Deleting superflous call to 'usbd.epBank0ResetReady' - this function is already called within 'USBDeviceClass::ISRHandler' and 'USBDeviceClass::recvControl' is called by 'handleClassInterfaceSetup' within the ISR

Bugfix - removal of delay within USBDeviceClass::ISRHandler
- remove stall requests of endpoint #0 OUT (bank #0) if present
- copy data from cache into structure instead of referencing it via pointer. When referencing via pointer the content of the structure can change if new data is written to the buffer.
- Fixing MULTI_PACKET_SIZE parameter of call to 'usbd.epBank0SetMultiPacketSize' within 'USBDeviceClass::armRecvCtrlOUT' to correct size, MULTI_PACKET_SIZE should not be set to a value < SIZE, this means at least to 64.
- resetting byte count for endpoint #0 seems to eliminate issue of the bootloader not being triggered.

Author: aentinger

cores/arduino/USB/USBCore.cpp

@@ -469,9 +469,6 @@ uint32_t USBDeviceClass::recvControl(void *_data, uint32_t len)
 {
 	uint8_t *data = reinterpret_cast<uint8_t *>(_data);
 
-	// The RAM Buffer is empty: we can receive data
-	usbd.epBank0ResetReady(0);
-
 	//usbd.epBank0AckSetupReceived(0);
 	uint32_t read = armRecvCtrlOUT(0);
 	if (read > len)
@@ -551,7 +548,17 @@ uint8_t USBDeviceClass::armRecvCtrlOUT(uint32_t ep)
 {
 	// Get endpoint configuration from setting register
 	usbd.epBank0SetAddress(ep, &udd_ep_out_cache_buffer[ep]);
-	usbd.epBank0SetMultiPacketSize(ep, 8);
+	/* Atmel-42181G–SAM-D21_Datasheet–09/2015 / Page 806
+	 *
+	 * For OUT endpoints, MULTI_PACKET_SIZE holds the total
+	 * data size for the complete transfer. This value must
+	 * be a multiple of the maximum packet size.
+	 *
+	 * Since SIZE is 64 (see 'USBDeviceClass::initEP') for
+	 * all endpoints MULTI_PACKET_SIZE should not be set to
+	 * a value < SIZE, this means at least to 64.
+	 */
+	usbd.epBank0SetMultiPacketSize(ep, 64);
 	usbd.epBank0SetByteCount(ep, 0);
 
 	usbd.epBank0ResetReady(ep);
@@ -830,23 +837,34 @@ void USBDeviceClass::ISRHandler()
 #endif
 	}
 
+	/* Remove any stall requests for endpoint #0 */
+	if (usbd.epBank0IsStalled(0)) { usbd.epBank0DisableStalled(0); }
+
 	// Endpoint 0 Received Setup interrupt
 	if (usbd.epBank0IsSetupReceived(0))
 	{
-		USBSetup *setup = reinterpret_cast<USBSetup *>(udd_ep_out_cache_buffer[0]);
-
-		delayMicroseconds(20);
-		/* Clear the Bank 0 ready flag on Control OUT */
-		// The RAM Buffer is empty: we can receive data
+		/* Retrieve received endpoint #0 data from buffer */
+		USBSetup setup;
+		memcpy(&setup, udd_ep_out_cache_buffer[0], sizeof(USBSetup));
+
+		/* Tell the USB hardware that we are ready to receive more data for endpoint #0 and also reset the byte count
+		 * for endpoint #0 - the clearing seems to be necessary for the code to function correctly, although the datasheet
+		 * is not clear on the subject.
+		 *
+		 * Atmel-42181G–SAM-D21_Datasheet–09/2015 / Page 806
+		 *   For IN endpoints, BYTE_COUNT holds the number of bytes to be sent in the next IN transaction.
+		 *   For OUT endpoint or SETUP endpoints, BYTE_COUNT holds the number of bytes received upon the last OUT or SETUP transaction.
+		 */
+		usbd.epBank0SetByteCount(0, 0);
 		usbd.epBank0ResetReady(0);
 
 		bool ok;
-		if (REQUEST_STANDARD == (setup->bmRequestType & REQUEST_TYPE)) {
+		if (REQUEST_STANDARD == (setup.bmRequestType & REQUEST_TYPE)) {
 			// Standard Requests
-			ok = handleStandardSetup(*setup);
+			ok = handleStandardSetup(setup);
 		} else {
 			// Class Interface Requests
-			ok = handleClassInterfaceSetup(*setup);
+			ok = handleClassInterfaceSetup(setup);
 		}
 
 		if (ok) {