.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

===============
C2 port support
===============

(C) Copyright 2007 Rodolfo Giometti <giometti@enneenne.com>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.


Overview
--------

This driver implements the support for Linux of Silicon Labs (Silabs)
C2 Interface used for in-system programming of micro controllers.

By using this driver you can reprogram the in-system flash without EC2
or EC3 debug adapter. This solution is also useful in those systems
where the micro controller is connected via special GPIOs pins.

References
----------

The C2 Interface main references are at (https://www.silabs.com)
Silicon Laboratories site], see:

- AN127: FLASH Programming via the C2 Interface at
  https://www.silabs.com/Support Documents/TechnicalDocs/an127.pdf

- C2 Specification at
  https://www.silabs.com/pages/DownloadDoc.aspx?FILEURL=Support%20Documents/TechnicalDocs/an127.pdf&src=SearchResults

however it implements a two wire serial communication protocol (bit
banging) designed to enable in-system programming, debugging, and
boundary-scan testing on low pin-count Silicon Labs devices. Currently
this code supports only flash programming but extensions are easy to
add.

Using the driver
----------------

Once the driver is loaded you can use sysfs support to get C2port's
info or read/write in-system flash::

  # ls /sys/class/c2port/c2port0/
  access            flash_block_size  flash_erase       rev_id
  dev_id            flash_blocks_num  flash_size        subsystem/
  flash_access      flash_data        reset             uevent

Initially the C2port access is disabled since you hardware may have
such lines multiplexed with other devices so, to get access to the
C2port, you need the command::

  # echo 1 > /sys/class/c2port/c2port0/access

after that you should read the device ID and revision ID of the
connected micro controller::

  # cat /sys/class/c2port/c2port0/dev_id
  8
  # cat /sys/class/c2port/c2port0/rev_id
  1

However, for security reasons, the in-system flash access in not
enabled yet, to do so you need the command::

  # echo 1 > /sys/class/c2port/c2port0/flash_access

After that you can read the whole flash::

  # cat /sys/class/c2port/c2port0/flash_data > image

erase it::

  # echo 1 > /sys/class/c2port/c2port0/flash_erase

and write it::

  # cat image > /sys/class/c2port/c2port0/flash_data

after writing you have to reset the device to execute the new code::

  # echo 1 > /sys/class/c2port/c2port0/reset