MPX8xx: MMC over SPI....
wd at denx.de
Wed Mar 10 10:59:50 EST 2004
In message <404E51E7.4070909 at iti.fi> 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
> 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 :-)
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at 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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