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[omap4470/4AJ.2.5P2] SD/eMMC overshooting issue

Sean Yu28
Intellectual 520 points

Hi,

     We encountered an overshooting problem on SD /eMMC. This problem is not happened on 4AJ.2.1(Linux Kernel 3.0),but 4AJ.2.5P2. We reference the document swpa221.pdf that can resolve the overshoot on SD,but eMMC not.  We've also checked the register SDMMC1_DRx_SPEEDCTRL that document mentions for resolving the overshooting issue,but the setting of register SDMMC1_DRx_SPEEDCTRL of 4AJ.2.5P2 is the same with 4AJ.2.1.

reg |= (OMAP4_SDMMC1_DR0_SPEEDCTRL_MASK |
            OMAP4_SDMMC1_DR1_SPEEDCTRL_MASK |
            OMAP4_SDMMC1_DR2_SPEEDCTRL_MASK);

Therefore, we guess the work around of overshooting issue is not on this register. We've checked this thread http://e2e.ti.com/support/omap/f/849/t/236945 ,but no response on it. Could TI have any suggestion on this problem?

regards,

Sean

  • 0
    TI__Guru**** 161600 points

    Hi Sean,

    What is the value of OMAP4_SDMMC1_DRx_SPEEDCTRL registers?  In case of overshoot/undershoot you need to change the value of that register to 0.

    Also as stated in the application note (swpa221.pdf), the best approach when dealing with overshoot is to increase the serial resistor value.

    Best Regards,

    Yordan

  • 0 in reply to Yordan Kovachev
    Intellectual 520 points
    Dear Yordan,
    Orginal value is set to 1. Clear to 0 indeed can resolve SD overshoot, but eMMC not. Both of them use the same controller,MMC1. What we are concerned is why overshoot doesn't occur with 4AJ.2.1, but 4AJ.2.5P2 on the same hardware design. Increase the serial resistor just lower the amplitude,the overshoot wave form still exists. Is there any other registers that we can try to configure?

    regards,
    Sean
  • 0 in reply to Sean Yu28
    Intellectual 520 points
    Dear Yordan,

    We re-measured emmc interface and found the overshooting can be affected by the ground length of probe. We tried to use more short ground to measure the signal,the wave fiorm is fine. So this overshooting issue is not caused by software. Thanks.

    regards,
    Sean