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eMMC Reset Line on am335x

Patrick Luell
Prodigy 20 points

We are designing a board based off the beaglebone black.  We will be using the eMMC.

We noticed that the eMMC has a line connected for eMMC_RSTn; this is connected to ball R14 (GPIO1_20) with an inverter.  On our board the R14 ball is assigned to something else already, so we would need to move this.

It looks like there is nothing in U-Boot that uses the GPIO1_20 pin specifically; however, it looks like Angstrom Linux added support to the 3.8.13 kernel to use this feature.  In the most recent vanilla kernel (3.16.1) it looks like there is no support for the reset feature.  So far I have been able to run the latest kernel on the beaglebone black without any issues.

1) Is the reset line on the eMMC something that should be implemented in linux?

2) Is the reset line only hooked up on the beaglebone black to provide the possibility of this feature without it being required?

3) If the line is required, is it able to be moved to a different pin on the AM335x? And can it be hooked up without the inverter?

Thanks

  • 0
    TI__Guru**** 393215 points

    Hi Patrick,

    Patrick Luell said:
    1) Is the reset line on the eMMC something that should be implemented in linux?

    Not necessarily. This signal is used for hardware reset to the eMMC.

    Patrick Luell said:
    2) Is the reset line only hooked up on the beaglebone black to provide the possibility of this feature without it being required?

    I'm not a software expert. You have to check the Linux sources to see if it's being used.

    Patrick Luell said:
    3) If the line is required, is it able to be moved to a different pin on the AM335x? And can it be hooked up without the inverter?

    Yes, you can move it to any available GPIO output. The inverter may be needed if your chosen GPIO defaults to a low state when the processor is in reset, or at reset release. This will hold the eMMC in reset, preventing the processor to boot from it, therefore the need for the inverter.

  • 0 in reply to Biser Gatchev-XID
    Prodigy 20 points

    Thank you for the reply.


    We were able to move the emmc reset line to ball V6, which defaults to HI-Z with active pullup, so we don't need the inverter.


    It does seem like the reset line is not a required feature to implement.  This page, http://elinux.org/Beagleboard:BeagleBoneBlack#Onboard_eMMC , seems to indicate that the reset is available on the beaglebone black to allow the emmc lines to be used by the headers.