Enabling MMC2 for 4 bit SDIO Wifi Card

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1

Hi Ya’ll,

I am trying to interface a LSR TIWi-BLE wifi card with my Beaglebone Black. I would like to keep the on board eMMC functional so I cannot use MMC1.

Looking at the Sitara datasheet and the Beaglebone black schematic it seems that all 6 wires needed for 4 bit SDIO SDIO are available on the header.

MMC2_CLK → 8.18
MMC2_CMD → 9.15 (also attached to another input, would need to remove R160?)
MMC2_DAT0 → 8.12
MMC2_DAT1 → 8.11
MMC2_DAT2 → 8.16
MMC2_DAT3 → 8.15

Do I just need to write an overlay to enable these pins for mmc function in the cape manager?

I’m currently waiting for the device to begin testing, but I am surprised to see that I could not find any resources or documentation of someone interfacing with a 4 bit SDIO device on MMC2 while maintaining eMMC func on MMC1

Would love to hear if anyone has accomplished this already and how they went about solving this problem.

Cheers,
Danny Salzman

2

the mmc layer in v4.1.x wasn't happy as an overlay, take a look at the
wl1835mod cape/board example:

https://github.com/beagleboard/linux/blob/4.1/arch/arm/boot/dts/am335x-boneblack-wl1835mod.dts
https://github.com/beagleboard/linux/blob/4.1/arch/arm/boot/dts/am335x-boneblack-wl1835mod-cape.dtsi

Regards,

3

Looking at those files I see that the wl1835 utilizes the MMC1 pins. I want to try and keep the MMC1 for the eMMC and only use the MMC2.

Does the Beaglebone Black support this from a HW point of view? I have not found any example of someone using the MMC2 bus.

Cheers,
Danny

P.S. Thank you Robert for all your effort and time you put into the Beaglebone project!

4

The pins are on the expansion connector. The determination as to how they work and if it is adequate for whatever purpose is dictated by the processor itself and the SW support.

I do not know of anyone hat has used these pins for SDIO. But per the documentation from TI, they should be able to do it.

Gerald

5

Hey Danny,

How did you go with this?

I am looking at doing the exact same thing, any results yet?

Cheers

NP

6

Hi Nick,

Do to lack of resources we have backlogged this for now.

It seems possible, but I have still not found any working example.

-Danny

7

Just last month I wrote a brief blog about interfacing a second sd card to the mmc2 lines of the beaglebone black : https://2captiv8.blogspot.com/2016/07/interfacing-second-sd-card-reader-to.html . Hopefully you can use it as a guide for future purposes.

8

Fantastic, thanks for the update