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Pi CM3 eMMC bus width, SD1 boot?

Posted: Thu Apr 27, 2017 9:36 pm
by David Wood
Hi All,

What is the bus width of the on board eMMC? Is it able to boot with the 8-bit width the on-chip controller is capable of?

Is it possible to boot from SD1 at an eight bit width, since those pins are available on the CM3?

Thanks in advance for any info you may have.

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Fri Apr 28, 2017 8:47 am
by PhilE
The eMMC is wired to GPIOs 48-53 - only SD0-SD3 are connected.

If you can connect a device to GPIOs 34-43 you might be able to persuade it to work, but as far as I know it is completely untested.

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Wed Jun 28, 2017 6:51 pm
by inches
Can you boot from an SD card using SD1 pins 34-39 in the first place?

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Thu Jun 29, 2017 8:59 am
by gsh
It would be possible to boot from those pins, although currently there is no config.txt parameter to set that option.

Add to firmware issues in github as a request and I'll see about adding it... Unfortunately you cannot disable the boot from pins 48-53 so it'll have to fail there first which will add of the order of 4 seconds to the boot time.

Either that or use the GPIO bootmode options to select this as the bootmode. This also requires some extra code and testing to implement (also on my list)

Gordon

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Sat Jul 29, 2017 12:16 pm
by alberto2033
Hi,

I'm working with a custom board which was intended to be used with the CM3 (not the lite version). Due to low stock I've bought some Lite instead (and back ordered the CM3, but will take ~3 weeks to arrive).

I have an SD, for external storage, connected to pins GPIO34-39. I don't care about the extra 4 s boot as for now I'm just developing and it's only a quick fix while I wait for the CM3 to turn up.

Has any work been done in this direction? Otherwise, could I modify the boot code sent through the USB to configure this interface instead of the eMMC to boot the system?

Thank you and best regards,

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Sat Jul 29, 2017 12:29 pm
by gsh
Unfortunately I've not had time yet to look into it (and a github issue still doesn't exist for it!)

Re: Pi CM3 eMMC bus width, SD1 boot?

Posted: Sun Jul 30, 2017 10:35 am
by alberto2033
I've just created the issue on Github.

I'm going to clone the repository and see if I can find a way.