[En-Nut-Discussion] Nut 3: SD/MMC speed?

[Jesper Hansen]

Note that the 20 MHz is a transfer clock.
Most standard SD/MMC cards have a spec'ed block write time of typ 20mS 
to max 250 mS!
If the 133X card really IS 133 times faster at write access, then it 
looks a bit brighter.

CF cards are usually a lot faster.

/Jesper

Aaron Burt wrote:
> Howdy.
> I'm developing a very fast data-recorder.  Ultimately, I hope I can
> write 20MB /sec to a 133x CF or SD card, but for now, I'll settle
> for what I can get.
> 
> Assuming the card is fast enough, how fast can the ethernut write to the
> MMC port?  For some perspective, MMC supports a 20 MHz clock, which
> means ~2.4 MB/s, and SD supports a 25 MHz clock and 4 bits, giving
> ~10MB/s.
> 
> Can the CPLD get those kinds of clock rates?  It looks like I could
> use a state machine to handle the interface and just feed it data from
> the CPU or the expansion port.
> 
> Also, if I'm reprogramming the expansion port, is the CPLD used for
> anything other than SD/MMC and some interconnects?
> 
> Thank you for your time,
>   Aaron Burt
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