[U-Boot-Users] drivers MMCplus for at91sam9x

[Pierre Ossman]

On Fri, 11 Apr 2008 13:54:13 -0500
Ken.Fuchs at bench.com wrote:

> 
> The manual for the AT91SAM926x processors clearly states that the
> MCI controller supports MMC 2.2.  I asked Atmel whether this controller
> could support 4 bits to an MMC 4.x chip and they said _no_.   The answer
> is supposedly from their engineering group in France.
> 

What they answered was if Atmel would support such a solution, not if
the hardware would.

> 
> How does one program the MCI controller to send 4 bit (parallel) data
> an MMC 4.x chip, with or without telling it that it is communicating
> to a 4-bit SD chip?  The only way to get 4 bits of data out of the MCI
> is to tell it that it is connected to a SD (1.0) chip.  If you program
> the MCI to communicate with an MMC chip, it will send data out only on
> the low order bit.

You tell it to use all four bits. That's it. The setting isn't MMC/SD,
it's 1-bit/4-bit.

> Both ends of the communication link must considered.  It may not be
> sufficient that the MMC chip is MMC 4.x; The fact that the MCI
> controller is only MMC 2.2 or SD 1.0 compliant, may or may not impact
> this special handling.

It does not in the slightest. Remember that these controllers are
extremely dumb. The low level behaviour of the protocol hasn't changed
since the very first specs, so only software needs to be changed to
support even the newest features.

Rgds
-- 
     -- Pierre Ossman

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