Re: MPX8xx: MMC over SPI....

In message [ref] you wrote:

There is simple spi driver arch/ppc/8260_io/cpm_spi.c but i think that
one like
i2c subsystem will be much more usefull. I have been planning make one based
on i2c driver.

Arghh.... Why do you think you need all this overhead?

I am plannigg 3-layer model like in i2c or USB. interface-HW-driver in
lowest level,
then subsystem driver and then target HW driver. Like in this case
PSC_SPI-> SPI_subsystem->MMC  ---->FS

Remember that SPI is always very board-specific. I'm not sure that it
really makes sense to create a special "SPI subsystem"  -  especially
when you use I2C as a model (which IMHO is just a lot of overkill).

There is same problem in mpc5200 SPI and for this reason i am planning to
use PSC in SPI mode. Then i will have fifo etc. I am also considering to
use bestcom DMA. I just have heard that there is lot of problems with it
when used with I2S. What is actually causing the problems ?

The design of the available (at the moment) bestcomm code.

Bestcom API library ? Should it be better to use directly bestcom HW
without library ?

Do yourself a favour and use the official API. Otherwise you will end
up relying on a lot of internal things that may (and will) be cahnged
with the next version of the bestcomm code.

Of cource it does not give best performance but it is also wery simple
glueless
interface to cheap small low cost mass media. If we like to have full fast
MMC/SD interface then we should consider some FPGA implementation
but in most cases simpler will give enough proformace.

I don't know your exact application,  but  it  always  gives  me  the
creeps when I read the phrases "mass storage device" and "SPI bus" in
the same sentence. I tend to summarize this as follows:
"mass storage device"  + "SPI bus" = need for redesign :-)

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
By the way, ALL software projects are done by iterative  prototyping.
Some companies call their prototypes "releases", that's all.

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