Posts: 1
Joined: Fri May 21, 2021 12:34 pm

CM3+ lowering SDIO clock

Fri May 21, 2021 12:49 pm

Hi Guys,

I am on a custom PCB where the routings between my CM3+ module and a eMMC chip on MMC1 interface (GPIO 34-39) is far from ideal.

We experience random crashes related to the emmc driver.

I am therefore looking into a way of lowering the clock speed on the bus, in the hope of having some of our problems evaporate.

We have identified the boot parameter "sdio_overclock" in config.txt.

Changing this does nothing on the CM3+ module, but it does change clock on the CM3 module. We checked with an osciloscope.

Also when testing the CM3 module against our EMMC chip it does not detect it at all.

Any hints to how I possible to lower the speed on the CM3+ MMC1 interface are very welcome.

Kind regards


Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 3950
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: CM3+ lowering SDIO clock

Fri May 21, 2021 1:28 pm

CM3 and CM3+ are identical in this regard (and virtually everything else). Post your two config.txt files.

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