor. This supports the LSI33k processor, and only has support for the GDB protocol commands <code>g</code>, <code>G</code>, <code>m</code>, <code>M</code>, which basically only supports the register and memory reading and writing commands. This is part of libgloss and is called lsi33k-stub.c. </p> <p>The crt0.S should also work on the IDT line of eval boards, but has only been run on the LSI33k for now. There is no I/O support for the IDT eval board at this time. The current I/O code is for a customized version of LSI’s <code>pmon</code> ROM monitor. This uses entry points into the monitor, and should easily port to other versions of the pmon monitor. Pmon is distributed in source by LSI. </p> <hr> </div> <div class="subsection" id="PA_002dRISC"> <div class="header"> <p> Previous: <a href="#Mips" accesskey="p" rel="prev">Mips core Targets Supported</a>, Up: <a href="#Supported-targets" accesskey="u" rel="up">Supported Targets</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="PA_002dRISC-Targets-Supported"></span><h4 class="subsection">1.1.4 PA-RISC Targets Supported</h4> <p>This supports the various boards manufactured by the HP-PRO consortium. This is a group of companies all making variations on the PA-RISC processor. Currently supported are ports to the WinBond ‘<samp>Cougar</samp>’ board based around their w89k version of the PA. Also supported is the Oki op50n processor. </p> <p>There is also included, but never built an unfinished port to the HP 743 board. This board is the main CPU board for the HP700 line of industrial computers. This target isn’t exactly an embedded system, in fact it’s really only designed to load and run HP-UX. Still, the crt0.S and I/O code are fully working. It is included mostly because their is a barely functioning exception handler GDB debug stub, and I hope somebody could use it. The other PRO targets all use GDB’s ability to talk to ROM monitors directly, so it doesn’t need a debug stub. There is also a utility that will produce a bootable file by HP’s ROM monitor. This is all included in the hopes somebody else will finish it. :-) </p> <p>Both the WinBond board and the Oki board download srecords. The WinBond board also has support for loading the SOM files as produced by the native compiler on HP-UX. WinBond supplies a set of DOS programs that will allow the loading of files via a bidirectional parallel port. This has never been tested with the output of GNU SOM, as this manual is mostly for Unix based systems. </p> <hr> </div> </div> <div class="section" id="Building-libgloss"> <div class="header"> <p> Next: <a href="#Board-support" accesskey="n" rel="next">Adding Support for a New Board</a>, Previous: <a href="#Supported-targets" accesskey="p" rel="prev">Supported Targets</a>, Up: <a href="#Libgloss" accesskey="u" rel="up">Libgloss</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Configuring-and-building-libgloss_002e"></span><h3 class="section">1.2 Configuring and building libgloss.</h3> <p>Libgloss uses an autoconf based script to configure. Autoconf scripts are portable shell scripts that are generated from a configure.in file. Configure input scripts are based themselves on m4. Most configure scripts run a series of tests to determine features the various supported features of the target. For features that can’t be determined by a feature test, a makefile fragment is merged in. The configure process leaves creates a Makefile in the build directory. For libgloss, there are only a few configure options of importance. These are –target and –srcdir. </p> <p>Typically libgloss is built in a separate tree just for objects. In this manner, it’s possible to have a single source tree, and multiple object trees. If you only need to configure for a single target environment, then you can configure in the source tree. The argument for –target is a config string. It’s usually safest to use the full canonical opposed to the target alias. So, to configure for a CPU32 (m68k) with a separate source tree, use: </p> <div class="example"> <pre class="example">../src/libgloss/configure --verbose --target m68k-coff </pre></div> <p>The configure script is in the source tree. When configure is invoked it will determine it’s own source tree, so the –srcdir is would be redundant here. </p> <p>Once libgloss is configured, <code>make</code> is sufficient to build it. The default values for <code>Makefiles</code> are typically correct for all supported systems. The test cases in the testsuite will also built automatically as opposed to a <code>make check</code>, where test binaries aren’t built till test time. This is mostly cause the libgloss testsuites are the last thing built when building the entire GNU source tree, so it’s a good test of all the other compilation passes. </p> <p>The default values for the Makefiles are set in the Makefile fragment merged in during configuration. This fragment typically has rules like </p> <div class="example"> <pre class="example">CC_FOR_TARGET = `if [ -f $${OBJROOT}/gcc/xgcc ] ; \ then echo ${OBJROOT}/gcc/xgcc -B${OBJROOT}/gcc/ ; \ else t='${program_transform_name}'; echo gcc | sed -e '' $$t ; fi` </pre></div> <p>Basically this is a runtime test to determine whether there are freshly built executables for the other main passes of the GNU tools. If there isn’t an executable built in the same object tree, then <em>transformed</em>the generic tool name (like gcc) is transformed to the name typically used in GNU cross compilers. The names are typically based on the target’s canonical name, so if you’ve configured for <code>m68k-coff</code> the transformed name is <code>m68k-coff-gcc</code> in this case. If you install with aliases or rename the tools, this won’t work, and it will always look for tools in the path. You can force the a different name to work by reconfiguring with the <code>--program-transform-name</code> option to configure. This option takes a sed script like this <code>-e s,^,m68k-coff-,</code> which produces tools using the standard names (at least here at Cygnus). </p> <p>The search for the other GNU development tools is exactly the same idea. This technique gets messier when build options like <code>-msoft-float</code> support are used. The Makefile fragments set the <code>MUTILIB</code> variable, and if it is set, the search path is modified. If the linking is done with an installed cross compiler, then none of this needs to be used. This is done so libgloss will build automatically with a fresh, and uninstalled object tree. It also makes it easier to debug the other tools using libgloss’s test suites. </p> <hr> </div> <div class="section" id="Board-support"> <div class="header"> <p> Previous: <a href="#Building-libgloss" accesskey="p" rel="prev">Configuring and building libgloss.</a>, Up: <a href="#Libgloss" accesskey="u" rel="up">Libgloss</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Adding-Support-for-a-New-Board"></span><h3 class="section">1.3 Adding Support for a New Board</h3> <p>This section explains how to add support for a new board to libgloss. In order to add support for a board, you must already have developed a toolchain for the target architecture. </p> <p>All of the changes you will make will be in the subdirectory named after the architecture used by your board. For example, if you are developing support for a new ColdFire board, you will modify files in the <samp>m68k</samp> subdirectory, as that subdirectory contains support for all 68K devices, including architecture variants like ColdFire. </p> <p>In general, you will be adding three components: a <samp>crt0.S</samp> file (see <a href="#Crt0">Crt0, the main startup file</a>), a linker script (see <a href="#Linker-Scripts">Linker scripts for memory management</a>), and a hardware support library. Each should be prefixed with the name of your board. For example, if you ard adding support for a new Surf board, then you will be adding the assembly <samp>surf-crt0.S</samp> (which will be assembled into <samp>surf-crt0.o</samp>), the linker script <samp>surf.ld</samp>, and other C and assembly files which will be combined into the hardware support library <samp>libsurf.a</samp>. </p> <p>You should modify <samp>Makefile.in</samp> to define new variables corresponding to your board. Although there is some variation between architectures, the general convention is to use the following format: </p> <div class="example"> <pre class="example"># The name of the crt0.o file. SURF_CRT0 = surf-crt0.o # The name of the linker script. SURF_SCRIPTS = surf.ld # The name of the hardware support library. SURF_BSP = libsurf.a # The object files that make up the hardware support library. SURF_OBJS = surf-file1.o surf-file2.o # The name of the Makefile target to use for installation. SURF_INSTALL = install-surf </pre></div> <p>Then, you should create the <code>${SURF_BSP}</code> and <code>${SURF_INSTALL}</code> make targets. Add <code>${SURF_CRT0}</code> to the dependencies for the <code>all</code> target and add <code>${SURF_INSTALL}</code> to the dependencies for the <code>install</code> target. Now, when libgloss is built and installed, support for your BSP will be installed as well. </p> <hr> </div> </div> <div class="chapter" id="GCC"> <div class="header"> <p> Next: <a href="#Libraries" accesskey="n" rel="next">Porting newlib</a>, Previous: <a href="#Libgloss" accesskey="p" rel="prev">Libgloss</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Porting-GCC"></span><h2 class="chapter">2 Porting GCC</h2> <p>Porting GCC requires two things, neither of which has anything to do with GCC. If GCC already supports a processor type, then all the work in porting GCC is really a linker issue. All GCC has to do is produce assembler output in the proper syntax. Most of the work is done by the linker, which is described elsewhere. </p> <p>Mostly all GCC does is format the command line for the linker pass. The command line for GCC is set in the various config subdirectories of gcc. The options of interest to us are <code>CPP_SPEC</code> and <code>STARTFILE_SPEC</code>. CPP_SPEC sets the builtin defines for your environment. If you support multiple environments with the same processor, then OS specific defines will need to be elsewhere. </p> <p><code>STARTFILE_SPEC</code> </p> <p>Once you have linker support, GCC will be able to produce a fully linked executable image. The only <em>part</em> of GCC that the linker wants is a crt0.o, and a memory map. If you plan on running any programs that do I/O of any kind, you’ll need to write support for the C library, which is described elsewhere. </p> <ul class="section-toc"> <li><a href="#Overview" accesskey="1">Compilation passes</a></li> </ul> <hr> <div class="section" id="Overview"> <div class="header"> <p> Next: <a href="#Options" accesskey="n" rel="next">Options</a>, Up: <a href="#GCC" accesskey="u" rel="up">Porting GCC</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Compilation-passes"></span><h3 class="section">2.1 Compilation passes</h3> <p>GCC by itself only compiles the C or C++ code into assembler. Typically GCC invokes all the passes required for you. These passes are cpp, cc1, gas, ld. <code>cpp</code> is the C preprocessor. This will merge in the include files, expand all macros definitions, and process all the <code>#ifdef</code> sections. To see the output of ccp, invoke gcc with the <code>-E</code> option, and the preprocessed file will be printed on the stdout. cc1 is the actual compiler pass that produces the assembler for the processed file. GCC is actually only a driver program for all the compiler passes. It will format command line options for the other passes. The usual command line GCC uses for the final link phase will have LD link in the startup code and additional libraries by default. </p> <p>GNU AS started it’s life to only function as a compiler pass, but these days it can also be used as a source level assembler. When used as a source level assembler, it has a companion assembler preprocessor called <code>gasp</code>. This has a syntax similar to most other assembler macros packages. GAS emits a relocatable object file from the assembler source. The object file contains the executable part of the application, and debug symbols. </p> <p>LD is responsible for resolving the addresses and symbols to something that will be fully self-contained. Some RTOS’s use relocatable object file formats like <code>a.out</code>, but more commonly the final image will only use absolute addresses for symbols. This enables code to be burned into PROMS as well. Although LD can produce an executable image, there is usually a hidden object file called <code>crt0.o</code> that is required as startup code. With this startup code and a memory map, the executable image will actually run on the target environment. <a href="#Crt0">Startup Files</a>. </p> <p>The startup code usually defines a special symbol like <code>_start</code> that is the default base address for the application, and the first symbol in the executable image. If you plan to use any routines from the standard C library, you’ll also need to implement the functions that this library is dependent on. <a href="#Libraries">Porting Newlib</a>. </p> <hr> <span id="Options"></span><div class="header"> <p> Previous: <a href="#Overview" accesskey="p" rel="prev">Compilation passes</a>, Up: <a href="#GCC" accesskey="u" rel="up">Porting GCC</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <h4 class="node-heading">Options</h4> <p>Options for the various development tools are covered in more detail elsewhere. Still, the amount of options can be an overwhelming amount of stuff, so the options most suited to embedded systems are summarized here. If you use GCC as the main driver for all the passes, most of the linker options can be passed directly to the compiler. There are also GCC options that control how the GCC driver formats the command line arguments for the linker. </p> <hr> <span id="GCC-Options"></span><div class="header"> <p> Next: <a href="#GAS-Options" accesskey="n" rel="next">GAS Options</a>, Up: <a href="#Options" accesskey="u" rel="up">Options</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <h4 class="node-heading">GCC Options</h4> <p>Most of the GCC options that we’re interested control how the GCC driver formats the options for the linker pass. </p> <dl compact="compact"> <dt><span><code>-nostartfiles</code></span></dt> <dt><span><code>-nostdlib</code></span></dt> <dt><span><code>-Xlinker</code></span></dt> <dd><p>Pass the next option directly to the linker. </p> </dd> <dt><span><code>-v</code></span></dt> <dt><span><code>-fpic</code></span></dt> </dl> <hr> <span id="GAS-Options"></span><div class="header"> <p> Next: <a href="#LD-Options" accesskey="n" rel="next">LD Options</a>, Previous: <a href="#GCC-Options" accesskey="p" rel="prev">GCC Options</a>, Up: <a href="#Options" accesskey="u" rel="up">Options</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <h4 class="node-heading">GAS Options</h4> <hr> <span id="LD-Options"></span><div class="header"> <p> Previous: <a href="#GAS-Options" accesskey="p" rel="prev">GAS Options</a>, Up: <a href="#Options" accesskey="u" rel="up">Options</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <h4 class="node-heading">LD Options</h4> <hr> </div> </div> <div class="chapter" id="Libraries"> <div class="header"> <p> Next: <a href="#GDB" accesskey="n" rel="next">Writing a new GDB backend</a>, Previous: <a href="#GCC" accesskey="p" rel="prev">Porting GCC</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Porting-newlib"></span><h2 class="chapter">3 Porting newlib</h2> <ul class="section-toc"> <li><a href="#Crt0" accesskey="1">Crt0, the main startup file</a></li> <li><a href="#Linker-Scripts" accesskey="2">Linker scripts for memory management</a></li> <li><a href="#What-to-do-now" accesskey="3">What to do when you have a binary image</a></li> <li><a href="#Libc" accesskey="4">Libraries</a></li> </ul> <hr> <div class="section" id="Crt0"> <div class="header"> <p> Next: <a href="#Linker-Scripts" accesskey="n" rel="next">Linker scripts for memory management</a>, Up: <a href="#Libraries" accesskey="u" rel="up">Porting newlib</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Crt0_002c-the-main-startup-file"></span><h3 class="section">3.1 Crt0, the main startup file</h3> <p>To make a program that has been compiled with GCC to run, you need to write some startup code. The initial piece of startup code is called a crt0. (C RunTime 0) This is usually written in assembler, and it’s object gets linked in first, and bootstraps the rest of the application when executed. This file needs to do the following things. </p> <ol> <li> Initialize anything that needs it. This init section varies. If you are developing an application that gets download to a ROM monitor, then there is usually no need for any special initialization. The ROM monitor handles it for you. <p>If you plan to burn your code in a ROM, then the crt0 typically has to do all the hardware initialization that is required to run an application. This can include things like initializing serial ports or run a memory check. It all depends on the hardware. </p> </li><li> Zero the BSS section. This is for uninitialized data. All the addresses in this section need to be initialized to zero so that programs that forget to check new variables default value will get unpredictable results. </li><li> Call main() This is what basically starts things running. If your ROM monitor supports it, then first setup argc and argv for command line arguments and an environment pointer. Then branch to main(). For G++ the the main routine gets a branch to __main inserted by the code generator at the very top. __main() is used by G++ to initialize it’s internal tables. __main() then returns back to your original main() and your code gets executed. </li><li> Call exit() After main() has returned, you need to cleanup things and return control of the hardware from the application. On some hardware, there is nothing to return to, especially if your program is in ROM. Sometimes the best thing to do in this case is do a hardware reset, or branch back to the start address all over again. <p>When there is a ROM monitor present, usually a user trap can be called and then the ROM takes over. Pick a safe vector with no side effects. Some ROMs have a builtin trap handler just for this case. </p></li></ol> <p>portable between all the m68k based boards we have here. <a href="#crt0_002eS">Example Crt0.S</a>. </p> <div class="example"> <pre class="example">/* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b </pre></div> <p>These we’ll use later. </p> <div class="example"> <pre class="example">/* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x) </pre></div> <p>These macros are to make this code portable between both <em>COFF</em> and <em>a.out</em>. <em>COFF</em> always has an <var>_ (underline)</var> prepended on the front of all global symbol names. <em>a.out</em> has none. </p> <div class="example"> <pre class="example">#ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp) </pre></div> <p>This is for portability between assemblers. Some register names have a <var>%</var> or <var>$</var> prepended to the register name. </p> <div class="example"> <pre class="example">/* * Set up some room for a stack. We just grab a chunk of memory. */ .set stack_size, 0x2000 .comm SYM (stack), stack_size </pre></div> <p>Set up space for the stack. This can also be done in the linker script, but it typically gets done here. </p> <div class="example"> <pre class="example">/* * Define an empty environment. */ .data .align 2 SYM (environ): .long 0 </pre></div> <p>Set up an empty space for the environment. This is bogus on any most ROM monitor, but we setup a valid address for it, and pass it to main. At least that way if an application checks for it, it won’t crash. </p> <div class="example"> <pre class="example"> .align2 .text .global SYM (stack) .global SYM (main) .global SYM (exit) /* * This really should be __bss_start, not SYM (__bss_start). */ .global __bss_start </pre></div> <p>Setup a few global symbols that get used elsewhere. <var>__bss_start</var> needs to be unchanged, as it’s setup by the linker script. </p> <div class="example"> <pre class="example">/* * start -- set things up so the application will run. */ SYM (start): link a6, #-8 moveal #SYM (stack) + stack_size, sp /* * zerobss -- zero out the bss section */ moveal #__bss_start, a0 moveal #SYM (end), a1 1: movel #0, (a0) leal4(a0), a0 cmpal a0, a1 bne1b </pre></div> <p>The global symbol <code>start</code> is used by the linker as the default address to use for the <code>.text</code> section. then it zeros the <code>.bss</code> section so the uninitialized data will all be cleared. Some programs have wild side effects from having the .bss section let uncleared. Particularly it causes problems with some implementations of <code>malloc</code>. </p> <div class="example"> <pre class="example">/* * Call the main routine from the application to get it going. * main (argc, argv, environ) * We pass argv as a pointer to NULL. */ pea 0 pea SYM (environ) pea sp@(4) pea 0 jsr SYM (main) movel d0, sp@- </pre></div> <p>Setup the environment pointer and jump to <code>main()</code>. When <code>main()</code> returns, it drops down to the <code>exit</code> routine below. </p> <div class="example"> <pre class="example">/* * _exit -- Exit from the application. Normally we cause a user trap * to return to the ROM monitor for another run. */ SYM (exit): trap #0 </pre></div> <p>Implementing <code>exit</code> here is easy. Both the <code>rom68k</code> and <code>bug</code> can handle a user caused exception of <code>zero</code> with no side effects. Although the <code>bug</code> monitor has a user caused trap that will return control to the ROM monitor, this solution has been more portable. </p> <hr> </div> <div class="section" id="Linker-Scripts"> <div class="header"> <p> Next: <a href="#What-to-do-now" accesskey="n" rel="next">What to do when you have a binary image</a>, Previous: <a href="#Crt0" accesskey="p" rel="prev">Crt0, the main startup file</a>, Up: <a href="#Libraries" accesskey="u" rel="up">Porting newlib</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Linker-scripts-for-memory-management"></span><h3 class="section">3.2 Linker scripts for memory management</h3> <p>The linker script sets up the memory map of an application. It also sets up default values for variables used elsewhere by sbrk() and the crt0. These default variables are typically called <code>_bss_start</code> and <code>_end</code>. </p> <p>For G++, the constructor and destructor tables must also be setup here. The actual section names vary depending on the object file format. For <code>a.out</code> and <code>coff</code>, the three main sections are <code>.text</code>, <code>.data</code>, and <code>.bss</code>. </p> <p>Now that you have an image, you can test to make sure it got the memory map right. You can do this by having the linker create a memory map (by using the <code>-Map</code> option), or afterwards by using <code>nm</code> to check a few critical addresses like <code>start</code>, <code>bss_end</code>, and <code>_etext</code>. </p> <p>Here’s a breakdown of a linker script for a m68k based target board. See the file <code>libgloss/m68k/idp.ld</code>, or go to the appendixes in the end of the manual. <a href="#idp_002eld">Example Linker Script</a>. </p> <div class="example"> <pre class="example">STARTUP(crt0.o) OUTPUT_ARCH(m68k) INPUT(idp.o) SEARCH_DIR(.) __DYNAMIC = 0; </pre></div> <p>The <code>STARTUP</code> command loads the file specified so that it’s first. In this case it also doubles to load the file as well, because the m68k-coff configuration defaults to not linking in the crt0.o by default. It assumes that the developer probably has their own crt0.o. This behavior is controlled in the config file for each architecture. It’s a macro called <code>STARTFILE_SPEC</code>, and if it’s set to <code>null</code>, then when <code>gcc</code> formats it’s command line, it doesn’t add <code>crto.o</code>. Any file name can be specified here, but the default is always <code>crt0.o</code>. </p> <p>Course if you only use <code>ld</code> to link, then the control of whether or not to link in <code>crt0.o</code> is done on the command line. If you have multiple crto files, then you can leave this out all together, and link in the <code>crt0.o</code> in the makefile, or by having different linker scripts. Sometimes this is done for initializing floating point optionally, or to add device support. </p> <p>The <code>OUTPUT_ARCH</code> sets architecture the output file is for. </p> <p><code>INPUT</code> loads in the file specified. In this case, it’s a relocated library that contains the definitions for the low-level functions need by libc.a. This could have also been specified on the command line, but as it’s always needed, it might as well be here as a default. <code>SEARCH_DIR</code> specifies the path to look for files, and <code>_DYNAMIC</code> means in this case there are no shared libraries. </p> <div class="example"> <pre class="example">/* * Setup the memory map of the MC68ec0x0 Board (IDP) * stack grows up towards high memory. This works for * both the rom68k and the mon68k monitors. */ MEMORY { ram : ORIGIN = 0x10000, LENGTH = 2M } </pre></div> <p>This specifies a name for a section that can be referred to later in the script. In this case, it’s only a pointer to the beginning of free RAM space, with an upper limit at 2M. If the output file exceeds the upper limit, it will produce an error message. </p> <div class="example"> <pre class="example">/* * stick everything in ram (of course) */ SECTIONS { .text : { CREATE_OBJECT_SYMBOLS *(.text) etext = .; __CTOR_LIST__ = .; LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) *(.ctors) LONG(0) __CTOR_END__ = .; __DTOR_LIST__ = .; LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) *(.dtors) LONG(0) __DTOR_END__ = .; *(.lit) *(.shdata) } > ram .shbss SIZEOF(.text) + ADDR(.text) : { *(.shbss) } </pre></div> <p>Set up the <code>.text</code> section. In a <code>COFF</code> file, .text is where all the actual instructions are. This also sets up the <em>CONTRUCTOR</em> and the <em>DESTRUCTOR</em> tables for <code>G++</code>. Notice that the section description redirects itself to the <em>ram</em> variable setup earlier. </p> <div class="example"> <pre class="example"> .talias : { } > ram .data : { *(.data) CONSTRUCTORS _edata = .; } > ram </pre></div> <p>Setup the <code>.data</code> section. In a <code>coff</code> file, this is where all he initialized data goes. <code>CONSTRUCTORS</code> is a special command used by <code>ld</code>. </p> <div class="example"> <pre class="example"> .bss SIZEOF(.data) + ADDR(.data) : { __bss_start = ALIGN(0x8); *(.bss) *(COMMON) end = ALIGN(0x8); _end = ALIGN(0x8); __end = ALIGN(0x8); } .mstack : { } > ram .rstack : { } > ram .stab . (NOLOAD) : { [ .stab ] } .stabstr . (NOLOAD) : { [ .stabstr ] } } </pre></div> <p>Setup the <code>.bss</code> section. In a <code>COFF</code> file, this is where unitialized data goes. The symbols <code>_bss_start</code> and <code>_end</code> are setup here for use by the <code>crt0.o</code> when it zero’s the <code>.bss</code> section. </p> <hr> </div> <div class="section" id="What-to-do-now"> <div class="header"> <p> Next: <a href="#Libc" accesskey="n" rel="next">Libraries</a>, Previous: <a href="#Linker-Scripts" accesskey="p" rel="prev">Linker scripts for memory management</a>, Up: <a href="#Libraries" accesskey="u" rel="up">Porting newlib</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="What-to-do-when-you-have-a-binary-image"></span><h3 class="section">3.3 What to do when you have a binary image</h3> <p>A few ROM monitors load binary images, typically <code>a.out</code>, but most all will load an <code>srecord</code>. An srecord is an ASCII representation of a binary image. At it’s simplest, an srecord is an address, followed by a byte count, followed by the bytes, and a 2’s compliment checksum. A whole srecord file has an optional <em>start</em> record, and a required <em>end</em> record. To make an srecord from a binary image, the GNU <code>objcopy</code> program is used. This will read the image and make an srecord from it. To do this, invoke objcopy like this: <code>objcopy -O srec infile outfile</code>. Most PROM burners also read srecords or a similar format. Use <code>objdump -i</code> to get a list of support object files types for your architecture. </p> <hr> </div> <div class="section" id="Libc"> <div class="header"> <p> Previous: <a href="#What-to-do-now" accesskey="p" rel="prev">What to do when you have a binary image</a>, Up: <a href="#Libraries" accesskey="u" rel="up">Porting newlib</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Libraries-1"></span><h3 class="section">3.4 Libraries</h3> <p>This describes <code>newlib</code>, a freely available libc replacement. Most applications use calls in the standard C library. When initially linking in libc.a, several I/O functions are undefined. If you don’t plan on doing any I/O, then you’re OK, otherwise they need to be created. These routines are read, write, open, close. sbrk, and kill. Open & close don’t need to be fully supported unless you have a filesystems, so typically they are stubbed out. Kill is also a stub, since you can’t do process control on an embedded system. </p> <p>Sbrk() is only needed by applications that do dynamic memory allocation. It’s uses the symbol <code>_end</code> that is setup in the linker script. It also requires a compile time option to set the upper size limit on the heap space. This leaves us with read and write, which are required for serial I/O. Usually these two routines are written in C, and call a lower level function for the actual I/O operation. These two lowest level I/O primitives are inbyte() and outbyte(), and are also used by GDB back ends if you’ve written an exception handler. Some systems also implement a havebyte() for input as well. </p> <p>Other commonly included functions are routines for manipulating LED’s on the target (if they exist) or low level debug help. Typically a putnum() for printing words and bytes as a hex number is helpful, as well as a low-level print() to output simple strings. </p> <p>As libg++ uses the I/O routines in libc.a, if read and write work, then libg++ will also work with no additional changes. </p> <ul class="section-toc"> <li><a href="#I_002fO-Support" accesskey="1">Making I/O work</a></li> <li><a href="#Memory-Support" accesskey="2">Routines for dynamic memory allocation</a></li> <li><a href="#Misc-Support" accesskey="3">Misc support routines</a></li> <li><a href="#Debugging" accesskey="4">Useful debugging functions</a></li> </ul> <hr> <div class="subsection" id="I_002fO-Support"> <div class="header"> <p> Next: <a href="#Memory-Support" accesskey="n" rel="next">Routines for dynamic memory allocation</a>, Up: <a href="#Libc" accesskey="u" rel="up">Libraries</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Making-I_002fO-work"></span><h4 class="subsection">3.4.1 Making I/O work</h4> <hr> </div> <div class="subsection" id="Memory-Support"> <div class="header"> <p> Next: <a href="#Misc-Support" accesskey="n" rel="next">Misc support routines</a>, Previous: <a href="#I_002fO-Support" accesskey="p" rel="prev">Making I/O work</a>, Up: <a href="#Libc" accesskey="u" rel="up">Libraries</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Routines-for-dynamic-memory-allocation"></span><h4 class="subsection">3.4.2 Routines for dynamic memory allocation</h4> <p>To support using any of the memory functions, you need to implement sbrk(). <code>malloc()</code>, <code>calloc()</code>, and <code>realloc()</code> all call <code>sbrk()</code> at there lowest level. <code>caddr_t</code> is defined elsewhere as <code>char *</code>. <code>RAMSIZE</code> is presently a compile time option. All this does is move a pointer to heap memory and check for the upper limit. <a href="#glue_002ec">Example libc support code</a>. <code>sbrk()</code> returns a pointer to the previous value before more memory was allocated. </p> <div class="example"> <pre class="example">/* _end is set in the linker command file * extern caddr_t _end;/ /* just in case, most boards have at least some memory */ #ifndef RAMSIZE # define RAMSIZE (caddr_t)0x100000 #endif /* * sbrk -- changes heap size size. Get nbytes more * RAM. We just increment a pointer in what's * left of memory on the board. */ caddr_t sbrk(nbytes) int nbytes; { static caddr_t heap_ptr = NULL; caddr_t base; if (heap_ptr == NULL) { heap_ptr = (caddr_t)&_end; } if ((RAMSIZE - heap_ptr) >= 0) { base = heap_ptr; heap_ptr += nbytes; return (base); } else { errno = ENOMEM; return ((caddr_t)-1); } } </pre></div> <hr> </div> <div class="subsection" id="Misc-Support"> <div class="header"> <p> Next: <a href="#Debugging" accesskey="n" rel="next">Useful debugging functions</a>, Previous: <a href="#Memory-Support" accesskey="p" rel="prev">Routines for dynamic memory allocation</a>, Up: <a href="#Libc" accesskey="u" rel="up">Libraries</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Misc-support-routines"></span><h4 class="subsection">3.4.3 Misc support routines</h4> <p>These are called by <code>newlib</code> but don’t apply to the embedded environment. <code>isatty()</code> is self explanatory. <code>kill()</code> doesn’t apply either in an environment withno process control, so it justs exits, which is a similar enough behavior. <code>getpid()</code> can safely return any value greater than 1. The value doesn’t effect anything in <code>newlib</code> because once again there is no process control. </p> <div class="example"> <pre class="example">/* * isatty -- returns 1 if connected to a terminal device, * returns 0 if not. Since we're hooked up to a * serial port, we'll say yes and return a 1. */ int isatty(fd) int fd; { return (1); } /* * getpid -- only one process, so just return 1. */ #define __MYPID 1 int getpid() { return __MYPID; } /* * kill -- go out via exit... */ int kill(pid, sig) int pid; int sig; { if(pid == __MYPID) _exit(sig); return 0; } </pre></div> <hr> </div> <div class="subsection" id="Debugging"> <div class="header"> <p> Previous: <a href="#Misc-Support" accesskey="p" rel="prev">Misc support routines</a>, Up: <a href="#Libc" accesskey="u" rel="up">Libraries</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Useful-debugging-functions"></span><h4 class="subsection">3.4.4 Useful debugging functions</h4> <p>There are always a few useful functions for debugging your project in progress. I typically implement a simple <code>print()</code> routine that runs standalone in liblgoss, with no <code>newlib</code> support. The I/O function <code>outbyte()</code> can also be used for low level debugging. Many times print will work when there are problems that cause <code>printf()</code> to cause an exception. <code>putnum()</code> is just to print out values in hex so they are easier to read. </p> <div class="example"> <pre class="example">/* * print -- do a raw print of a string */ int print(ptr) char *ptr; { while (*ptr) { outbyte (*ptr++); } } /* * putnum -- print a 32 bit number in hex */ int putnum (num) unsigned int num; { char buffer[9]; int count; char *bufptr = buffer; int digit; for (count = 7 ; count >= 0 ; count--) { digit = (num >> (count * 4)) & 0xf; if (digit <= 9) *bufptr++ = (char) ('0' + digit); else *bufptr++ = (char) ('a' - 10 + digit); } *bufptr = (char) 0; print (buffer); return; } </pre></div> <p>If there are LEDs on the board, they can also be put to use for debugging when the serial I/O code is being written. I usually implement a <code>zylons()</code> function, which strobes the LEDS (if there is more than one) in sequence, creating a rotating effect. This is convenient between I/O to see if the target is still alive. Another useful LED function is <code>led_putnum()</code>, which takes a digit and displays it as a bit pattern or number. These usually have to be written in assembler for each target board. Here are a number of C based routines that may be useful. </p> <p><code>led_putnum()</code> puts a number on a single digit segmented LED display. This LED is set by setting a bit mask to an address, where 1 turns the segment off, and 0 turns it on. There is also a little decimal point on the LED display, so it gets the leftmost bit. The other bits specify the segment location. The bits look like: </p> <div class="example"> <pre class="example"> [d.p | g | f | e | d | c | b | a ] is the byte. </pre></div> <p>The locations are set up as: </p> <div class="example"> <pre class="example"> a ----- f | | b | g | ----- | | e | | c ----- d </pre></div> <p>This takes a number that’s already been converted to a string, and prints it. </p> <div class="example"> <pre class="example">#define LED_ADDR0xd00003 void led_putnum ( num ) char num; { static unsigned char *leds = (unsigned char *)LED_ADDR; static unsigned char num_bits [18] = { 0xff, /* clear all */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x98, /* numbers 0-9 */ 0x98, 0x20, 0x3, 0x27, 0x21, 0x4, 0xe /* letters a-f */ }; if (num >= '0' && num <= '9') num = (num - '0') + 1; if (num >= 'a' && num <= 'f') num = (num - 'a') + 12; if (num == ' ') num = 0; *leds = num_bits[num]; } /* * zylons -- draw a rotating pattern. NOTE: this function never returns. */ void zylons() { unsigned char *leds = (unsigned char *)LED_ADDR; unsigned char curled = 0xfe; while (1) { *leds = curled; curled = (curled >> 1) | (curled << 7); delay ( 200 ); } } </pre></div> <hr> </div> </div> </div> <div class="chapter" id="GDB"> <div class="header"> <p> Next: <a href="#Binutils" accesskey="n" rel="next">Binutils</a>, Previous: <a href="#Libraries" accesskey="p" rel="prev">Porting newlib</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Writing-a-new-GDB-backend"></span><h2 class="chapter">4 Writing a new GDB backend</h2> <p>Typically, either the low-level I/O routines are used for debugging, or LEDs, if present. It is much easier to use GDb for debugging an application. There are several different techniques used to have GDB work remotely. Commonly more than one kind of GDB interface is used to cober a wide variety of development needs. </p> <p>The most common style of GDB backend is an exception handler for breakpoints. This is also called a <em>gdb stub</em>, and is requires the two additional lines of init code in your <code>main()</code> routine. The GDB stubs all use the GDB <em>remote protocol</em>. When the application gets a breakpoint exception, it communicates to GDB on the host. </p> <p>Another common style of interfacing GDB to a target is by using an existing ROM monitor. These break down into two main kinds, a similar protocol to the GDB remote protocol, and an interface that uses the ROM monitor directly. This kind has GDB simulating a human operator, and all GDB does is work as a command formatter and parser. </p> <ul class="section-toc"> <li><a href="#GNU-remote-protocol" accesskey="1">The standard remote protocol</a></li> <li><a href="#Exception-handler" accesskey="2">A linked in exception handler</a></li> <li><a href="#ROM-monitors" accesskey="3">Using a ROM monitor as a backend</a></li> <li><a href="#Other-remote-protocols" accesskey="4">Adding support for new protocols</a></li> </ul> <hr> <div class="section" id="GNU-remote-protocol"> <div class="header"> <p> Next: <a href="#Exception-handler" accesskey="n" rel="next">A linked in exception handler</a>, Up: <a href="#GDB" accesskey="u" rel="up">Writing a new GDB backend</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="The-standard-remote-protocol"></span><h3 class="section">4.1 The standard remote protocol</h3> <p>The standard remote protocol is a simple, packet based scheme. A debug packet whose contents are <em><data></em> is encapsulated for transmission in the form: </p> <div class="example"> <pre class="example">$ <data> # CSUM1 CSUM2 </pre></div> <p><em><data></em> must be ASCII alphanumeric and cannot include characters <code>$</code> or <code>#</code>. If <em><data></em> starts with two characters followed by <code>:</code>, then the existing stubs interpret this as a sequence number. For example, the command <code>g</code> is used to read the values of the registers. So, a packet to do this would look like </p> <div class="example"> <pre class="example"> $g#67 </pre></div> <p><em>CSUM1</em> and <em>CSUM2</em> are an ascii representation in hex of an 8-bit checksum of <em><data></em>, the most significant nibble is sent first. the hex digits 0-9,a-f are used. </p> <p>A simple protocol is used when communicating with the target. This is mainly to give a degree of error handling over the serial cable. For each packet transmitted successfully, the target responds with a <code>+</code> (<code>ACK</code>). If there was a transmission error, then the target responds with a <code>-</code> (<code>NAK</code>). An error is determined when the checksum doesn’t match the calculated checksum for that data record. Upon reciept of the <code>ACK</code>, <code>GDB</code> can then transmit the next packet. </p> <p>Here is a list of the main functions that need to be supported. Each data packet is a command with a set number of bytes in the command packet. Most commands either return data, or respond with a <code>NAK</code>. Commands that don’t return data respond with an <code>ACK</code>. All data values are ascii hex digits. Every byte needs two hex digits to represent t. This means that a byte with the value ‘<samp>7</samp>’ becomes ‘<samp>07</samp>’. On a 32 bit machine this works out to 8 characters per word. All of the bytes in a word are stored in the target byte order. When writing the host side of the GDB protocol, be careful of byte order, and make sure that the code will run on both big and little endian hosts and produce the same answers. </p> <p>These functions are the minimum required to make a GDB backend work. All other commands are optional, and not supported by all GDB backends. </p> <dl compact="compact"> <dt><span>‘<samp>read registers <code>g</code></samp>’</span></dt> <dd> <p>returns <code>XXXXXXXX...</code> </p> <p>Registers are in the internal order for GDB, and the bytes in a register are in the same order the machine uses. All values are in sequence starting with register 0. All registers are listed in the same packet. A sample packet would look like <code>$g#</code>. </p> </dd> <dt><span>‘<samp>write registers<code>GXXXXXXXX...</code></samp>’</span></dt> <dd><p><code>XXXXXXXX</code> is the value to set the register to. Registers are in the internal order for GDB, and the bytes in a register are in the same order the machine uses. All values are in sequence starting with register 0. All registers values are listed in the same packet. A sample packet would look like <code>$G000000001111111122222222...#</code> </p> <p>returns <code>ACK</code> or <code>NAK</code> </p> </dd> <dt><span>‘<samp>read memory <code>mAAAAAAAA,LLLL</code></samp>’</span></dt> <dd><p><code>AAAAAAAA</code> is address, <code>LLLL</code> is length. A sample packet would look like <code>$m00005556,0024#</code>. This would request 24 bytes starting at address <em>00005556</em> </p> <p>returns <code>XXXXXXXX...</code> <code>XXXXXXXX</code> is the memory contents. Fewer bytes than requested will be returned if only part of the data can be read. This can be determined by counting the values till the end of packet <code>#</code> is seen and comparing that with the total count of bytes that was requested. </p> </dd> <dt><span>‘<samp>write memory<code>MAAAAAAAA,LLLL:XXXXXXXX</code></samp>’</span></dt> <dd><p><code>AAAAAAAA</code> is the starting address, <code>LLLL</code> is the number of bytes to be written, and <code>XXXXXXXX</code> is value to be written. A sample packet would look like <code>$M00005556,0024:101010101111111100000000...#</code> </p> <p>returns <code>ACK</code> or <code>NAK</code> for an error. <code>NAK</code> is also returned when only part of the data is written. </p> </dd> <dt><span>‘<samp>continue<code>cAAAAAAAAA</code></samp>’</span></dt> <dd><p><code>AAAAAAAA</code> is address to resume execution at. If <code>AAAAAAAA</code> is omitted, resume at the curent address of the <code>pc</code> register. </p> <p>returns the same replay as <code>last signal</code>. There is no immediate replay to <code>cont</code> until the next breakpoint is reached, and the program stops executing. </p> </dd> <dt><span>‘<samp>step sAA..AA</samp>’</span></dt> <dd><p><code>AA..AA</code> is address to resume If <code>AA..AA</code> is omitted, resume at same address. </p> <p>returns the same replay as <code>last signal</code>. There is no immediate replay to <code>step</code> until the next breakpoint is reached, and the program stops executing. </p> </dd> <dt><span>‘<samp>last signal <code>?</code></samp>’</span></dt> <dd> <p>This returns one of the following: </p> <ul> <li> <code>SAA</code> Where <code>AA</code> is the number of the last signal. Exceptions on the target are converted to the most similar Unix style signal number, like <code>SIGSEGV</code>. A sample response of this type would look like <code>$S05#</code>. </li><li> TAAnn:XXXXXXXX;nn:XXXXXXXX;nn:XXXXXXXX; <code>AA</code> is the signal number. <code>nn</code> is the register number. <code>XXXXXXXX</code> is the register value. </li><li> WAA The process exited, and <code>AA</code> is the exit status. This is only applicable for certains sorts of targets. </li></ul> <p>These are used in some GDB backends, but not all. </p> </dd> <dt><span>‘<samp>write reg <code>Pnn=XXXXXXXX</code></samp>’</span></dt> <dd><p>Write register <code>nn</code> with value <code>XXXXXXXX</code>. </p> <p>returns <code>ACK</code> or <code>NAK</code> </p> </dd> <dt><span>‘<samp>kill request k</samp>’</span></dt> <dt><span>‘<samp>toggle debug d</samp>’</span></dt> <dd><p>toggle debug flag (see 386 & 68k stubs) </p> </dd> <dt><span>‘<samp>reset r</samp>’</span></dt> <dd><p>reset – see sparc stub. </p> </dd> <dt><span>‘<samp>reserved<code>other</code></samp>’</span></dt> <dd><p>On other requests, the stub should ignore the request and send an empty response <code>$#<checksum></code>. This way we can extend the protocol and GDB can tell whether the stub it is talking to uses the old or the new. </p> </dd> <dt><span>‘<samp>search<code>tAA:PP,MM</code></samp>’</span></dt> <dd><p>Search backwards starting at address <code>AA</code> for a match with pattern PP and mask <code>MM</code>. <code>PP</code> and <code>MM</code> are 4 bytes. </p> </dd> <dt><span>‘<samp>general query<code>qXXXX</code></samp>’</span></dt> <dd><p>Request info about XXXX. </p> </dd> <dt><span>‘<samp>general set<code>QXXXX=yyyy</code></samp>’</span></dt> <dd><p>Set value of <code>XXXX</code> to <code>yyyy</code>. </p> </dd> <dt><span>‘<samp>query sect offs<code>qOffsets</code></samp>’</span></dt> <dd><p>Get section offsets. Reply is <code>Text=xxx;Data=yyy;Bss=zzz</code> </p> </dd> <dt><span>‘<samp>console output Otext</samp>’</span></dt> <dd><p>Send text to stdout. The text gets display from the target side of the serial connection. </p> </dd> </dl> <p>Responses can be run-length encoded to save space. A <code>*</code>means that the next character is an ASCII encoding giving a repeat count which stands for that many repetitions of the character preceding the <code>*</code>. The encoding is n+29, yielding a printable character where n >=3 (which is where run length encoding starts to win). You can’t use a value of where n >126 because it’s only a two byte value. An example would be a <code>0*03</code> means the same thing as <code>0000</code>. </p> <hr> </div> <div class="section" id="Exception-handler"> <div class="header"> <p> Next: <a href="#ROM-monitors" accesskey="n" rel="next">Using a ROM monitor as a backend</a>, Previous: <a href="#GNU-remote-protocol" accesskey="p" rel="prev">The standard remote protocol</a>, Up: <a href="#GDB" accesskey="u" rel="up">Writing a new GDB backend</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="A-linked-in-exception-handler"></span><h3 class="section">4.2 A linked in exception handler</h3> <p>A <em>GDB stub</em> consists of two parts, support for the exception handler, and the exception handler itself. The exception handler needs to communicate to GDB on the host whenever there is a breakpoint exception. When GDB starts a program running on the target, it’s polling the serial port during execution looking for any debug packets. So when a breakpoint occurs, the exception handler needs to save state, and send a GDB remote protocol packet to GDB on the host. GDB takes any output that isn’t a debug command packet and displays it in the command window. </p> <p>Support for the exception handler varies between processors, but the minimum supported functions are those needed by GDB. These are functions to support the reading and writing of registers, the reading and writing of memory, start execution at an address, single step, and last signal. Sometimes other functions for adjusting the baud rate, or resetting the hardware are implemented. </p> <p>Once GDB gets the command packet from the breakpoint, it will read a few registers and memory locations an then wait for the user. When the user types <code>run</code> or <code>continue</code> a <code>continue</code> command is issued to the backend, and control returns from the breakpoint routine to the application. </p> <hr> </div> <div class="section" id="ROM-monitors"> <div class="header"> <p> Next: <a href="#Other-remote-protocols" accesskey="n" rel="next">Adding support for new protocols</a>, Previous: <a href="#Exception-handler" accesskey="p" rel="prev">A linked in exception handler</a>, Up: <a href="#GDB" accesskey="u" rel="up">Writing a new GDB backend</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Using-a-ROM-monitor-as-a-backend"></span><h3 class="section">4.3 Using a ROM monitor as a backend</h3> <p>GDB also can mimic a human user and use a ROM monitors normal debug commands as a backend. This consists mostly of sending and parsing <code>ASCII</code> strings. All the ROM monitor interfaces share a common set of routines in <code>gdb/monitor.c</code>. This supports adding new ROM monitor interfaces by filling in a structure with the common commands GDB needs. GDb already supports several command ROM monitors, including Motorola’s <code>Bug</code> monitor for their VME boards, and the Rom68k monitor by Integrated Systems, Inc. for various m68k based boards. GDB also supports the custom ROM monitors on the WinBond and Oki PA based targets. There is builtin support for loading files to ROM monitors specifically. GDB can convert a binary into an srecord and then load it as an ascii file, or using <code>xmodem</code>. </p> <hr> </div> <div class="section" id="Other-remote-protocols"> <div class="header"> <p> Previous: <a href="#ROM-monitors" accesskey="p" rel="prev">Using a ROM monitor as a backend</a>, Up: <a href="#GDB" accesskey="u" rel="up">Writing a new GDB backend</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Adding-support-for-new-protocols"></span><h3 class="section">4.4 Adding support for new protocols</h3> <hr> <span id="Binutils"></span><div class="header"> <p> Next: <a href="#Code-Listings" accesskey="n" rel="next">Code Listings</a>, Previous: <a href="#GDB" accesskey="p" rel="prev">Writing a new GDB backend</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <h4 class="node-heading">Binutils</h4> <hr> </div> </div> <div class="appendix" id="Code-Listings"> <div class="header"> <p> Next: <a href="#idp_002eld" accesskey="n" rel="next">Linker script for the IDP board</a>, Previous: <a href="#Binutils" accesskey="p" rel="prev">Binutils</a>, Up: <a href="#Top" accesskey="u" rel="up">Embed with GNU</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Code-Listings-1"></span><h2 class="appendix">Appendix A Code Listings</h2> <ul class="section-toc"> <li><a href="#idp_002eld" accesskey="1">Linker script for the IDP board</a></li> <li><a href="#crt0_002eS" accesskey="2">crt0.S - The startup file</a></li> <li><a href="#glue_002ec" accesskey="3">C based "glue" code.</a></li> <li><a href="#mvme_002eS" accesskey="4">I/O assembler code sample</a></li> <li><a href="#io_002ec" accesskey="5">I/O code sample</a></li> <li><a href="#leds_002ec" accesskey="6">Led control sample</a></li> </ul> <hr> <div class="section" id="idp_002eld"> <div class="header"> <p> Next: <a href="#crt0_002eS" accesskey="n" rel="next">crt0.S - The startup file</a>, Previous: <a href="#Code-Listings" accesskey="p" rel="prev">Code Listings</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Linker-script-for-the-IDP-board"></span><h3 class="section">A.1 Linker script for the IDP board</h3> <p>This is the linker script script that is used on the Motorola IDP board. </p> <div class="example"> <pre class="example">STARTUP(crt0.o) OUTPUT_ARCH(m68k) INPUT(idp.o) SEARCH_DIR(.) __DYNAMIC = 0; /* * Setup the memory map of the MC68ec0x0 Board (IDP) * stack grows up towards high memory. This works for * both the rom68k and the mon68k monitors. */ MEMORY { ram : ORIGIN = 0x10000, LENGTH = 2M } /* * stick everything in ram (of course) */ SECTIONS { .text : { CREATE_OBJECT_SYMBOLS *(.text) etext = .; __CTOR_LIST__ = .; LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) *(.ctors) LONG(0) __CTOR_END__ = .; __DTOR_LIST__ = .; LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) *(.dtors) LONG(0) __DTOR_END__ = .; *(.lit) *(.shdata) } > ram .shbss SIZEOF(.text) + ADDR(.text) : { *(.shbss) } .talias : { } > ram .data : { *(.data) CONSTRUCTORS _edata = .; } > ram .bss SIZEOF(.data) + ADDR(.data) : { __bss_start = ALIGN(0x8); *(.bss) *(COMMON) end = ALIGN(0x8); _end = ALIGN(0x8); __end = ALIGN(0x8); } .mstack : { } > ram .rstack : { } > ram .stab . (NOLOAD) : { [ .stab ] } .stabstr . (NOLOAD) : { [ .stabstr ] } } </pre></div> <hr> </div> <div class="section" id="crt0_002eS"> <div class="header"> <p> Next: <a href="#glue_002ec" accesskey="n" rel="next">C based "glue" code.</a>, Previous: <a href="#idp_002eld" accesskey="p" rel="prev">Linker script for the IDP board</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="crt0_002eS-_002d-The-startup-file"></span><h3 class="section">A.2 crt0.S - The startup file</h3> <div class="example"> <pre class="example">/* * crt0.S -- startup file for m68k-coff * */ .title "crt0.S for m68k-coff" /* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif #ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x) /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp) /* * Set up some room for a stack. We just grab a chunk of memory. */ .set stack_size, 0x2000 .comm SYM (stack), stack_size /* * Define an empty environment. */ .data .align 2 SYM (environ): .long 0 .align2 .text .global SYM (stack) .global SYM (main) .global SYM (exit) /* * This really should be __bss_start, not SYM (__bss_start). */ .global __bss_start /* * start -- set things up so the application will run. */ SYM (start): link a6, #-8 moveal #SYM (stack) + stack_size, sp /* * zerobss -- zero out the bss section */ moveal #__bss_start, a0 moveal #SYM (end), a1 1: movel #0, (a0) leal4(a0), a0 cmpal a0, a1 bne1b /* * Call the main routine from the application to get it going. * main (argc, argv, environ) * We pass argv as a pointer to NULL. */ pea 0 pea SYM (environ) pea sp@(4) pea 0 jsr SYM (main) movel d0, sp@- /* * _exit -- Exit from the application. Normally we cause a user trap * to return to the ROM monitor for another run. */ SYM (exit): trap #0 </pre></div> <hr> </div> <div class="section" id="glue_002ec"> <div class="header"> <p> Next: <a href="#mvme_002eS" accesskey="n" rel="next">I/O assembler code sample</a>, Previous: <a href="#crt0_002eS" accesskey="p" rel="prev">crt0.S - The startup file</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="C-based-_0022glue_0022-code_002e"></span><h3 class="section">A.3 C based "glue" code.</h3> <div class="example"> <pre class="example"> /* * glue.c -- all the code to make GCC and the libraries run on * a bare target board. These should work with any * target if inbyte() and outbyte() exist. */ #include <sys/types.h> #include <sys/stat.h> #include <errno.h> #ifndef NULL #define NULL 0 #endif /* FIXME: this is a hack till libc builds */ __main() { return; } #undef errno int errno; extern caddr_t _end; /* _end is set in the linker command file */ extern int outbyte(); extern unsigned char inbyte(); extern int havebyte(); /* just in case, most boards have at least some memory */ #ifndef RAMSIZE # define RAMSIZE (caddr_t)0x100000 #endif /* * read -- read bytes from the serial port. Ignore fd, since * we only have stdin. */ int read(fd, buf, nbytes) int fd; char *buf; int nbytes; { int i = 0; for (i = 0; i < nbytes; i++) { *(buf + i) = inbyte(); if ((*(buf + i) == '\n') || (*(buf + i) == '\r')) { (*(buf + i)) = 0; break; } } return (i); } /* * write -- write bytes to the serial port. Ignore fd, since * stdout and stderr are the same. Since we have no filesystem, * open will only return an error. */ int write(fd, buf, nbytes) int fd; char *buf; int nbytes; { int i; for (i = 0; i < nbytes; i++) { if (*(buf + i) == '\n') { outbyte ('\r'); } outbyte (*(buf + i)); } return (nbytes); } /* * open -- open a file descriptor. We don't have a filesystem, so * we return an error. */ int open(buf, flags, mode) char *buf; int flags; int mode; { errno = EIO; return (-1); } /* * close -- close a file descriptor. We don't need * to do anything, but pretend we did. */ int close(fd) int fd; { return (0); } /* * sbrk -- changes heap size size. Get nbytes more * RAM. We just increment a pointer in what's * left of memory on the board. */ caddr_t sbrk(nbytes) int nbytes; { static caddr_t heap_ptr = NULL; caddr_t base; if (heap_ptr == NULL) { heap_ptr = (caddr_t)&_end; } if ((RAMSIZE - heap_ptr) >= 0) { base = heap_ptr; heap_ptr += nbytes; return (base); } else { errno = ENOMEM; return ((caddr_t)-1); } } /* * isatty -- returns 1 if connected to a terminal device, * returns 0 if not. Since we're hooked up to a * serial port, we'll say yes and return a 1. */ int isatty(fd) int fd; { return (1); } /* * lseek -- move read/write pointer. Since a serial port * is non-seekable, we return an error. */ off_t lseek(fd, offset, whence) int fd; off_t offset; int whence; { errno = ESPIPE; return ((off_t)-1); } /* * fstat -- get status of a file. Since we have no file * system, we just return an error. */ int fstat(fd, buf) int fd; struct stat *buf; { errno = EIO; return (-1); } /* * getpid -- only one process, so just return 1. */ #define __MYPID 1 int getpid() { return __MYPID; } /* * kill -- go out via exit... */ int kill(pid, sig) int pid; int sig; { if(pid == __MYPID) _exit(sig); return 0; } /* * print -- do a raw print of a string */ int print(ptr) char *ptr; { while (*ptr) { outbyte (*ptr++); } } /* * putnum -- print a 32 bit number in hex */ int putnum (num) unsigned int num; { char buffer[9]; int count; char *bufptr = buffer; int digit; for (count = 7 ; count >= 0 ; count--) { digit = (num >> (count * 4)) & 0xf; if (digit <= 9) *bufptr++ = (char) ('0' + digit); else *bufptr++ = (char) ('a' - 10 + digit); } *bufptr = (char) 0; print (buffer); return; } </pre></div> <hr> </div> <div class="section" id="mvme_002eS"> <div class="header"> <p> Next: <a href="#io_002ec" accesskey="n" rel="next">I/O code sample</a>, Previous: <a href="#glue_002ec" accesskey="p" rel="prev">C based "glue" code.</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="I_002fO-assembler-code-sample"></span><h3 class="section">A.4 I/O assembler code sample</h3> <div class="example"> <pre class="example">/* * mvme.S -- board support for m68k */ .title "mvme.S for m68k-coff" /* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif #ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x) /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp) #define vbr REG (vbr) .align2 .text .global SYM (_exit) .global SYM (outln) .global SYM (outbyte) .global SYM (putDebugChar) .global SYM (inbyte) .global SYM (getDebugChar) .global SYM (havebyte) .global SYM (exceptionHandler) .set vbr_size, 0x400 .comm SYM (vbr_table), vbr_size /* * inbyte -- get a byte from the serial port * d0 - contains the byte read in */ .align2 SYM (getDebugChar): /* symbol name used by m68k-stub */ SYM (inbyte): link a6, #-8 trap #15 .word inchr moveb sp@, d0 extbl d0 unlk a6 rts /* * outbyte -- sends a byte out the serial port * d0 - contains the byte to be sent */ .align2 SYM (putDebugChar): /* symbol name used by m68k-stub */ SYM (outbyte): link fp, #-4 moveb fp@(11), sp@ trap #15 .word outchr unlk fp rts /* * outln -- sends a string of bytes out the serial port with a CR/LF * a0 - contains the address of the string's first byte * a1 - contains the address of the string's last byte */ .align2 SYM (outln): link a6, #-8 moveml a0/a1, sp@ trap #15 .word outln unlk a6 rts /* * outstr -- sends a string of bytes out the serial port without a CR/LF * a0 - contains the address of the string's first byte * a1 - contains the address of the string's last byte */ .align2 SYM (outstr): link a6, #-8 moveml a0/a1, sp@ trap #15 .word outstr unlk a6 rts /* * havebyte -- checks to see if there is a byte in the serial port, * returns 1 if there is a byte, 0 otherwise. */ SYM (havebyte): trap #15 .word instat beqs empty movel #1, d0 rts empty: movel #0, d0 rts /* * These constants are for the MVME-135 board's boot monitor. They * are used with a TRAP #15 call to access the monitor's I/O routines. * they must be in the word following the trap call. */ .set inchr, 0x0 .set instat, 0x1 .set inln, 0x2 .set readstr, 0x3 .set readln, 0x4 .set chkbrk, 0x5 .set outchr, 0x20 .set outstr, 0x21 .set outln, 0x22 .set write, 0x23 .set writeln, 0x24 .set writdln, 0x25 .set pcrlf, 0x26 .set eraseln, 0x27 .set writd, 0x28 .set sndbrk, 0x29 .set tm_ini, 0x40 .set dt_ini, 0x42 .set tm_disp, 0x43 .set tm_rd, 0x44 .set redir, 0x60 .set redir_i, 0x61 .set redir_o, 0x62 .set return, 0x63 .set bindec, 0x64 .set changev, 0x67 .set strcmp, 0x68 .set mulu32, 0x69 .set divu32, 0x6A .set chk_sum, 0x6B </pre></div> <hr> </div> <div class="section" id="io_002ec"> <div class="header"> <p> Next: <a href="#leds_002ec" accesskey="n" rel="next">Led control sample</a>, Previous: <a href="#mvme_002eS" accesskey="p" rel="prev">I/O assembler code sample</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="I_002fO-code-sample"></span><h3 class="section">A.5 I/O code sample</h3> <div class="example"> <pre class="example">#include "w89k.h" /* * outbyte -- shove a byte out the serial port. We wait till the byte */ int outbyte(byte) unsigned char byte; { while ((inp(RS232REG) & TRANSMIT) == 0x0) { } ; return (outp(RS232PORT, byte)); } /* * inbyte -- get a byte from the serial port */ unsigned char inbyte() { while ((inp(RS232REG) & RECEIVE) == 0x0) { }; return (inp(RS232PORT)); } </pre></div> <hr> </div> <div class="section" id="leds_002ec"> <div class="header"> <p> Previous: <a href="#io_002ec" accesskey="p" rel="prev">I/O code sample</a>, Up: <a href="#Code-Listings" accesskey="u" rel="up">Code Listings</a> [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> </div> <span id="Led-control-sample"></span><h3 class="section">A.6 Led control sample</h3> <div class="example"> <pre class="example">/* * leds.h -- control the led's on a Motorola mc68ec0x0 board. */ #ifndef __LEDS_H__ #define __LEDS_H__ #define LED_ADDR0xd00003 #define LED_0 ~0x1 #define LED_1 ~0x2 #define LED_2 ~0x4 #define LED_3 ~0x8 #define LED_4 ~0x10 #define LED_5 ~0x20 #define LED_6 ~0x40 #define LED_7 ~0x80 #define LEDS_OFF0xff #define LEDS_ON0x0 #define FUDGE(x) ((x >= 0xa && x <= 0xf) ? (x + 'a') & 0x7f : (x + '0') & 0x7f) extern void led_putnum( char ); #endif /* __LEDS_H__ */ /* * leds.c -- control the led's on a Motorola mc68ec0x0 (IDP)board. */ #include "leds.h" void zylons(); void led_putnum(); /* * led_putnum -- print a hex number on the LED. the value of num must be a char with * the ascii value. ie... number 0 is '0', a is 'a', ' ' (null) clears * the led display. * Setting the bit to 0 turns it on, 1 turns it off. * the LED's are controlled by setting the right bit mask in the base * address. * The bits are: * [d.p | g | f | e | d | c | b | a ] is the byte. * * The locations are: * * a * ----- * f | | b * | g | * ----- * | | * e | | c * ----- * d . d.p (decimal point) */ void led_putnum ( num ) char num; { static unsigned char *leds = (unsigned char *)LED_ADDR; static unsigned char num_bits [18] = { 0xff, /* clear all */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x98, /* numbers 0-9 */ 0x98, 0x20, 0x3, 0x27, 0x21, 0x4, 0xe /* letters a-f */ }; if (num >= '0' && num <= '9') num = (num - '0') + 1; if (num >= 'a' && num <= 'f') num = (num - 'a') + 12; if (num == ' ') num = 0; *leds = num_bits[num]; } /* * zylons -- draw a rotating pattern. NOTE: this function never returns. */ void zylons() { unsigned char *leds = (unsigned char *)LED_ADDR; unsigned char curled = 0xfe; while (1) { *leds = curled; curled = (curled >> 1) | (curled << 7); delay ( 200 ); } } </pre></div> </div> </div> </div> </body> </html>
|
