Debricking ZX-Uno

… or how to keep on learning new stuff

Background story

A few days ago, I was visiting my friend Bart030. Bart received a bricked ZX-Uno board for repairs. However, he didn’t have a working Raspberry PI unit so he asked me to work on this broken puppy.

ZX-Uno is an awesome project by a Spanish team of guys.

  • McLeod – Reviews and proposes, is a de facto partner.
  • Superfo – Router, which is responsible for designing the PCB.
  • AntonioVillena – Initial idea, scheme design, and prototype distribution.
  • Quest – Ports of secondary cores. Multiboot system. Firmware and prototypes collaboration
  • Hark0 – Graphic and web designer.

They did a great job with this project. Bringing this kind of device nowadays is IMO super cool and I wish those guys the best of luck in future upgrades and projects.

Why I wrote this post?

Well, I was trying to fix this lil machine and after a while of googling, I figured that most of the important information is written in Spanish. I agree that a lot of people speak and understand Spanish but I am not one of them … even after having 0.7L of whiskey, all I can say in Spanish is “Cerveza porfavor” … and I am not even sure if it is correct 😀

The juice

So this little puppy was not booting at all – a blank screen after supplying power to it. The owner of ZX-Uno said that it happened after he tried to upgrade firmware. I started to google stuff and I’ve found a few interesting topics.

So it turns out that it is possible to make a JTAG programmer out of RaspPI!
I completely wasn’t aware of that!
There is a fully working software that does the job – URJTAG
So YEAH, Xilinx chips can be programmed using a simple cable connected to Raspberry PI GPIOs.
According to one of ZX-Uno’s creators, that was enough to recover dead ZX-Uno from the dark abyss. Antonio Villena put a great tutorial online on forums … unfortunately in Spanish. However, that wasn’t much of a problem – google translate FTW!one!eleven111!11!

There are a few ways to recover the bricked device from a “lost” state and I’ll focus on JTAG using RPIs GPIO today.

Preparing RPI OS

A fresh install of Raspbian had to be deployed on my RPI 1 B+. I had one already but it was kinda outdated so quick download and install and fixed it.

Next, I had to download and install urjtag from GIT

sudo apt-get update

sudo apt-get install autoconf autopoint libtool

sudo apt-get install libreadline-dev python-dev git

git clone git:// urjtag-git

cd urjtag-git/urjtag

A file in src/cmd/cmd_bfin.c had to be edited by simply adding a line: #define _SYS_UCONTEXT_H

Everything was ready for compilation.



sudo make install

sudo ldconfig

JTAG cable

Ok, with the software ready and waiting, I could start to prepare the cable. I didn’t have a proper 6-pin connector so I had to solder the cable directly to JTAG pins on Zx-Uno.

Only five out of six wires are needed because I do not need to supply power (3.3V) to the FPGA chip via JTAG, it will be powered by the original Zx-Uno PSU.
Here is a PDF with details

Connecting it to RPI is quite straightforward.
Zx-Uno Raspberry pi JTAG Pin GPIO Pin TMS 6 ------ GPIO6 31 TDI 5 ------ GPIO13 33 TDO 4 ------ GPIO19 35 TCK 3 ------ GPIO26 37 GND 2 ------ GND 39


There are two files needed for recovery.
First, is recovery.bit provided by Antonio and which will be uploaded to FPGA through JTAG straight from Raspberry PI and a second FLASH.ZX1 which has to be uploaded to the root directory of the SD card and plugged into Zx-Uno to reflash its firmware from the BIOS menu.
Everything was connected and ready but it was Saturday evening … aaaaand…

… and I had to leave this project for another day.
Another day came and as usual, I had to recover myself first. Quick was uploaded and right after that, I was ready for recovery.bit upload. I’ve launched urjtag, configured GPIO, and tried to detect the FPGA chip.

sudo jtag

config of GPIOs inside urjtag
cable gpio tdi=13 tdo=19 tck=26 tms=6



So, I could start to load a recovery.bit with the following command inside urjtag.

pld load recovery.bit

Here is how it looked … feat. my new Lamers scarf ;P

Zx-UNO Recovery – Loading recovery.bit through RPI (JTAG) from pit on Vimeo.

After a while, I was greeted with Zx-Uno limited BIOS menu.

With the SD card plugged in I wanted to re-flash software however, I’ve encountered the following FAIL ;P

Zx-UNO Recovery – SD Card FS Fail :> from pit on Vimeo.

It turned out that FAT32 wasn’t cleanly unmounted and a dirty bit was set on it so I moved the SD card to my Linux box and did a quick:

fsck.fat /dev/sdb1

Back to UNO = Mission complete 😉

Zx-UNO Recovery – SD Card burn successful ! from pit on Vimeo.

With new FLASH.ZX1 uploaded for FPGA there was nothing left except testing.

Zx-UNO Recovery – Final test run! Works !!!11oneone!1eleven1 from pit on Vimeo.


Also FYI there is a nice case model for all of you 3D printing fans 😉


  • Zx-Uno team – for awesome project
  • Bart030 – for repair opportunity
  • Owner – for bricking the device 😉
  • Lamers – for an awesome scarf. lol 😀


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5 thoughts on “Debricking ZX-Uno

  1. Thanks for this! I was able to unbrick our 512k ZX Uno using this guide 🙂
    Some notes:

    you have to compile the latest URJTAG from git, the one in APT repo will not work (will not recognize stepping)
    I got error “fatal error: Python.h: No such file or directory” during compilation which was fixed by installing python3-dev
    to flash, I had to use a 128 MB SD card – bigger ones didn’t work (flash progress bar never starts to move) even though a 1 GB card worked happily with ZX Uno when not flashing stuff
    Lacking a proper JTAG cable and not wanting to solder, I resorted to a “crazy” solution of using 5 dupont jumper wires (female-female), where I removed the plastic connector case on ZX Uno side, compressed the “hole” into an oval using pliers and wrapped the end in kapton tape to prevent the pins from shorting. It’s quite a hack, but worked for me 🙂

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