COBS - Consistent Overhead Byte Stuffing

Very nice and simple protocol

See https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing

The cobs idea

The basic idea behind cobs is to have a binary protocol with minimized stuffing overhead.

The overhead is only 1 or 2 bytes. The limitation is that the lenght of one package is 254 bytes.

There is no fail detection or cerrection in the cobs protocol itself.

For that reason a CRC-16 checksum detection has been coded and is given below.

Download an Arduino impl here

An example

Just an example

• cobs.h

• cobs.cpp

• cobstest.ino

With crc16

• cobscrc16tst.ino test

CRC16 library code

A small note: The CRC16 code below is targeted to an Arduino UNO. So the CRC table is located in code memory. It is easy to change to be located in normale data memory.

• crc16.zip

• crc16.cpp

• crc16.h

• crctest.ino

and the arduino PROGMEM version

• crc16ard.h

• crc16ard.cpp

• crc16ardtest.ino

The easiest way to use a CRC16 might just be install the Arduino CRC library by Rob Tillaart3

NB NB CRC16 NB NB A CRC16 is not just a CRC16 cheksum.

There is a generator polynomial attached so you can have different implementations of CRC16 is not compatible is they used different generator polynomials.

• See a multi polynominal CRC16 implementation here

• Another CRC16 calculator https://www.tutorialspoint.com/cyclic-redundancy-check-crc-in-arduino

  • based on the Fletchers checksum https://en.wikipedia.org/wiki/Fletcher%27s_checksum

“THE BEER-WARE LICE NSE” (Revision 42): jensd@jensd.dk wrote this file. As long as you retain this notice you can do whatever you want with this stuff on these pages. If we meet some day, and you think this stuff is worth it, you can buy me a beer in return :-)
(C) Jens Dalsgaard Nielsen
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