implemented sending prefix and fixed wrong payload length

src/main.cpp

@@ -69,14 +69,18 @@ void loop() {
     counter = 0;
 
     // Mirror data via Serial
+    Serial.print("Received raw integers: ");
     while (bytesAvailable--) {
-      char currentByte = (char)RawHID.read();
+      int currentByte = RawHID.read();
+      Serial.print(currentByte);
+      Serial.print(" ");
       // save only if it is a printable character
       if(currentByte >= 32 && currentByte <= 126) 
       {
         receivedMessageBuffer[counter++] = currentByte;
       }
     }
+    Serial.print("\n");
 
     // print read message
     Serial.print("Received: '");
@@ -128,7 +132,7 @@ void UsbHidSendLine(unsigned char* str)
   if (str!=NULL) {
     int32_t messageBytes = McuUtility_strlen((char*)str);
     uint8_t bufferSize = sizeof(sendMessageBuffer);
-    uint8_t numBytesPerMessage = bufferSize - 1;  // last byte got omitted always, therefore it is not sent
+    uint8_t maxNumBytesPerMessage = bufferSize - 2;  // 1 because last byte got omitted always (therefore it is not sent), 2 because of prefix
     Serial.print("Sending message with ");
     Serial.print(messageBytes);
     Serial.print(" bytes and buffer size ");
@@ -138,11 +142,16 @@ void UsbHidSendLine(unsigned char* str)
     // split message in buffer Size amount
     for(int messageNum = 0; messageBytes > 0; messageNum++){
       memset(sendMessageBuffer, '\0', sizeof(sendMessageBuffer));  // clear send buffer
-      // copy part of message to send buffer. move pointer by buffer size to take the next part of the string.
-      McuUtility_strcpy((unsigned char*)sendMessageBuffer, numBytesPerMessage, (unsigned char*)(str + (numBytesPerMessage*messageNum)));  
+      // calculate length of payload
+      uint8_t payloadLength = messageBytes > maxNumBytesPerMessage ? maxNumBytesPerMessage : messageBytes;
+      // prefix: 0=report ID, 1=amount of bytes for this payload, rest=payload
+      sendMessageBuffer[0] = 0x00;
+      sendMessageBuffer[1] = payloadLength;
+      // copy part of message to send buffer. move pointer by buffer size to take the next part of the string. (offset destination pointer by 2 because of prefix)
+      McuUtility_strcpy(((unsigned char*)sendMessageBuffer) + 2, maxNumBytesPerMessage+1, (unsigned char*)(str + (maxNumBytesPerMessage*messageNum)));  
       RawHID.write(sendMessageBuffer, sizeof(sendMessageBuffer));  // write buffer
       Serial.print((char*)sendMessageBuffer);  // print
-      messageBytes -= numBytesPerMessage;  // subtract numBytes that were sent from message bytes
+      messageBytes -= maxNumBytesPerMessage;  // subtract numBytes that were sent from message bytes
     }
 
     Serial.print("\n'''\n");