firmware/ev3: allow buggy replies from EV3 bootloader

Add a hack to not fail if the EV3 bootloader sends an echo of the request
instead of the expected response. There is a known compatibility issue
with the EV3 bootloader USB and, e.g. Windows with USB 3.0 ports. This
apparently causes a race condition where commands that don't take long
to process before sending a response will have the request echoed back
instead of receiving the actual response. If this happens, we can
ignore it and assume the command was successful. It just won't work, e.g.
for the version command since that has a payload in the response.

Author: dlech

src/firmware/sagas.ts

@@ -1113,16 +1113,33 @@ function* handleFlashEV3(action: ReturnType<typeof firmwareFlashEV3>): Generator
                 continue; // ignore empty reports
             }
 
-            const length = event.data.getInt16(0, true);
+            let length = event.data.getInt16(0, true);
             const replyNumber = event.data.getInt16(2, true);
-            const messageType = event.data.getUint8(4);
+            let messageType = event.data.getUint8(4);
             const replyCommand = event.data.getUint8(5);
-            const status = event.data.getUint8(6);
-            const payload = event.data.buffer.slice(7, 7 + length + 2);
+            let status = event.data.getUint8(6);
+            let payload = event.data.buffer.slice(7, 7 + length + 2);
+
+            if (messageType === 0x01) {
+                // HACK: This works around a strange bug that can be triggered
+                // e.g. by USB 3.0 on Windows. Sometimes the EV3 bootloader will
+                // send the request back instead of the reply. In this case,
+                // fake the reply to avoid protocol errors. This seems to work
+                // as long as we aren't sending commands that have a reply
+                // with a payload (like reading version or checksum)
+
+                console.warn(
+                    `Bad EV3 reply: length=${length}, replyNumber=${replyNumber}, messageType=${messageType}, replyCommand=${replyCommand}, status=${status}`,
+                );
+                length = 5;
+                messageType = 0x03;
+                status = 0x00;
+                payload = new ArrayBuffer(0);
 
-            console.debug(
-                `EV3 reply: length=${length}, replyNumber=${replyNumber}, messageType=${messageType}, replyCommand=${replyCommand}, status=${status}, payload=${payload}`,
-            );
+                console.info(
+                    `Fixed EV3 reply: length=${length}, replyNumber=${replyNumber}, messageType=${messageType}, replyCommand=${replyCommand}, status=${status}`,
+                );
+            }
 
             yield* put(
                 firmwareDidReceiveEV3Reply(