stm32/mboot: Add MBOOT_LEAVE_BOOTLOADER_VIA_RESET option.

It is enabled by default to get the standard behaviour of doing a reset after it is finished, but can be disabled by a board to jump straight to the application (likely the board needs to use MBOOT_BOARD_CLEANUP to make this work). The application is passed a reset mode of BOARDCTRL_RESET_MODE_BOOTLOADER if the bootloader was active and entered via a jump. Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

ports/stm32/mboot/main.c

@@ -40,6 +40,11 @@
 #include "dfu.h"
 #include "pack.h"
 
+// Whether the bootloader will leave via reset, or direct jump to the application.
+#ifndef MBOOT_LEAVE_BOOTLOADER_VIA_RESET
+#define MBOOT_LEAVE_BOOTLOADER_VIA_RESET (1)
+#endif
+
 // This option selects whether to use explicit polling or IRQs for USB events.
 // In some test cases polling mode can run slightly faster, but it uses more power.
 // Polling mode will also cause failures with the mass-erase command because USB
@@ -1329,6 +1334,45 @@ static int get_reset_mode(void) {
  return reset_mode;
 }
 
+NORETURN static __attribute__((naked)) void branch_to_application(uint32_t r0, uint32_t bl_addr) {
+ __asm volatile (
+ "ldr r2, [r1, #0]\n" // get address of stack pointer
+ "msr msp, r2\n" // set stack pointer
+ "ldr r2, [r1, #4]\n" // get address of destination
+ "bx r2\n" // branch to application
+ );
+ MP_UNREACHABLE;
+}
+
+static void try_enter_application(int reset_mode) {
+ uint32_t msp = *(volatile uint32_t*)APPLICATION_ADDR;
+ if ((msp & APP_VALIDITY_BITS) != 0) {
+ // Application is invalid.
+ return;
+ }
+
+ // undo our DFU settings
+ // TODO probably should disable all IRQ sources first
+ #if defined(MBOOT_BOARD_CLEANUP)
+ MBOOT_BOARD_CLEANUP(reset_mode);
+ #endif
+ #if USE_CACHE && defined(STM32F7)
+ SCB_DisableICache();
+ SCB_DisableDCache();
+ #endif
+
+ // Jump to the application.
+ branch_to_application(reset_mode, APPLICATION_ADDR);
+}
+
+static void leave_bootloader(void) {
+ #if !MBOOT_LEAVE_BOOTLOADER_VIA_RESET
+ // Try to enter the application via a jump, if it's valid.
+ try_enter_application(BOARDCTRL_RESET_MODE_BOOTLOADER);
+ #endif
+ NVIC_SystemReset();
+}
+
 static void do_reset(void) {
  led_state_all(0);
  mp_hal_delay_ms(50);
@@ -1337,7 +1381,7 @@ static void do_reset(void) {
  i2c_slave_shutdown(MBOOT_I2Cx, I2Cx_EV_IRQn);
  #endif
  mp_hal_delay_ms(50);
- NVIC_SystemReset();
+ leave_bootloader();
 }
 
 extern PCD_HandleTypeDef pcd_fs_handle;
@@ -1402,17 +1446,11 @@ void stm32_main(int initial_r0) {
  }
 
  int reset_mode = get_reset_mode();
- uint32_t msp = *(volatile uint32_t*)APPLICATION_ADDR;
- if (reset_mode != BOARDCTRL_RESET_MODE_BOOTLOADER && (msp & APP_VALIDITY_BITS) == 0) {
- // not DFU mode so jump to application, passing through reset_mode
- // undo our DFU settings
- // TODO probably should disable all IRQ sources first
- #if USE_CACHE && defined(STM32F7)
- SCB_DisableICache();
- SCB_DisableDCache();
- #endif
- __set_MSP(msp);
- ((void (*)(uint32_t)) *((volatile uint32_t*)(APPLICATION_ADDR + 4)))(reset_mode);
+ if (reset_mode != BOARDCTRL_RESET_MODE_BOOTLOADER) {
+ // Bootloader mode was not selected so try to enter the application,
+ // passing through the reset_mode. This will return if the application
+ // is invalid.
+ try_enter_application(reset_mode);
  }
 
 enter_bootloader:
@@ -1461,7 +1499,7 @@ void stm32_main(int initial_r0) {
  }
  // Always reset because the application is expecting to resume
  led_state_all(0);
- NVIC_SystemReset();
+ leave_bootloader();
  }
  #endif