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TUSB2036: Is it possible to start USB communication without reset TUSB2036?

Guru 29690 points
Part Number: TUSB2036

Hi Team,

My customer designed their board with TUSB2036.

USB Host (Android) --- TUSB2036
                                           |      L--- Audio IC *sometimes goes to suspend state
                                           L--- MCU *always communicates with USB Host

1)
If the audio IC goes to suspend state, there is a delay before the audio IC disappears from the USB Host.
The delay is about 5 seconds ~ dozens of seconds.
My customer wants to shorten the delay time to about 1 second. Is it possible?

2)
If the audio IC resumes from suspend state, the audio IC still disappears from the USB Host.
TUSB2036 should be reset to resume USB communication between the USB host and the audio IC in this case.
Is it possible to start communication immediately without reset TUSB2036?

Best Regards,
Yaita

  • Hello Yaita,

    1.  If the audio IC is suspended, it should not disappear from the host.  It should remain connected with DP pulled high.  Is that happening?

    2. How is the audio IC resumed?  It sounds like it is disconnecting and reconnecting.  This is not caused by the TUSB2036, we need to know the audio IC behavior.

    Regards,

    JMMN

  • Hi JMMN,

    Thank you for your reply. I put my comments as follows.

    1.  If the audio IC is suspended, it should not disappear from the host.  It should remain connected with DP pulled high.  Is that happening?
    [Yaita]
    I apologize my explanation wasn't clear. If the audio IC is suspended, it goes "unknown device" on the host.
    It takes 5 seconds ~ dozens of seconds to transition to the "unknown device" state, so my customer wants to shorten the delay time to about 1 second.
    Note) He also confirmed the delay time is about ~1 second if he tested with another commercially available USB hub. 

    2. How is the audio IC resumed?  It sounds like it is disconnecting and reconnecting.  This is not caused by the TUSB2036, we need to know the audio IC behavior.
    [Yaita]
    The audio IC goes to suspend state if an external microphone is unplugged and resumes if it is plugged in.
    The issue is the audio IC is still "unknown device" on the host although the audio IC resumes from suspend state (an external microphone is plugged in). 
    Note) He also confirmed the audio IC pops up on the host normally if he tested with another commercially available USB hub. 

    Best Regards,
    Yaita

  • Hi Yaita,

    1. When a device is suspended it should not transition to "unknown device" on the host.  This is not expected USB behavior so I am not sure what the device is doing or why the status is not getting reported to the host.  It could be that the hub status is not getting polled from the system frequently or that the hub port status is not updated immediately.

    2. Again, this type of reconnect is not typical USB behavior so I cannot identify a way to force the hub to report status faster.

    Unfortunately, there is no way to force the hub to report status faster or more persistently, since this is a state machine based design.  Can the customer provide any USB system logs to hep identify the issue?

    Regards,

    JMMN

  • Hi JMMN-san,

    I apologize for the late reply.

    >1. When a device is suspended it should not transition to "unknown device" on the host.  
    Could you let me know what is expected behavior in this case when the downstream device is suspended?
    It would be appreciated if you advise it.

    Best Regards,
    Yaita

  • How is the downstream device being suspended?  And how is the device status being viewed?  The host should still see the device as connected even though it is suspended.

    Regards,

    JMMN