fix(can): Wait for a free slot in the TX message fifo before trying s…

…ending. (#243)

* Wait for a free slot in the TX message fifo before trying sending.

* minimal delay while waiting for fifo space.

* vTaskDelay

can/firmware/hal_can.c

@@ -100,6 +100,12 @@ void can_send_message(HAL_CAN_HANDLE handle, uint32_t arbitration_id, uint8_t* b
         .TxEventFifoControl = FDCAN_NO_TX_EVENTS,
         .MessageMarker=0
     };
+
+    // Wait for there to be room.
+    while (HAL_FDCAN_GetTxFifoFreeLevel(handle) == 0) {
+        vTaskDelay(1);
+    }
+
     HAL_FDCAN_AddMessageToTxFifoQ(handle, &tx_header, buffer);
 }