[coreboot] How to repair Pomona clips, Was: Good source for SOIC clips

[Denis 'GNUtoo' Carikli]

On Sat, 19 Mar 2016 20:19:00 +0100
thomasg <thomas at gstaedtner.net> wrote:

> These are certainly much cheaper than the expensive ones available in
> the "west" - though I don't know if the quality is adequate.
> Should you order some it would probably be interesting to give
> feedback on that.
I've a SOIC-8 Pomona clip. I used it very extensively when I was
working on replacing the VGA option ROM for the Lenovo X60.

The Pomona clip I have is composed of plastic and long metallic pins.

After my extensive use, the metallic pins are now bent, that prevents
them from reaching the SOIC-8 chip.

You can easily detect that when trying to connect the Pomona clip: the
clip tend not to stay in place anymore, and you have a very hard time
preventing it from being disconnected from the chip.

My solution was, to disassemble the clip, that means removing
the metal part in the middle that keeps everything together.

Then inside, at some point, pins are bent at 90 degrees (that's
normal) but they didn't stick to the plastic.

Good state:
-----------

Connection          +----------------- SOIC-8 chip pin
to the external     |
flasher ------------+

Bad state:
----------
Connection          +--------------- SOIC-8 chip pin
to the external    /
flasher ----------+


So here just pushing the pin from the "Connection to the external
flasher" side, near the 90 degree bending, with a needle or a
screwdriver did the trick.

Then at some point it bends again, so you repair it again and so on.

After a while the pins, on the SOIC-8 side start detaching themselves
from the plastic. So I glued them.

I can still use my clip, even if it's way harder to use it right than
before, positioning it is harder, and you might need to keep it in
place with one hand, while typing the flashing commands with the other
hand.

Solution:
---------
You probably don't need to externally reflash that often:
Assuming you work on code that makes your board not boot, just use the
normal/fallback mechanism.
Since it's not human-error proof, you still need an external flasher in
case something goes wrong.

Also an external flasher is very useful if you have no other way to
reflash coreboot/libreboot when running the stock BIOS.

It is also mandatory if you want to make sure that the image you
intended to flash was really flashed unmodified on the flash chip.

SMM/SMI and various southbridges makes it way too easy to implement
rootkits that modifies what is read or written from the flash, on the
fly: such southbridge can be programmed to emit an SMI interrupt when
the flash is accessed. Then whatever code that is running in SMM, can
potentially modify what is being read or flashed, before the CPU
returns to its previous context.

Denis.
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