Implemented automatic retry when reading registers.

Automatically retry reading registers a few times if the CRC doesn't match.

Author: pvginkel

src/TMC2209.h

@@ -285,7 +285,7 @@ class TMC2209
   const static uint8_t STEPPER_DRIVER_FEATURE_OFF = 0;
   const static uint8_t STEPPER_DRIVER_FEATURE_ON = 1;
 
-  const static int MAX_READ_RETRIES = 5;
+  const static uint8_t MAX_READ_RETRIES = 5;
   const static uint32_t READ_RETRY_DELAY_MS = 20;
 
   // Datagrams

src/TMC2209/TMC2209.cpp

@@ -916,32 +916,43 @@ uint32_t TMC2209::read(uint8_t register_address)
   read_request_datagram.rw = RW_READ;
   read_request_datagram.crc = calculateCrc(read_request_datagram, READ_REQUEST_DATAGRAM_SIZE);
 
-  sendDatagramBidirectional(read_request_datagram, READ_REQUEST_DATAGRAM_SIZE);
-
-  uint32_t reply_delay = 0;
-  while ((serialAvailable() < WRITE_READ_REPLY_DATAGRAM_SIZE) and
-    (reply_delay < REPLY_DELAY_MAX_MICROSECONDS))
+  for (uint8_t retry = 0; retry < MAX_READ_RETRIES; retry++)
   {
-    delayMicroseconds(REPLY_DELAY_INC_MICROSECONDS);
-    reply_delay += REPLY_DELAY_INC_MICROSECONDS;
-  }
+    sendDatagramBidirectional(read_request_datagram, READ_REQUEST_DATAGRAM_SIZE);
 
-  if (reply_delay >= REPLY_DELAY_MAX_MICROSECONDS)
-  {
-    return 0;
-  }
+    uint32_t reply_delay = 0;
+    while ((serialAvailable() < WRITE_READ_REPLY_DATAGRAM_SIZE) and
+      (reply_delay < REPLY_DELAY_MAX_MICROSECONDS))
+    {
+      delayMicroseconds(REPLY_DELAY_INC_MICROSECONDS);
+      reply_delay += REPLY_DELAY_INC_MICROSECONDS;
+    }
 
-  uint64_t byte;
-  uint8_t byte_count = 0;
-  WriteReadReplyDatagram read_reply_datagram;
-  read_reply_datagram.bytes = 0;
-  for (uint8_t i=0; i<WRITE_READ_REPLY_DATAGRAM_SIZE; ++i)
-  {
-    byte = serialRead();
-    read_reply_datagram.bytes |= (byte << (byte_count++ * BITS_PER_BYTE));
+    if (reply_delay >= REPLY_DELAY_MAX_MICROSECONDS)
+    {
+      return 0;
+    }
+
+    uint64_t byte;
+    uint8_t byte_count = 0;
+    WriteReadReplyDatagram read_reply_datagram;
+    read_reply_datagram.bytes = 0;
+    for (uint8_t i=0; i<WRITE_READ_REPLY_DATAGRAM_SIZE; ++i)
+    {
+      byte = serialRead();
+      read_reply_datagram.bytes |= (byte << (byte_count++ * BITS_PER_BYTE));
+    }
+
+    auto crc = calculateCrc(read_reply_datagram, WRITE_READ_REPLY_DATAGRAM_SIZE);
+    if (crc == read_reply_datagram.crc)
+    {
+      return reverseData(read_reply_datagram.data);
+    }
+
+    delay(READ_RETRY_DELAY_MS);
   }
 
-  return reverseData(read_reply_datagram.data);
+  return 0;
 }
 
 uint8_t TMC2209::percentToCurrentSetting(uint8_t percent)