Max seep of the SD slot?

Cédric Berger cedric.berger74 at
Fri Jul 25 12:00:42 CEST 2008

On Thu, Jul 24, 2008 at 08:49, Andy Green <andy at> wrote:
> Well, a good rule of thumb for generic 1-bit transfer is divide by 10
> for the max speed in Bytes/sec you could expect, here we have 4-bit so
> the peak raw trasfer speed is ~10MBytes/sec *BUT* after Glamo pulls the
> data from the card, we have to sit there dragging it into the CPU
> memory, on top of card latencies and command setup the speed is way
> slower, still a decent ~2MBytes/sec each way IIRC.
> - -Andy


This is something I also wanted to know for the choice of a new card.

So we may say that up to 10MBytes/s, max speed of the microSD matters.
After it should not much. (?)
(and looks like 10Mbytes/s is currently what offer rather high end microSD)

One more question though : if the card is slow, throughput will be
lower, but will the CPU / glamo graphic bus be able to benefit of more
resources while the card transfer occur ?
Or does it just had to time to wait and CPU / glamo bus are as much
busy (or waiting) ?

Same question if we lower the SD clock rate. Is it equivalent to
having a slower card ?

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