retrohax.net

… 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

Riiiiighty!
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 I had one already but it was kinda outdated so quick download and install and fixed it.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://git.code.sf.net/p/urjtag/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.

./autogen.sh

make

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

Recovering

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 recovery.beer 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

detect

SUCCESS!

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.

YAY! It’s ALIVE!

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

Greetz

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

OUTRO

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