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SD card reader write/read single block

Posted on January 15, 2014 at 11:48

We checked some SDHC Card Readers and we noticed that they are using the Multiple Block Write CMD25 for writing a single sector and Multiple Block Read CMD18 for reading a sincle sector. The SDIO protocol has Single Block commands CMD24 and CMD 17 for writing or reading a single sector.

Does anyone know why the Card Readers are not using the single block commands for treating a single sector?

Associate II
Posted on January 15, 2014 at 13:44

The SD card specifications recommend to use ReadMultiBlocks and WriteMultiBlocks  over ReadBlock and WriteBlock, I don't remember why specifically but based on my own experience with STM and SDIO is so much faster and efficient.

Posted on January 15, 2014 at 14:26

The command processing overhead is quite significant, streaming sequential reads/write are both far more efficient, and predictable (and thus optimized for and pipelined).

Practically all storage media works better with large collections of sectors handle at once, ie a whole cluster. Writing single blocks, or partial blocks, being by far the least efficient.
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Posted on January 15, 2014 at 18:36

Thanks, it make sense.