[flashrom] In situ Thinkpad E420 Sandy Bridge/Cougar Point PCH

awokd awokd at danwin1210.me
Sat Mar 24 22:30:25 CET 2018

On Sat, March 24, 2018 7:58 pm, Nico Huber wrote:
> On 24.03.2018 13:49, awokd via flashrom wrote:

> I haven't fully followed the power rails in the schematics. Though,
> what you witnessed sounds much like you also power the PCH and maybe the EC
> too. The overall board layout regarding the SPI flash looks astonishing. I
> wonder why it works at all ;)

"Astonishing" is not very promising sounding. :)

> You might already know the `laptop=force_I_want_a_brick` option for
> internal flashing. This option was introduced because of severe trouble
> with *less* complex situations. It looks like Wistron already placed two
> masters on the SPI bus (it should only be one) and your programmer is the
> third.

I missed that completely.

> If I understand things correctly, the flash chip is shared as much as
> possible (understandable for such a cheap machine).

I'm prepared to sacrifice this machine on the altar of knowledge, although
I am going to miss the nice keyboard.

> 1. the EC stores its
> firmware in it. 2. the ME loads some of its firmware directly over SPI. 3.
> the BIOS is loaded over LPC through the EC (that's the I_want_ a_brick
> scenario). My vague guess is that it only works because the EC can somehow
> predict when the ME is going to access the SPI flash (e.g. within some ms
> after enabling certain power rails).
> I see three solutions here:
> 1. Desolder the flash chip completely. If you just want to flash once,
> solder it back afterwards. Otherwise, add some isolation circuit.
> 2. Replace R6010 and R6011 with diodes. Make sure to remove all bat-
> teries and AC, and power the flash chip directly during programming.
> 3. Cut the VCC pin of the flash chip, solder it together again later
(I've heard
> people are doing that).
> My personal choice would be 2., I would never try 3. (chances are too
> high that you hurt the pad below the VCC pin).

Was hoping to avoid soldering (anything finer than 12 gauge makes me
nervous) but sounds like no choice. I don't follow how
desoldering/soldering 8 or 2 legs is safer than 1 but I'm sure there's
something on Youtube explaining. Maybe it's easier than I think and I just
need to practice. If I can't get it, you might see my own contribution of
a special method of removing ME by judicious application of 220V AC.

Thanks for taking a look!

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