lxterm: Don't attempt to recover from CRC errors during upload.

This allows transfers to proceed at the full speed of the serial link.
We still check all responses, but will now fail outright if a CRC error
occurs.

litex/tools/litex_term.py

@@ -203,6 +203,19 @@ def send_frame(self, frame):
                 retry = 0
         return 1
 
+    def receive_upload_response(self):
+        # If we're not doing CRC checking, then there's no response to read.
+        if self.no_crc:
+            return
+        reply = self.port.read()
+        if reply == sfl_ack_success:
+            return
+        elif reply == sfl_ack_crcerror:
+            print("[LXTERM] Upload to device failed due to data corruption (CRC error)")
+        else:
+            print(f"[LXTERM] Got unexpected response from device '{reply}'")
+        sys.exit(1)
+
     def upload(self, filename, address):
         f = open(filename, "rb")
         f.seek(0, 2)
@@ -214,6 +227,7 @@ def upload(self, filename, address):
         position = 0
         start = time.time()
         remaining = length
+        outstanding = 0
         while remaining:
             sys.stdout.write("|{}>{}| {}%\r".format('=' * (20*position//length),
                                                     ' ' * (20-20*position//length),
@@ -227,12 +241,17 @@ def upload(self, filename, address):
                 frame.cmd = sfl_cmd_load if not self.no_crc else sfl_cmd_load_no_crc
             frame.payload = current_address.to_bytes(4, "big")
             frame.payload += frame_data
-            if self.send_frame(frame) == 0:
-                return
+            self.port.write(frame.encode())
+            outstanding += 1
+            if self.port.in_waiting:
+                self.receive_upload_response()
+                outstanding -= 1
             current_address += len(frame_data)
             position += len(frame_data)
             remaining -= len(frame_data)
             time.sleep(1e-5) # Inter-frame delay for fast UARTs (ex: FT245).
+        for _ in range(outstanding):
+            self.receive_upload_response()
         end = time.time()
         elapsed = end - start
         f.close()