[flashrom] Getting inconsistent reads with a Raspberry Pi

[David Hobach]

For reference:

Apparently the Pi didn't provide enough current to drive the chip and 
whatever else hang in the motherboard together with it.

So how I got it done:

1. remove the AC adapter & all batteries incl. CMOS from the laptop

2. attach Pomona clip incl 5 wires for CS -> CE0, SO -> MISO, SI -> 
MOSI, SCLK -> SCLK, GND -> GND (do NOT connect Vcc, HOLD and WP seem 
optional as the motherboard appears to drive them to 3V3)

3. attach the AC adapter & wait for the laptop to boot (if it doesn't, 
try it with the keyboard attached)

4. laptop states that there's a md5sum error with the CMOS (the CMOS 
battery is removed after all)

5. measure CS on the chip - if it's constant 3V3 apparently no one else 
is driving the chip (might make more sense to do that in a first run 
without wires attached)

6. power up the Pi and read multiple times, compare the images afterwards

7. power down the pi, then the laptop

I didn't test writing.

Maybe that'll help someone with the same issue.

KR
David

On 07/13/2017 11:24 PM, David Hobach wrote:
> Dear all,
>
> I'm trying to read a MX25L3206E and a MX25L6406E in-circuit (laptop)
> with a Raspberry Pi Rev.1 using a POMONA 5220 SOIC clip.
> flashrom v0.9.9-r1955 on Linux 4.9.35+ (armv6l)
>
> Unfortunately I keep getting images with varying md5sums.
>
> Moreover, when switching between the chips, flashrom always detects the
> chip it was last connected to (i.e. not the real one) and the MX25L6406E
> is not correctly detected at all in general (incorrectly detected as
> some other chip).
>
> If anyone knows those symptoms, I'd love to hear a comment!
>
> All external power sources are disconnected (incl. CMOS battery). The
> 3v3 of the Pi is used for powering. All 8 Pins were connected (incl.
> Hold and WP to 3v3).
>
> What I checked so far:
> - The factory images on the chips work.
> - SPI loopback on the Pi works (MISO <--> MOSI).
> - Cables are relatively short (tried 28cm and 2* that with a 10k Pullup
> on MISO - the latter didn't seem to change much, but I'm not 100% sure
> yet).
> - Reducing the clock speed didn't seem to make a difference (e.g.
> flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=1000 -r flash03.bin -c
> "MX25L3206E/MX25L3208E").
>
> I didn't try yet:
> - external 3v3 PSU
> - laptop power (I actually connected the AC adapter once without
> booting, but it didn't seem to power the chip - I didn't measure 3v3)
> - putting a 22pF capacitor somewhere (I'm not sure where exactly?)
> - unsolder the chip - I'm trying to avoid that as I'm not good at that...
>
> Do you have any other ideas? Maybe I'm missing something obvious?
>
> I haven't done this for a few years, so any help would be greatly
> appreciated.
>
> Thanks & Kind Regards
> David
>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 2422 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://mail.coreboot.org/pipermail/flashrom/attachments/20170714/f2f02673/attachment.p7s>