MPX8xx: MMC over SPI....
wd at denx.de
Wed Mar 10 02:25:10 EST 2004
in message <200403091418.22891.david.jander at protonic.nl> you wrote:
> I know that Wolfgang Denk is going to flame me right away for this, but I'll
> do it anyway :-)
I'm sorry if I caused the impression I would flame people for using
SPI. This was definitely not my intention. But I think it is only
fair to share some experience, and warn you not to run into well-
> I am going to write a SPI driver and on top of that a MMC driver for linux for
> the MPC852T, unless there is something already out there.
> Anyone tried this before and has some sources to share? Or pointers to
The SPI driver is there, but I don't recommend to use it for any type
of data transfers that require any significant bandwidth. Motorola
The SPI was not designed to be a high-bandwidth channel. It
can run very quickly for bursts of up to 16-bits. But the
peripheral has no FIFO and low priority in the MPC860 and
thus you cannot burst lots of data quickly through the
Note that the SPI is of lower priority internally than the
SCCs, thus, the SPI will be the first device to be "starved".
Since it has no FIFO, it is especially sensitive to underruns.
The best way to prevent this is to use a buffer size of 1
"character" (of size programmed in the mode register).
Also, you should be aware that the SPI protocol is implemented as
microcode running on the CPM, so any high-speed data transfers will
suck up CPM performance.
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
"...and the fully armed nuclear warheads, are, of course, merely a
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