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How to disconnect the AM335x USB as the device mode from the USB bus

Daisuke Maeda
Guru 20205 points

The AM335x USB operate as the device mode and Full-Speed.

It can simulate a disconnect that the SOFTCONN bit of POWER register (bit 6) is cleared to 0.
Can it disable the 1.5Kohm pull-up resistor on the D+ line automatically?

Best regards,

Daisuke

 

  • 0
    TI__Guru**** 393215 points
    Hi Daisuke,
     
    I have asked the factory team to look into this.
  • 0 in reply to Biser Gatchev-XID
    Guru 20205 points

    Hi Biser,

    Thank you for your reply.

    Our customer wants to know how to disable the internal 1.5Kohm pull-up resistor on the D+ line to notify the external host that the USB device can remove from the USB bus.

    I am waiting for your answer.

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 393215 points
    Hi Daisuke,
     
    Here is the reply from the factory team: Once SOFTCONN is cleared, the host will not see the pullup. It does not matter if the pullup still exists on the device side or not.
  • 0 in reply to Daisuke Maeda
    TI__Guru**** 167581 points

    Daisuke Maeda said:
    Our customer wants to know how to disable the internal 1.5Kohm pull-up resistor on the D+ line to notify the external host that the USB device can remove from the USB bus.

    The D+ or D- pullup only exists in the very beginning of the enumeration process for a very short of the time. After the enumeration is complete, the pullup is disabled for the whole life cycle of the connection.

    I guess in your project, AM335x MUSB in device mode is permanently  connected into the USB host, and you want to disconnect sometimes? If so, clearing SOFTCONN may not be the best solution. Could you please describe the USB requirement in your design? Do you use Linux or other OS?

  • 0 in reply to Bin Liu
    TI__Guru**** 167581 points

    Sorry, please ignore my message above. It was incorrect for full-speed.

    To answer your initial question, yes, clearing SOFTCONN bit will disable the pullup and you can use it to simulate disconnect from the host. Just ensure to teardown the connect state in OTG state machine in your driver after cleared SOFTCONN bit.

  • 0 in reply to Biser Gatchev-XID
    Guru 20205 points

    Hi Biser,

    Thank you for your reply.

    The AM335x as a device side clears SOFTCONN bit.

    Best regards,

    Daisuke

     

  • 0 in reply to Bin Liu
    Guru 20205 points

    Hi Bin Liu,

    Thank you for your reply.

    Is clearing SOFTCONN bit the most suitable procedure initiated by the USB device side to remove the USB device from the USB bus?

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 167581 points

    In most of the use cases, no, clearing SOFTCONN is not suitable for remove the USB device. When unplugged the USB cable, MUSB generates DISCONNECT interrupt, the device driver should handle this event and teardown the driver state for both MUSB and the gadget driver.

    But if AM335x/MUSB is permanently connected to the USB host and there is no USB cable to disconnect, then I think SOFTCONN is a better alternative to remove the USB device. The driver has to do the same handling as that for DISCONNECT interrupt.

  • 0 in reply to Bin Liu
    Guru 20205 points

    Hi Bin Liu,

    Thank you for your reply.

    Best regards,

    Daisuke