Yet Another YModem

This project was born out of a need to have an implementation of YModem that was suitable for bare-metal embedded environments and that had a license that would allow it to be used freely.

Implemntation

This implementation is based on the XMODEM/YMODEM PROTOCOL REFERENCE specification document.
From this document, the following sequence diagram was made:

The organization of the code takes into account this diagram.

CRC

CRC sources are in ymodem/crc and were generated using pycrc.

Sources were created using the following algorithms:

• bit-by-bit: slowest but simpler and smallest algoritm, It compute CRC bit by bit
• bit-by-bit-fast: like bit-by-bit it compute CRC bit by bit, but is a little faster and not so small.
• table-driven: fastest algorithm but also bigger.

The user will be able to choose which of the 3 algorithms to use based on the environment of constraints he will have.

Usage

The only thing you have to do to integrate YAYModem into your project is to customize the ymodem_port.* files.
You also have to provide some other function as callbacks.

Find examples in the test directory.

ry

In the test/ry directory you will find a ymodem receiver implementation. In the same directory you will also find a customization of ymodem_port.* files.
To test it, socat is used to create pty serial devices:

• In terminal 1:

  socat pty,raw,echo=0,link=/tmp/ttyV1 pty,raw,echo=0,link=/tmp/ttyV2
  

  this command creates two devices /tmp/ttyV1 and /tmp/ttyV2 connected together by socat.

• In terminal 2:

  test/ry/ry </tmp/ttyV2 >/tmp/ttyV2
  

  this receives files through /tmp/ttyV2

• In terminal 3:

  sb -b --ymodem some_file </tmp/ttyV1 >/tmp/ttyV1
  

  this sends the some_file through /tmp/ttyV1

TODO

Currently only reception is implemented. I would like to write sending as well. You can contribute.

License

This project is covered by the Apache 2.0 license