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meir
meir
Associate
January 15, 2014
Question

SD card reader write/read single block

  • January 15, 2014
  • 3 replies
  • 1645 views
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?

#sdio-cmd24-cmd17
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3 replies

dmg0048
dmg0048
Associate III
January 15, 2014
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.

Tesla DeLorean
Tesla DeLorean
Guru
January 15, 2014
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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meir
meirAuthor
Associate
January 15, 2014
Posted on January 15, 2014 at 18:36

Thanks, it make sense.

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