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AM3715 OTG port hot plug problem

Colman Lai
Intellectual 830 points

I have conducted two tests on the USB OTG of 3715 EVM board:

1. After the sysytem boot up, I attached a keypad device to the OTG port, system does not respond to it. The power to the device is off.

2. The keypad device is attached to the OTG port before system boot up. It can recongise the device and the device is working. But if the device is unplugged and then plugged again, system does not respond to it. There is no power to the device.

Can this problem be fixed?

 

Regards,

Colman

 

  • 0
    TI__Guru 63145 points

    A standard USB host/device connection is initiated by connecting a USB device to a USB host.  This is a hot plug event and the USB device signals a connection by pulling one of the data signals high to indicate if it is a low speed or high speed device.  The USB host detects the pull-up and begins to enumerate the USB device.

     

    A USB OTG device connection may not be initiated by cable connection.  USB OTG was developed for connecting two battery powered handheld devices.  A cable is normally connected between the two OTG devices and a user initiates the connection from a menu selection.  The OTG device which initiates the connection will sample its ID pin to determine if it should operate as host.  If its ID pin is connected to ground with less than 10ohms of resistance, it turns on VBUS and begins normal host communications.  If its ID pin is open circuit, it will generate an SRP to get the attached OTG device to begin normal host communications.

     

    The software driver may be checking the ID pin when it powers up, but otherwise waiting for a user request to initiate a connection.  You must send a start session command before it applies power and begins enumeration.  Please refer to the following wiki article and see if this resolves the problem.

     

    Regards,

    Paul  

     

    http://processors.wiki.ti.com/index.php/UserGuideUsbDriver_PSP_03.00.00.05#USB_OTG_.28HNP.2FSRP.29_testing

  • 0 in reply to peaves
    TI__Guru 63145 points

    I forgot to mention the USB OTG port can operate as standard USB host, standard USB peripheral, or USB OTG device.  The mode of operation is determined by the software driver.

     

    Regards,

    Paul