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How to change AM1808 USB OTG role?

Colman Lai
Intellectual 830 points
Other Parts Discussed in Thread: AM1808, AM3517

When I configure AM1808's USB OTG port as host only, it can detect devices attached. But when I configure it as both host and peripheral port (OTG mode), after boot up, it defaults as USB peripheral. When a A-plug is inserted (ID pin is grounded), the kernel driver change the state to OTG_STATE_A_IDLE, then nothing happen. It does not initiate a session. I am using the kernel source linux-2.6.37-psp03.21.00.04.sdk.tar.gz.

I want to ask how to change the OTG role from peripheral to host and vice versa.

Regards,

Colman

  • 0
    TI__Genius 9460 points

    when in host and device mode (OTG mode) then use "echo F > /proc/driver/musb_hdrc.0" command to switch on the Vbus so that devices gets detected.

    Ajay

  • 0
    Guru 26430 points

    Did you try the TI Wiki? Adding to Ajay's suggestion, here's some links:

    The SW instructions in these links should apply to any newer Linux USB driver.
    http://processors.wiki.ti.com/index.php/UsbgeneralpageLinux-v3p1
    http://processors.wiki.ti.com/index.php/Usbgeneralpage
    http://processors.wiki.ti.com/index.php/Sitara_SDK_5.03.02_Release_Notes
    http://processors.wiki.ti.com/index.php/OMAP3_USB_Detection

    This link has HW instructions specific to the AM3517 EVM but the SW instructions should be generic.
    http://processors.wiki.ti.com/index.php/UserGuideUsbDriver_PSP_04_02_00_07

    This link refers to a really old version of Linux and USB Driver. It does give a good overview of the switch between Host and Device. Ignore the specific commands as the newer versions have changed significantly.
    http://processors.wiki.ti.com/index.php/USB_OTG_on_DaVinci

    All the above requires manual switch and device function loading. I haven't seen much to setup an automatic switch. Vaguely remember it might have to with hotplug scripts.

  • 0 in reply to Norman Wong
    Intellectual 830 points

    I finally found the way to activate the OTG as a host. It is required to load one of a USB Gadget. When the Gadget load, it will create a HCD device, then it can act as a HOST. But when remove the Type-A plug, it cannot switch back to peripheral mode. How can I read back the ID pin status so that I can do a switch manually?

    Regards,

    Colman

     

  • 0 in reply to Colman Lai
    TI__Genius 9460 points

    running "cat /proc/driver/musb_hdrc" will show the value of DEVCTL register. D7 bit of this reg is ID pin status. id D7=0 then ID is grounded if D7=1 ID pin is floating.

    Switching to peripheral is not happening could be due to vbus still on. Vbus can be seen at D[3:4] of DEVCTL register.

    Ajay

  • 0 in reply to Ajay
    Intellectual 830 points

    Thank you for the info.

    I can now detect a change between host and peripheral mode now. For the peripheral mode, I have to detect type of connection, it can be a dc charger or a PC host. For a PC host, I have to umount the internal storage and export to the PC. Is there any possible method to implement it?

    Regards,

    Colman

     

  • 0 in reply to Colman Lai
    TI__Genius 9460 points

    For a DC charger , peripheral will not be enumerated and so there will not be any RESET or SET _CONFIG control command whereas PC host will enumerate the device and will  send  RESET signalling and SET_CONFIG. You can refer drivers/usb/musb/musb_gadget.c and musb_gadget_ep0.c for this.

    Ajay