Ed Sutter edsutterjr at gmail.com
Sat Jul 18 17:18:59 UTC 2015

>> Meanwhile, I'm just going to let my board soak with the memory test
>> running..
>> "mt -vc 0x80100000 0x1fefffff"
>> Hopefully I'll come back in few hours and it will still be running!
>> Next is MMC right?
> Yes, I am currently looking into MMC right now.  It's a whole
> different world with MMC compared to DDR3.  I hope to get it up and
> running within the week or so which also depends on how fast I am able
> to comprehend the MMC interface specifications.
> For my reference, I am using the following:
> 1. Physical Layer Simplified Specification:
> https://www.sdcard.org/downloads/pls/part1_410.pdf
> 2. SD Host Controller Simplified Specification:
> https://www.sdcard.org/downloads/pls/partA2_300.pdf
> and...
> 3. AM335x TRM, Section 18 "Multimedia Card (MMC)"
> I'll first target accessing an SD card and then the onboard eMMC next.
Take baby steps. No need to implement every detail of the spec, at least not
initially.  Start with just reading id registers and verifying that the card is plugged in.
Then tackle block read and block write.  With that much working, you should be
able to hook your code into the mmc command we talked about and have command
line access to the device.  You basically need four high level functions: read/write/control
just like normal device interfaces at user level.
> >From what I have looked into so far, the interface to both is
> practically similar with some differences on how the AM335x
> initializes the interface and how communications take place between
> them.
I'm no MMC expert, but I think eMMC and uSD are essentially identical (don't test me
on that) regarding the interface.  Both are in the MMC class of devices, so hopefully
once you get one working, the other will just fall into place.
SD cards used to also have an SPI-interface mode, but I think that's fading away.
Anyway, keep up the good work!!
Enjoy the weekend!

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