Autoreset 1200 bps fix.

1 files changed, 15 insertions, 2 deletions

diff --git a/cores/arduino/CDC.cpp b/cores/arduino/CDC.cpp
index 7f33a6e..6d3929e 100644
--- a/cores/arduino/CDC.cpp
+++ b/cores/arduino/CDC.cpp
@@ -101,13 +101,26 @@ bool WEAK CDC_Setup(Setup& setup)
 		if (CDC_SET_CONTROL_LINE_STATE == r)
 		{
 			_usbLineInfo.lineState = setup.wValueL;
+
 			// auto-reset into the bootloader is triggered when the port, already 
 			// open at 1200 bps, is closed.  this is the signal to start the watchdog
 			// with a relatively long period so it can finish housekeeping tasks
 			// like servicing endpoints before the sketch ends
-			if (0 != _usbLineInfo.lineState && 1200 == _usbLineInfo.dwDTERate) {
+
+			// We check DTR state to determine if host port is open (bit 0 of lineState).
+			// Serial1.print(">"); Serial1.println(_usbLineInfo.lineState, HEX);
+			if ((_usbLineInfo.lineState & 0x01) == 0 && _usbLineInfo.dwDTERate == 1200) {
 				*(uint16_t *)0x0A00 = 0x7777;
 				wdt_enable(WDTO_250MS);
+			} else {
+				// Most OSs do some intermediate steps when configuring ports and DTR can
+				// twiggle more than once before stabilizing.
+				// To avoid spurious resets we set the watchdog to 250ms and eventually
+				// cancel if DTR goes back high.
+
+				wdt_disable();
+				wdt_reset();
+				*(uint16_t *)0x0A00 = 0x0;
 			}
 			return true;
 		}
@@ -202,4 +215,4 @@ size_t Serial_::write(uint8_t c)
 Serial_ Serial;
 
 #endif
-#endif /* if defined(USBCON) */
\ No newline at end of file
+#endif /* if defined(USBCON) */