Fixed write() freezing entire Sketch unless MIDI port is opened by PC

multiple architecture version
fixes #4

Author: odbol

src/MIDIUSB.cpp

@@ -153,14 +153,23 @@ size_t MIDI_::write(const uint8_t *buffer, size_t size)
 	// open connection isn't broken cleanly (cable is yanked out, host dies
 	// or locks up, or host virtual serial port hangs)
 
-	int r = USB_Send(MIDI_TX, buffer, size);
-
-	if (r > 0)
-	{
-		return r;
-	} else
+	// first, check the TX buffer to see if it's ready for writing.
+	// USB_Send() may block if there's no one listening on the other end.
+	// in that case, we don't want to block waiting for someone to connect,
+	// because that would freeze the whole sketch
+	// instead, we'll just drop the packets and hope the caller figures it out.
+	if (is_write_enabled(MIDI_TX))
 	{
-		return 0;
+
+		int r = USB_Send(MIDI_TX, buffer, size);
+
+		if (r > 0)
+		{
+			return r;
+		} else
+		{
+			return 0;
+		}
 	}
 	return 0;
 }

src/MIDIUSB.h

@@ -33,6 +33,7 @@ typedef struct
 #define EP_TYPE_BULK_OUT_MIDI		EP_TYPE_BULK_OUT
 #define EP_TYPE_BULK_IN_MIDI		EP_TYPE_BULK_IN
 #define MIDI_BUFFER_SIZE			64
+#define is_write_enabled(x)			(1)
 
 #else
 
@@ -41,11 +42,12 @@ typedef struct
 #define MIDI_BUFFER_SIZE			512
 
 #if defined(ARDUINO_ARCH_SAM)
-#define USB_SendControl 	USBD_SendControl
-#define USB_Available 		USBD_Available
-#define USB_Recv 			USBD_Recv
-#define USB_Send 			USBD_Send
-#define USB_Flush 			USBD_Flush
+#define USB_SendControl         USBD_SendControl
+#define USB_Available           USBD_Available
+#define USB_Recv                USBD_Recv
+#define USB_Send                USBD_Send
+#define USB_Flush               USBD_Flush
+#define is_write_enabled(x)     Is_udd_write_enabled(x)
 
 #define EP_TYPE_BULK_IN_MIDI		(UOTGHS_DEVEPTCFG_EPSIZE_512_BYTE | \
 									UOTGHS_DEVEPTCFG_EPDIR_IN |         \
@@ -62,11 +64,12 @@ typedef struct
 #endif
 
 #if defined(__SAMD21G18A__)
-#define USB_SendControl		USBDevice.sendControl
-#define USB_Available		USBDevice.available
-#define USB_Recv 			USBDevice.recv
-#define USB_Send 			USBDevice.send
-#define USB_Flush 			USBDevice.flush
+#define USB_SendControl         USBDevice.sendControl
+#define USB_Available           USBDevice.available
+#define USB_Recv                USBDevice.recv
+#define USB_Send                USBDevice.send
+#define USB_Flush               USBDevice.flush
+#define is_write_enabled(x)     (1)
 
 #define EP_TYPE_BULK_IN_MIDI 		USB_ENDPOINT_TYPE_BULK | USB_ENDPOINT_IN(0);
 #define EP_TYPE_BULK_OUT_MIDI 		USB_ENDPOINT_TYPE_BULK | USB_ENDPOINT_OUT(0);