slow MMC over SPI

[Andre Schwarz <andre.schwarz@matrix-vision.de>]

All,

has anybody made some investigations about performance of a SD/MMC card
on SPI ?

Actually I'm using various cards (different speed classes) on an SPI bus
of a MPC8343 cpu.
Everything is working fine basically, i.e. card is detected properly and
block device can be mounted and used.

SPI clock is adjusted to the card's capabilities and is running quite
fast (>30MHz).

But between consecutive reads/writes there's a fixed gap of 2us thus
yielding a poor performance of approx. 300KBytes/sec.
The spi bus is utilized only ~10%.

Any ideas where this comes from ?
Ist it a fixed delay regarding to some kind of spec or is it possibly a
spi driver/mmc layer issue ?


regards,
Andre Schwarz

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