cleverca22
Posts: 3895
Joined: Sat Aug 18, 2012 2:33 pm

Re: cm4 dead - any recovery options?

Fri Jun 18, 2021 7:39 am

Gavinmc42 wrote:
Fri Jun 18, 2021 7:23 am
How many pins does an eMMC chip use?
8bits of data, power, CMD, Clk and reset?
Could even program a Pico to read that.
if its anything like SD cards, then it can even function in an SPI compatible 1 bit mode, so you can just wire any SPI controller up to it
the only thing the 8bit bus gains you, is the ability to move more data per clock cycle
Gavinmc42 wrote:
Fri Jun 18, 2021 7:23 am
I have used Flashrom on Pi's to program SPI flash, will it do eMMC?
https://www.flashrom.org/Downloads
Does not look like it, yet?
no need to involve flashrom, linux natively supports emmc/sd, and it will always just show up as /dev/mmcblk
Gavinmc42 wrote:
Fri Jun 18, 2021 7:23 am
Hey, eMMC, isn't that like NAND flash, SMI GPIO mode?
1.8V I/O?
Use a modified CM4 with 1.8V I/O on a CM4 I/O board to read the eMMC.
Only need to solder a dozen tiny wires to the removed eMMC.
its likely a raw nand flash chip, and an emmc<->flash controller chip, in the same package
you cant get access to the nand side of things without melting it in acid

but you could just desolder it, and then solder it to an SD adapter board

Image

the black part, fits into a normal uSD socket
the blue part, is an emmc module from another SBC, but you could solder the emmc from a CM4 to it, or find a similar board with the chip missing

Image

https://blog.oshpark.com/2017/02/23/retro-cpc-dongle/

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Gavinmc42
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Re: cm4 dead - any recovery options?

Fri Jun 18, 2021 8:08 am

1 or 4 pin mode still work?

Boot a Pi from USB then use one of those adapters to read it.
Still assuming the EMMC chip is not toasted.

Saw a two uSD card boot adapter, seemed cheap enough.
Hot air gun to desolder, solder wires to adapter.

The datasheet for the Samsung eMMC on my CM4 was available.
Could it be read in circuit without desoldering?

Tracing those tracks would be a pain.
Hmm, under the scope there are plenty of vias.
Not much room to solder and would need the PCB layout design.

Would not want to do this myself.
Time to think about a better backup system.
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drmatt
Posts: 37
Joined: Sat Sep 07, 2019 3:47 am

Re: cm4 dead - any recovery options?

Sun Jun 20, 2021 12:23 am

If you don't have any backup at all this is a lesson learned for you! Clone the uSD/eMMC on.a regular basis when compiling on the RPI or start crosscompiling.
You're right! Fortunately we do builds on a separate development pi and push them, so no code was lost. We also have nightly scheduled backups of data files (though not a full eMMC clone), so most data is ok, but there are some files collected during the day that weren't yet backed up - that's what I was hoping to save.

Thanks to all for the discussion. I think most of the possible solutions are beyond my skill set and available equipment, but among them it seems that the simplest would be to remove the eMMC module and connect it to an adapter as suggested. As was pointed out, we have to weigh the amount of effort vs. the value of the data.

cleverca22
Posts: 3895
Joined: Sat Aug 18, 2012 2:33 pm

Re: cm4 dead - any recovery options?

Sun Jun 20, 2021 2:59 am

If you don't have any backup at all this is a lesson learned for you! Clone the uSD/eMMC on.a regular basis when compiling on the RPI or start crosscompiling.
another option is things like iscsi

a few years back, i was booting a few rpi's with the entire rootfs on iscsi, so i was sharing out a single raid array between many pi's

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