SerialTransfer

Arduino library (available through the Arduino IDE's Libraries Manager!) to transfer packetized data fast/reliably via UART/Serial. A mirror library is also available for Python!

This library:

• can be downloaded via the Arduino IDE's Libraries Manager (search "SerialTransfer.h")
• works with "software-serial" libraries
• is non blocking
• uses packet delimiters
• uses consistent overhead byte stuffing
• uses CRC-8 (Polynomial 0x9B with lookup table)
• allows the use of dynamically sized packets (packets can have payload lengths anywhere from 1 to 254 bytes)
• can transfer bytes, ints, floats, structs, even large files like JPEGs!!

Packet Anatomy:

01111110 11111111 00000000 00000000 00000000 ... 00000000 10000001
|      | |      | |      | |      | |      | | | |      | |______|__Stop byte
|      | |      | |      | |      | |      | | | |______|___________8-bit CRC
|      | |      | |      | |      | |      | |_|____________________Rest of payload
|      | |      | |      | |      | |______|________________________2nd payload byte
|      | |      | |      | |______|_________________________________1st payload byte
|      | |      | |______|__________________________________________# of payload bytes
|      | |______|___________________________________________________COBS Overhead byte
|______|____________________________________________________________Start byte (constant)

How To Use:

Both Arduinos:

1.) Include the library and create a Serial Transfer class instance:

#include "SerialTransfer.h"
SerialTransfer myTransfer;

2.) Determine which serial ports the transfer will occur on and initialize it:

Serial1.begin(115200);

3.) Pass the SerialX class to the SerialTransfer class for initialization:

myTransfer.begin(Serial1);

Transmitting Arduino:

1.) Insert data bytes into the SerialTransfer TX buffer:

myTransfer.txBuff[0] = 'h';
myTransfer.txBuff[1] = 'i';
myTransfer.txBuff[2] = '\n';

2.) Transmit the data via the "sendData" member function. The argument of sendData() is the number of bytes of the TX buffer to be transmitted. Since we stuffed 3 data bytes ('h', 'i', and '\n') into the TX buffer, we need to specify 3 bytes to be transferred:

myTransfer.sendData(3);

Complete TX Code:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  myTransfer.txBuff[0] = 'h';
  myTransfer.txBuff[1] = 'i';
  myTransfer.txBuff[2] = '\n';
  
  myTransfer.sendData(3);
  delay(100);
}

Receiving Arduino:

1.) Repetitively check to see if a new packet has been completely received. Also, check to see if any transfer errors have occurred:

if(myTransfer.available())
{
  // see next step
}
else if(myTransfer.status < 0)
{
  Serial.print("ERROR: ");

  if(myTransfer.status == -1)
    Serial.println(F("CRC_ERROR"));
  else if(myTransfer.status == -2)
    Serial.println(F("PAYLOAD_ERROR"));
  else if(myTransfer.status == -3)
    Serial.println(F("STOP_BYTE_ERROR"));
}

2.) If a full packet has been received, use the SerialTransfer class's RX buffer to access the received data bytes:

Serial.println("New Data");
for(byte i = 0; i < myTransfer.bytesRead; i++)
  Serial.write(myTransfer.rxBuff[i]);
Serial.println();

Complete RX Code:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  if(myTransfer.available())
  {
    Serial.println("New Data");
    for(byte i = 0; i < myTransfer.bytesRead; i++)
      Serial.write(myTransfer.rxBuff[i]);
    Serial.println();
  }
  else if(myTransfer.status < 0)
  {
    Serial.print("ERROR: ");

    if(myTransfer.status == -1)
      Serial.println(F("CRC_ERROR"));
    else if(myTransfer.status == -2)
      Serial.println(F("PAYLOAD_ERROR"));
    else if(myTransfer.status == -3)
      Serial.println(F("STOP_BYTE_ERROR"));
  }
}