tjtag-pi2 is a slightly modified version of tjtag-pi which adds support for the nTRST pin used on some devices.

Tested on an Atheros AR531X board with EJTAG 2.6 interface - works fine, both the device and the flash chip is detected through the JTAG interface.

WARNING

Be warned that incorrect usage can lead to a point of no return situation. Before you do anything besides what is described here, please do research on how to use this tool. A good starting point is the excellent and cautionary guide.pdf written by the HairyDairyMaid, the original author. Always backup before flashing.

Requirements

• A Raspberry Pi (I've only tested model B as of late 2013)
• Dual female jumper wires to connect GPIO pins to the board
• Pins soldered on the JTAG header of the target device
• Beverege to enjoy afterward

Setup

1. Hook up the two boards as per the diagram in wiring.jpg

2. Optionally, bridge GPIO8 pin on the Pi to the nTRST pin on your device

3. Power up your device

4. Checkout the code, compile and run it

   $ cd ~
   $ git clone https://github.com/kissg1988/tjtag-pi2.git
   $ cd tjtag-pi2
   $ make pi
   $ ./tjtag -probeonly
   

   If it gets stuck, try using /noemw option.

If at this point, your SoC and flash is recognized, you're all set. Enjoy your beverage and look for an appropriate guide that explains how to use tjtag to revive/upgrade your device's firmware.

Notes

• If you have issues with reliability of your connection, you can slow down the speed of tjtag by using /delay:N command line option. N is the amount of time to delay flipping the clock signal. The higher the value, the slower the transfer rate.
• Due to bit-banging nature of the operation of tjtag, various things affect the transfer speed. The one with most degrading effect is the progress output. Therefore it is recommended to use /silent command line option and redirect outputs to /dev/null (ie using &> /dev/null), after having made sure everything works OK.