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Is it possible to control I2C switch through TI HDMI DDC channel?

Hai Dong
Prodigy 60 points

Other Parts Discussed in Thread: PCA9548A

Is it possible to use TI HDMI DDC channel to control an I2C switch, for example, PCA9548A?

TI HDMI driver does not seem to provide interface for DDC channel control except reading EDID, am I correct?

  • 0
    TI__Guru**** 170625 points

    Hello Dong,

    Hai Dong said:
    TI HDMI driver does not seem to provide interface for DDC channel control except reading EDID, am I correct?

    It seems to me that TI816x HDMI DDC driver can be used for HDCP purpose only.

    linux-kernel/arch/arm/plat-omap/hdcp_ddc.c

    linux-kernel/arch/arm/plat-omap/include/plat/hdcp_ddc.h

    linux-kernel/arch/arm/plat-omap/hdcp_lib.c

    linux-kernel/arch/arm/plat-omap/include/plat/hdmi_lib.h

    See also the below e2e thread:

    Regards,
    Pavel

  • 0 in reply to Pavel Botev
    Prodigy 60 points

    Pavel, thanks for your reply. are you saying that we can't do I2C type transactions on HDMI DDC line? I know the driver doesn't support this now, but what about we modify the driver if HDMI hardware module can support I2C operation? is this feasible?

  • 0 in reply to Hai Dong
    TI__Guru**** 170625 points

    Hai Dong said:
    are you saying that we can't do I2C type transactions on HDMI DDC line?

    No, this is not what I am saying.

    Hai Dong said:
    I know the driver doesn't support this now

    This is what I am saying.

    Hai Dong said:
    but what about we modify the driver if HDMI hardware module can support I2C operation? is this feasible?

    Yes, I think this should be feasible. I will also double check with the HDMI team and come back to you with their opinion.

    Also you should verify that your I2C switch supports DDC, you can check this in the I2C switch datasheet and also consult in the e2e I2C forum.

    http://e2e.ti.com/support/interface/etc_interface/f/390

    Regards,
    Pavel

  • 0 in reply to Pavel Botev
    TI__Guru**** 170625 points
    We have not tested from that perspective though. Not sure about the electrical aspects and I2C protocol requirements such as bus arbitration (multi-master mode), slaves holding SCL low to throttle master, etc…

    The DDC I2C channel is controlled by the HDMI core since it needs to handle HDCP transactions, hence is not directly accessible as an I2C channel.

    Regards,
    Pavel