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Last Post 12 Sep 2014 02:42 PM by  Adam Ford
USB Host interfering with i2c
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Rajesh Tirumala
New Member
New Member
Posts:10


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02 Sep 2014 10:09 PM

    Hi,

    I am trying to bring up the USB communications between two logicpd boards (omap 37xx) sitting on a custom mother board. I am running 2.4.2 BSP.

    USB functionality seems working, I can enable usb0 on each side with RNDIS adapter. However, we do have a camera sensor sitting on i2c bus 3 address 0x48, and its failing to respond to any i2c writes with error code 121 (remote io error). The same sensor works fine, if I don't bring up the USB controllers.

    I do notice that, the MFD twl4030 pmic chip is also using address 0x48 on i2c bus.

    The question is, why / how the USB controllers effect the i2c bus 3 in any way..? Is there is kernel configuration that I am missing to make PMIC chip not to interfere with i2c bus 3..?

     

    Any help is sincerely appreciated.
    Adam Ford
    Advanced Member
    Advanced Member
    Posts:794


    --
    12 Sep 2014 02:42 PM
    The TPS65950 PMIC on the SOM has an integrated USB controller. In order for this to initialize the USB correctly, the processor must communicate over i2c with the PMIC.

    If you have another device on the same I2C bus with the same address, it will conflict. Depending on the camera module you have, some I2C devices allow you to change the address - usually by changing a pull-up/down resistor.

    If that is not an option, you will have to move the camera's I2C interface to a different bus that doesn't have a conflicting address.

    -adam
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