[LEDE-DEV] Archer c7 corrupted firmware bootloop - tftp aborting - serial not working

[QWeRKUS qwErkus]

Thank you for your reply. JTAG seems even trickier than serial. So far
all my attempts to scan for a valid JTAG chain end up with:

Error: JTAG scan chain interrogation failed: all zeroes

There a just too many variables to check for a newbie like myself, so
I guess I'll go with the spi programmer. Turns out this is another
thing the pi can do (via flashrom) so no need for new hardware. Are
you sure you need to desolder the chip though ? Shouldn't this be
working with a 8 pin SOIC clamp and and external 3.3V power source (I
have an old ATX PSU doing the job) ?

many thanks for your help,

qwerkus

On Sun, Jun 4, 2017 at 1:19 PM, Russell Senior
<russell at personaltelco.net> wrote:
>>>>>> "QWeRKUS" == QWeRKUS qwErkus <qwerkus at gmail.com> writes:
>
> QWeRKUS> Thank you for your replies. Turns out the problem was the
> QWeRKUS> ground connection, and serial nowworks with
> QWeRKUS> pl2303. Unfortunately I mixed up 2 addresses when flashing the
> QWeRKUS> new firmware, and erased from 0x9f000000 on instead of
> QWeRKUS> 0x9f020000. As a result, my boot loader is corrupt. Now I'm
> QWeRKUS> trying some last resort salvage over JTAG, using an rpi with
> QWeRKUS> openocd as JTAG dongle. Assuming I manage to compile openocd
> QWeRKUS> with ath79 support (which currently fails), can I use the
> QWeRKUS> u-boot from pepe2k to restore my uboot ? I yes, how does it
> QWeRKUS> work: just copying the bin to flash from 0x9f000000 onwards ?
>
> Another approach is to write the flash with an external programmer.  You
> might need to desolder the flash chip, if you can't figure out how to
> hold the CPU in reset.  It looks like the c7 has a regular SPI flash
> chip.  It is probably just an 8-pin part, and not too hard to desolder,
> if you need to.  Solder wick is handy for cleaning up the pads after you
> remove it.
>
> I have recently used a bus pirate or a teensy 3.1 with the flashrom
> program to read/write spi flash.  Likely to be Way easier that trying to
> figure out JTAG.  Make *very* sure you have a (or several) complete
> backup of the flash part before writing over it.
>
>
> --
> Russell Senior, President
> russell at personaltelco.net