Hopefully fix EV3 IR sensor communication breakdown

micropython/modules/ev3_sensors/ev3_sensor.c

@@ -101,6 +101,7 @@ bool ev3_sensor_refresh(repeating_timer_t *rt) {
     if (sensor_id_or_error >= 0) { // got sync!
       link->sensor_metadata.id = sensor_id_or_error;
       link->state = EV3_PROCESSING_HANDSHAKE;
+      link->packetizer.ir_sensor_workaround = sensor_id_or_error == EV3_INFRA_SENSOR_ID;
     }
   }
   if (link->state == EV3_PROCESSING_HANDSHAKE) {

micropython/modules/ev3_sensors/messages.h

@@ -151,6 +151,10 @@ enum {
   // Confirmation that the brick received all sensor information
   EV3_MSG_ACK = (MTYPE_SYSTEM << EV3_MESSAGE_TYPE_SHIFT) |
                 (MTYPE_SYSTEM_ACK << EV3_MESSAGE_SUBTYPE_SHIFT),
+  // Obsolete message sent by the EV3 IR sensor. Early in the EV3
+  // development process it might've been used for checking baud rate sync
+  EV3_MSG_SYNC = (MTYPE_SYSTEM << EV3_MESSAGE_TYPE_SHIFT) |
+                 (MTYPE_SYSTEM_SYNC << EV3_MESSAGE_SUBTYPE_SHIFT),
   // First byte of the sensor handshake
   EV3_INITIAL_MSG = (MTYPE_COMMAND << EV3_MESSAGE_TYPE_SHIFT) |
                     (MTYPE_COMMAND_TYPE << EV3_MESSAGE_SUBTYPE_SHIFT) |

micropython/modules/ev3_sensors/stream_packetizer.c

@@ -16,6 +16,7 @@ void packetizer_reset(packetizer_state *st) {
   st->message.total_size = 0;
   st->message.buffer = st->buffer;
   st->waiting_for_header = true;
+  st->ir_sensor_workaround = false;
 }
 
 void packetizer_poll(packetizer_state *st, opencube_uart_if *uart) {
@@ -26,6 +27,10 @@ void packetizer_poll(packetizer_state *st, opencube_uart_if *uart) {
 
     if (try_complete_message(st, uart) == DONE) {
       st->waiting_for_header = true;
+      if (st->ir_sensor_workaround && st->message.buffer[0] == EV3_MSG_SYNC) {
+        // skip broken SYNC packets from EV3 IR sensor
+        continue;
+      }
       if (st->callback(st->callback_context, st->message.buffer, st->message.total_size) == PROC_STOP) {
         break;
       }
@@ -45,10 +50,18 @@ completion try_read_header(packetizer_state *st, opencube_uart_if *uart) {
   }
 
   st->message.buffer[0] = header;
-  st->message.total_size = full_length_of_message(header);
   st->message.done_size = 1;
-  if (st->message.total_size > EV3_MSG_BUFFER_SIZE) {
-    st->message.total_size = EV3_MSG_BUFFER_SIZE;
+
+  if (st->ir_sensor_workaround && header == EV3_MSG_SYNC) {
+    // The IR sensor sometimes sends 0x00 0xFF packets during the
+    // handshake - they look like broken SYNC packages. They are useless,
+    // so just detect them here and later skip them
+    st->message.total_size = 2;
+  } else {
+    st->message.total_size = full_length_of_message(header);
+    if (st->message.total_size > EV3_MSG_BUFFER_SIZE) {
+      st->message.total_size = EV3_MSG_BUFFER_SIZE;
+    }
   }
   return DONE;
 }

micropython/modules/ev3_sensors/stream_packetizer.h

@@ -26,6 +26,7 @@ typedef struct {
   partial_message message;
   uint8_t buffer[EV3_MSG_BUFFER_SIZE];
   bool waiting_for_header;
+  bool ir_sensor_workaround;
 } packetizer_state;
 
 /**