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configuring MMC for standard speed vs. high speed mode

burchmere
Intellectual 930 points
Other Parts Discussed in Thread: OMAP3530

The OMAP3530 data sheet () includes different timing specifications for the MMC interfaces depending on whether they are operating in "standard" or "high-speed" mode.  How is the mode controlled via software?  I see no bit(s) in any of the MMC registers that would seem to change the mode.  I understand that a device attached to the MMC interface can support standard or high-speed modes, and that this info is exchanged during part of device "discovery", and that the OMAP MMC controller must explicitly switch the device to high-speed mode from standard mode with a special command.  However, I still don't see how the mode is set on the OMAP MMC itself.

Thanks.

  • 0
    TI__Mastermind 41665 points

    It looks like this is discussed in section 1.6.1.3.4.1.2 (yes, it is really that deep of a section) of chapter 22 of the OMAP35x TRM. It seems you go to high speed mode by modifying the divider value of the card's clock in MMCHS_SYSCTL to be a value of 2 so it operates at 48MHz. I don't think there is a 'high-speed mode' bit, apart from changing the operating frequency of the card itself.

  • 0 in reply to Bernie Thompson TI
    Genius 5470 points

    Yes, this is true. High speed mode just means the card is clocked faster (48Mhz as opposed to ~24Mhz or slower). The max clock speed can be read from the cards profile parameters (which are initially read at a very slow clock rate to support old MMC cards) after reading the controller can bump up the speed if the card supports it.

  • 0 in reply to DavidVescovi
    Intellectual 930 points

    As I understand it, the card reports whether it supports standard mode or high-speed mode, and also reports its max clock speed.  However, changing the clock speed is not sufficient to change the mode.  The MMC CMD6 is required to change mode - then the clock speed can be adjusted appropriately.  The OMAP (and I believe all MMC devices) actually specifies different timing charactersitics depending on the speed mode it's in.

     

  • 0 in reply to burchmere
    Genius 5470 points

    I have used the CMD 6 for changing between 1 bit and 4 bit mode but did not realize it was also used for high speed.