Rage and a slightly less messy mess of fucking wires.

Rage and a slightly less messy mess of fucking wires.

by ferris

And this week: even more chromebook shit :)

I tried some more to communicate with the ROM on the board, to no avail. I wasn't sure whether or not it was a connection issue, an isolation issue, or something else, so I went ahead and ordered a batch of 10 of the same ROM chips to test with.

They arrived within a couple days, and after trying the first one, I couldn't communicate with it either. So I went back to the datasheet and one of the wires I had left disconnected could be configured as a RESET line. I didn't think that would be the default option, but I took a chance, tied the line high, and BLAMO, we finally had comm :) A bit of rewiring etc later to clean things up, and I was finally able to successfully and consistently read the manufacturer and device ID's, as well as the chip's 3 status registers.

Next step was to try and hook the rig up to the chip on the board again - but no dice. Still getting all 0xff's back. I suspected it to be an isolation issue at this point (something else on the board being partially powered by the power I was supplying to the chip and interfering with comm, and some quick multimeter measurements supported this) so I did a bit of digging.

I ended up finding this guide for in-system programming using the flashrom utility, where it's mentioned that you could try to power the chip normally from the board, and communicate with it anyways. It also recommends trying to power the board but hold it in reset; I wasn't able to find any reset button/pins/wtf on this particular board so I just went for it and hooked everything up anyways.

Unfortunately, still no comm. Measurements of the pins indicate that everything I'm supplying to them should be safe and correct, but something seems to pull the comm lines low on the board anyways and there doesn't seem to be a way around that.

At this point it would seem the only option left is to actually desolder the chip from the board, which, naturally, scares the shit out of me. However, I've read elsewhere it's possible to actually file down the pins of a chip like this to remove it first (given you don't mind trashing the chip), at which point it's supposedly fairly easy to clean the rest up and solder something new on there. If possible, I might try to replace the chip with a socket instead, at least on one of the chromebooks. But I'll have to think about it more; I run the risk of really ruining something at that point, and the modification might be irreversible. But ideally, if I could get a socket in there, I would be able to iterate properly on building a linux-supporting boot ROM, at which point I could potentially solder a pre-programmed chip (since I have so many haha) back onto the board, and voila, fixed. Potentially. :)

In any case, I took some time to make sure I actually could get by backup bios onto the test chips with the flashrom utility. And, as it says on the tin - it's quite easy. It's almost as if they made that tool specifically for this purpose! :P So yeah, gonna start shopping for sockets I suppose.

Until next time!

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Last Edited on Sun Feb 21 2016 22:37:24 GMT-0500 (EST)