Subject: Re: slow MMC over SPI

From: Fabio Tosetto <[email-masked]>
Date: Tue, 03 Jun 2008 07:54:30 +0200

Hello,

I am trying to enable the SD over SPI on a emebedded system with one
processor powerpc mpc5200b; you have enabled mmc over spi into a native 
spi or psc spi?

regards,
Fabio

Andre Schwarz ha scritto:
> 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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