Booting from SD on alternate functions

[danielbujak]

I'm attempting to bring up a custom board for the iMX6ul based on the EVK and it seems like the SD card lines are not the same as the EVK. I'm wondering if it is possible to change which pins the boot uSD card is connected to. For example, could we use the alternate functions for one of the GPIOs as the Data line or is the pin-muxing fixed in the boot ROM?

[Carlos_Musich]

Hi danielbujak,

you can just stop in U-boot and edit mmcroot variable to match the sd number you want to use.

Best regards,
Carlos

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[danielbujak]

Hi Carlos,

I'm actually stuck before that as I am unable to load u-boot at all.

The pinout for the SD card on the custom board vs the EVK is as follows:

Signal	EVK pin	Custom Board pin
SD2_nRST	B4	--
SD2_CLK	D8	D8
SD2_CMD	C8	C8
SD2_DATA0	D7	D7
SD2_DATA1	B7	E3
SD2_DATA2	A7	A7
SD2_DATA3	D6	D6

Regards,

Daniel

[Carlos_Musich]

Please check following post.

U-Boot Migration Example 

Best regards,
Carlos

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[danielbujak]

Hi Carlos,

It seems like all this assumes that the device is able to locate the SD card. However, I'm not understanding how the device knows where the SD card is to find uBoot in the first place.

Regards,

Daniel

[Carlos_Musich]

Hi Daniel,

The Boot ROM uses the state of BOOT_MODE and eFUSEs to determine the boot device. For development purposes, eFUSEs used to determine the boot device may be overridden by using GPIO pin inputs.

You can find this information in chapter 8 of Reference Manual.

http://www.nxp.com/docs/en/reference-manual/IMX6ULRM.pdf 

Best regards,
Carlos

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