libblock and FAT

Mozzhuhin Andrey amozzhuhin at
Mon Aug 26 06:19:50 UTC 2013

On 26.08.2013 05:33, Chris Johns wrote:
> Claus, Ric wrote:
>> I've been writing an SDHCI/MMC driver for use with the Xilinx ZYNQ.  
>> Specifically, it is for use with SD cards and I am using 4 GB cards 
>> from Samsung for debugging and testing.  These advertise a read rate 
>> ability of up to 24 MB/s. The average rate that I'm seeing is no 
>> where near that and I've traced the cause down to several points:
>> 1) The ZYNQ's SD/SDIO host controller takes order 650 uS to respond 
>> with DATA_AVAILABLE after being sent a read command. The cause of 
>> this may, of course, be the SD card and not the host controller.  
>> However, the same card can be read and written by a Mac much quicker 
>> than I can achieve with the ZYNQ and RTEMS.
> Read speed and latency are different values. There are also speed 
> settings related to the card that may need to be configured in the 
> driver. By default cards start slow and the driver can speed up the 
> access once the type of card is known.

Also, check that host and card work in 4-wire mode.

Mozzhuhin Andrey

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