Inexpensive Ethernet JTAG Adapter with Raspberry Pi and OpenOCD

I recently wanted an ethernet JTAG adapter for a project I was working on. Unfortunately ethernet JTAG adapters can cost upwards of $300, and even then they can be specific to particular chipset and toolchains.

However, were already using OpenOCD with ST-LINK/V2 programmers to communicate with out hardware, and it turns out that it’s very easy to set up OpenOCD on the Raspberry Pi. You can then plug the programmer into the Pi, connect a debugger (gdb in our case) to the OpenOCD instance, and debug your firmware remotely!

The Raspberry Pi is also a very convenient platform for adding additional interfaces to your hardware. For our project, we have FTDI serial cables and some ADC’s connected to ours as well. This lets us flash and debug our hardware, communicate with it over serial (forwarded over a socket), and continuously monitor power consumption of key components on our board. And we can do it from anywhere with an internet connection. It’s basically magic.

1. Acquire a Pi

First you’ll need a Rapsberry Pi and an SD card with the Raspbian installed on it. You can get a Raspberry Model B Starter Kit from Newark. This comes with a power adapter and an SD card with Noobs (which can automatically install Raspbian for you) pre-installed and is probably the easiest way to get started.

2. Install a Recent Version of OpenOCD

There is a version of OpenOCD already in the package database for Raspbian, but it’s version 0.6.1, which was too old for our platform. Fortunately it’s quite easy to install the latest OpenOCD from scratch. There are pretty good instructions on how to do this at SourceForge. But specifically for the Pi you can just do the following:

From your Pi:

sudo apt-get update
sudo apt-get install libtool libusb-dev libusb-1.0 autoconf automake texinfo

And then:

git clone git://git.code.sf.net/p/openocd/code openocd-code
cd openocd-code/
./bootstrap
./configure

This should spit out a bunch of stuff and then if everything worked you should see this at the end:

OpenOCD configuration summary

MPSSE mode of FTDI based devices yes (auto)
ST-Link JTAG Programmer yes (auto)
TI ICDI JTAG Programmer yes (auto)
Keil ULINK JTAG Programmer yes (auto)
Altera USB-Blaster II Compatible yes (auto)
Segger J-Link JTAG Programmer yes (auto)
OSBDM (JTAG only) Programmer yes (auto)
eStick/opendous JTAG Programmer yes (auto)
Andes JTAG Programmer yes (auto)
Versaloon-Link JTAG Programmer yes (auto)
USBProg JTAG Programmer yes (auto)
Raisonance RLink JTAG Programmer yes (auto)
Olimex ARM-JTAG-EW Programmer yes (auto)
CMSIS-DAP Compliant Debugger no

Make sure support for the programmer you are using is enabled, and then type make. Once that finishes, type sudo make install.

Now OpenOCD should be installed and ready to go!

3. Run OpenOCD

Now you can run OpenOCD. For example, if you were using an F4 discovery board, you could so something like this:

sudo openocd -f board/stm32f4discovery.cfg

If it worked, you should see something like:

Info : stm32f4x.cpu: hardware has 6 breakpoints, 4 watchpoints

Which means your programmer is ready to go!

You can then use telnet ip_of_pi 4444 to connect to your OpenOCD session and run OpenOCD commands. You can also connect to it with gdb. The most convenient way is to create a .gdbinit file with something like:

target remote my_pi_ipaddress:3333
file my_firmware.elf
monitor reset halt
load

And then you can type gdb (or in my case arm-none-eabi-gdb), and my_firmware.elf is flashed onto the hardware and is ready for debugging!