JTAG de-brick-ing info

[Eric Herman]

Hello firmware hackers,

Looking at the GnuBee schematics[1] I see that U1215 is labeled as a MX25L6406EM2I/NI and the data sheet is available on-line[2]. Looking at the images in the "GnuBee_Docs/DeBrick" directory[3] gives me some hope that someone out there has tried using the JTAG features.

As I have only limited experience with JTAG (only some debugging, not yet for programming/debricking), I am feeling like I am "in a bit over my head" -- I would be much more comfortable trying to update U-Boot if I could find some more information on how to use JTAG on the GnuBee.

Have you used JTAG on the GnuBee? Were you successful? If so, would you be willing to write a bit about your experience? What is your setup? What steps do you take?

Cheers,
 -Eric

[1] https://github.com/gnubee-git/GnuBee_Docs/blob/master/GB-PCx/Documents/GB-PC2_V1.1_schematic.pdf
[2] http://www.macronix.com/Lists/Datasheet/Attachments/6681/MX25L6406E,%203V,%2064Mb,%20v1.9.pdf
[3] https://github.com/gnubee-git/GnuBee_Docs/blob/master/DeBrick/debrick-02.png

[Larry Pinney]

Hi Eric :

The 'full' JTAG isn't available on this device.

Some debricking options :

This method was used for 'R&D'

 

Install a SOP8 socket and install the SPI flash chip on a cheap adapter. (or use an expensive programmer adapter)

https://github.com/gnubee-git/GnuBee_Docs/blob/master/DeBrick/debrick-01.png

###

How to fix a bricked VoCore2 with another VoCore2 :

http://vonger.cn/?p=8054

This type of debrick should also work for the PC1/PC2.

In theory one should be able to use most any Mediatek/Ralink 'MIPS' devices as the 'working device' assuming you have access to the SPI

###

ch341a programmer : I normally use flashrom however flashrom was limited to 16M last time I checked. 

Yes ... one can use a smaller SPI flash chip ... the early units used 16M (if you intend to only run Debian this shouldn't be a problem)

Larry

[Eric Herman]

Hello Larry,

Perhaps a future version will have 'full' JTAG, I'm happy to see that there are at least three de-bricking options available.

The "fix a bricked VoCore2 with another VoCore2" approach looks especially interesting, and I see a variety of ch341a programmers are available for about 10 euro.

Thank you for the information, and the very prompt reply!

Cheers,
 -Eric