Port AVR Serial_::readBreak() API to SAM core

Author: sandeepmistry

cores/arduino/USB/CDC.cpp

@@ -55,6 +55,8 @@ static volatile LineInfo _usbLineInfo = {
  0x00 // lineState
 };
 
+static volatile int32_t breakValue = -1;
+
 _Pragma("pack(1)")
 static const CDCDescriptor _cdcInterface =
 {
@@ -144,6 +146,7 @@ bool WEAK CDC_Setup(USBSetup& setup)
 
 if (CDC_SEND_BREAK == r)
 {
+breakValue = ((uint16_t)setup.wValueH << 8) | setup.wValueL;
 return true;
 }
 }
@@ -305,6 +308,28 @@ Serial_::operator bool()
 return result;
 }
 
+int32_t Serial_::readBreak() {
+uint8_t enableInterrupts = ((__get_PRIMASK() & 0x1) == 0 && 
+(__get_FAULTMASK() & 0x1) == 0);
+
+// disable interrupts,
+// to avoid clearing a breakValue that might occur 
+// while processing the current break value
+__disable_irq();
+
+int ret = breakValue;
+
+breakValue = -1;
+
+if (enableInterrupts)
+{
+// re-enable the interrupts
+__enable_irq();
+}
+
+return ret;
+}
+
 unsigned long Serial_::baud() {
 return _usbLineInfo.dwDTERate;
 }

cores/arduino/USB/USBAPI.h

@@ -63,6 +63,23 @@ class Serial_ : public Stream
 using Print::write; // pull in write(str) from Print
 operator bool();
 
+// This method allows processing "SEND_BREAK" requests sent by
+// the USB host. Those requests indicate that the host wants to
+// send a BREAK signal and are accompanied by a single uint16_t
+// value, specifying the duration of the break. The value 0
+// means to end any current break, while the value 0xffff means
+// to start an indefinite break.
+// readBreak() will return the value of the most recent break
+// request, but will return it at most once, returning -1 when
+// readBreak() is called again (until another break request is
+// received, which is again returned once).
+// This also mean that if two break requests are received
+// without readBreak() being called in between, the value of the
+// first request is lost.
+// Note that the value returned is a long, so it can return
+// 0-0xffff as well as -1.
+int32_t readBreak();
+
 // These return the settings specified by the USB host for the
 // serial port. These aren't really used, but are offered here
 // in case a sketch wants to act on these settings.