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How to config the MMCHS in High-Speed mode

mu ye
Prodigy 65 points

I am working with am335x.    The writing speed of my SD is only 1.2M/s.  The clock is 24MHz .It does not work when I change the clock to 48MHz

How to improve the speed?  Does the High-Speed mode help?   And how to config it?

  • 0
    TI__Guru**** 393215 points
    Write speed depends also on your SD card speed rating - whether it can accept higher clock rates. Another factor is whether a single large file is being written (faster) or a large number of small files (much slower).
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 63125 points

    Changing the frequency to 48MHz may cause timing violations for AM335x or SD card.

    You may be possible to improve timing by putting the interface into high speed mode.  For more information related to high speed mode, please read section 18.3.12 of the AM335x Technical Reference Manual.  This section describes how setting the HSPE bit high will cause the AM335x output data to the SD card to change on the rising edge of clock rather than the falling edge of clock.

    This may help resolve your issue where it doesn't work at 48MHz, but as Biser mention the actual throughput depends on many other parameters like SD card speed, operating system overhead, etc.

    Regards,
    Paul