Add Serial::onUsbSetupPacket() on CDC serial objects

This allows executing an arbitrary callback on receipt on a USB setup
packet on the CDC serial interface. This allows running code directly
when settings change, or handle messages not handled by the Arduino core
(like CDC_SEND_BREAK).

Author: matthijskooijman

hardware/arduino/avr/cores/arduino/CDC.cpp

@@ -31,6 +31,8 @@ typedef struct
 	u8	lineState;
 } LineInfo;
 
+static bool (*on_cdc_setup_packet)(const Setup&) = NULL;
+
 static volatile LineInfo _usbLineInfo = { 57600, 0x00, 0x00, 0x00, 0x00 };
 
 #define WEAK __attribute__ ((weak))
@@ -62,6 +64,8 @@ int WEAK CDC_GetInterface(u8* interfaceNum)
 
 bool WEAK CDC_Setup(Setup& setup)
 {
+	bool result = false;
+
 	u8 r = setup.bRequest;
 	u8 requestType = setup.bmRequestType;
 
@@ -70,7 +74,7 @@ bool WEAK CDC_Setup(Setup& setup)
 		if (CDC_GET_LINE_CODING == r)
 		{
 			USB_SendControl(0,(void*)&_usbLineInfo,7);
-			return true;
+			result = true;
 		}
 	}
 
@@ -111,9 +115,14 @@ bool WEAK CDC_Setup(Setup& setup)
 				*(uint16_t *)0x0800 = 0x0;
 			}
 		}
-		return true;
+		result = true;
 	}
-	return false;
+
+	// Call callback to allow sketch to do additional processing
+	if (on_cdc_setup_packet)
+		return on_cdc_setup_packet(setup) || result;
+	else
+		return result;
 }
 
 
@@ -229,6 +238,10 @@ bool Serial_::rts() {
 	return _usbLineInfo.lineState & 0x2;
 }
 
+void Serial_::onUsbSetupPacket(bool (*func)(const Setup&)) {
+	on_cdc_setup_packet = func;
+}
+
 Serial_ Serial;
 
 #endif

hardware/arduino/avr/cores/arduino/USBAPI.h

@@ -70,6 +70,9 @@ struct ring_buffer;
 #error Please lower the CDC Buffer size
 #endif
 
+// Forward declaration so we can take a reference below:
+struct Setup;
+
 class Serial_ : public Stream
 {
 private:
@@ -115,6 +118,13 @@ class Serial_ : public Stream
 		SPACE_PARITY = 4,
 	};
 
+	// This allows setting a callback for every USB setup packet
+	// received (called after regular processing). If the callback
+	// returns true, the packet will be acknowledged. If the
+	// callback returns false, the regular handling determines the
+	// result. Note that the callback will run in ISR context, so it
+	// should be short and not block.
+	void onUsbSetupPacket(bool (*func)(const Setup&));
 };
 extern Serial_ Serial;