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AM3354: eMMC reset signal

user4973896
Expert 1555 points
Part Number: AM3354
Other Parts Discussed in Thread: TIDA-010032

The official website TIDA-010032 is designed to boot  from MMC1, but the reset of MMC1 is controlled by  GPIO. After power-on, CPU has not loaded the program . How to output reset signal from it to reset EMMC and load the program from EMMC. Is this not contradictory? ? WHY?

  • 0
    TI__Guru**** 393215 points

    On eMMC memories the reset signal is NOT enabled by default, therefore there is no need to reset the eMMC by GPIO at boot time. You will find details about the reset signal in the eMMC datasheet.

  • 0 in reply to Biser Gatchev-XID
    Expert 1555 points

    Very  thanks！

  • 0 in reply to user4973896
    TI__Guru*** 125430 points

    I want to add a couple comments:

    1.  In the BeagleBone Black, we had a situation where the MMC peripheral was connected to eMMC and it was also routed to the header.  If for example you were going to use a WiFi cape (SDIO), the software on the processor had to hold the eMMC in reset to prevent contention on the SDIO bus.  I believe that is the original reason for connecting GPIO to the eMMC reset.

    2. For a "normal" design where the MMC peripheral connects only to eMMC, I generally recommend using the nRESETIN_OUT signal for resetting the eMMC.  That way, if the processor resets for any reason (software reset, watchdog, etc.), the eMMC will be forced to a good state.  Note however that nRESETIN_OUT is not a push pull signal.  It is (pseudo) open drain.  You might want to put a logic gate there to convert the reset signal to push-pull before routing to the eMMC.  And as Biser mentioned, there's a one-time programmable bit that you need to write in order to enable the reset pin on the eMMC itself.