i.mx6ull sd boot bus width

[dluberger]

I'm mostly following the EVK reference design, but I noticed in the boot config via gpio, the sd card boot setting is hard-wired for 1-bit bus width, yet off-the-shelf sd cards are 4-bit.  I read somewhere that during boot you *can* use 1-bit communication (i'm not sure why one would do that) but I don't see anywhere how the sd card peripheral then gets "put back" to 4-bit mode.  clearly the EVK works so it's happening somehow, but I'm not seeing where. Is this simply a matter of configuring in the device tree?  where and how is the boot sd card changed from 1-bit to 4-bit after boot?

[igorpadykov]

Hi David

according to sd specification 4 bit bus width operation mode may be selected/deselected
using ACMD6. The default bus width after power up or GO_IDLE(CMD0) is 1 bit bus width.

For linux usage one can look in sect.32.2.3 Devicetree Binding attached Linux Manual.

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------