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Yosuf Taraki
Yosuf Taraki
Visitor II
January 23, 2018
Question

Question about SDMMC_DLEN register

  • January 23, 2018
  • 1 reply
  • 525 views
Posted on January 23, 2018 at 19:57

We are developing a new product using STM32F767 processor, with a microSD card for storing data.  Page 

1472 of the Reference Manual (RM0410) contains a description of the SDMMC data length register (SDMMC_DLEN).  There is a cryptic note on this page that reads:

For an SDMMC multibyte transfer the value in the data length register must be between 1 and 512.

I am trying to understand the meaning of this sentence.  I have found that we can read up to 262144 bytes per transfer when reading from the SD card.  This corresponds to 512 sectors. I don't understand why we cannot read more than 262144 bytes per transfer, but am wondering if it is related to the note above.  I would appreciate any help on this question.

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    1 reply

    Tesla DeLorean
    Tesla DeLorean
    Guru
    January 24, 2018
    Posted on January 24, 2018 at 09:34

    More likely to relate to maximal DMA transfer length. Reading 256KB at a time should be pretty efficient.

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