Posts: 3
Joined: Thu Oct 13, 2016 12:10 pm

eMMC card for CM3

Thu Jan 18, 2018 4:59 pm

Hi All,

I am working on a project which relies on database and file storage and I am finding that the raw bandwidth between storage card and CPU is a big limitation. I can get around it by using a second SD card connected to a different SDIO interface effectively splitting data between two storage mediums. Primary storage will be used for booting and database and secondary will be used for data storage.

Here is the plan so far.

I plan on using:
uart0 for onboard micro controller communication.
uart1 is reserved for debug.
i2c-0 reserved for camera (I think it is used by video core to detect devices).
i2c-1 for rtc and other stuff.
SPI0 for display.
SPI1 for extra module.
SDx for either emmc or SD card.
SDIO (SD0 gpio 22-27) for wifi.
SDIO (SD1 gpis 34-43) for emmc/sd card.
USB is pretty much taxed and driving external components.

However I am finding it difficult to enable SDIO interface on gpio 34-39. There seems to be no reference anywhere except for CM3 pinout.

Anyone know how to do this?
Last edited by xkam1x on Fri Jan 19, 2018 8:11 pm, edited 1 time in total.

Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2006
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: Additional SD Card on CM3

Thu Jan 18, 2018 5:11 pm

This question has been asked before in various forms - see viewtopic.php?f=98&t=194739.

Posts: 3
Joined: Thu Oct 13, 2016 12:10 pm

Re: Additional SD Card on CM3

Fri Jan 19, 2018 4:01 pm

Thanks for the link but all they are doing is moving the interface around.

Looks like I misunderstood that BCM had SDX_x, SD0 and SD1 interfaces; in reality SD0 and SDX_x are the same thing. This changes things and my new approach is the following.

Use compute module 3 with 4GB emmc flash on SD0 for OS and app.
Attach a 32GB emmc chip on SD1; pins 34 to 43 with x8 link for database and file storage and move the wifi to USB interface.

I would like to know:

What emmc interface is available at BCM SD1? emmc 4.41, 4.5 or 5.0
What is the clock frequency BCM supports? Samsung advertises 200MHz clock.
Has anyone used emmc chip? If so, what model/capacity?


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