[U-Boot-Users] drivers MMCplus for at91sam9x

[Pierre Ossman]

On Thu, 10 Apr 2008 17:31:24 -0500
Ken.Fuchs at bench.com wrote:

> Pierre Savary wrote:
> 
> > I use a MMCplus 4GB on my design (with at91sam9260). It's 
> > wired with 4 bits.
> 
> The MCI controller on the AT91SAM926x family does not support
> MMCplus.  There is no way to support a 4 bit bus, since the
> MCI controller supports only 1 bit to an MMC chip.

Untrue. The hardware interface is identical for 4-bit SD and 4-bit MMC.
So if that part isn't working, it's because you either have a bug or
because you lack 4-bit MMC support entirely in u-boot.

> I know that the MCI controller can be used to access 1GB MMCplus chips,
> but I'm not sure it can be used to access MMCplus chips larger than
> that.
> There may be a special MMCplus command that will allow larger chips to
> be accessed.  Try looking for it in your MMCplus chip's manual.

All compliant cards above 2 GB require special handling. They use a
system identical to SDHC (except for the init). Check the specs (this
part is publicly available) or the Linux code.

On Fri, 11 Apr 2008 10:26:52 +0200
"Pierre Savary" <pierre.savary at kerlink.fr> wrote:

> Thanks a lot for your help.
> In fact it's not really important to support MMCplus, the main is to support
> MMC v4 where the extended CSD is introduced. Moreover, it's not really
> important if only one wire is used... I want only be able to read on a MMC
> 4Gb with my U-boot...

Just to avoid some more confusion, MMCplus is the marketing name of the
full size MMC cards since version 4. So when discussing technical
attributes, the MMCplus/MMCmobile distinction is not that useful.
It's better to just call them v4. :)

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org