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TUSB564: DP Alt Mode - how do DPCD registers and snooping come into play with regards to the spec and cross-points?

Lauren Mayfield
Expert 7985 points
Part Number: TUSB564


Hi team,

My customer is just getting into this DP Alt Mode stuff – and they are looking to support DP1.4, 4K60, with USB3(5Gbps) concurrently.

They are a little confused on how DPCD registers and snooping come into play with regards to the spec and the cross-points. They are also unsure if they should be adjusting DPCD registers on their DP-to-HDMI converter (essentially sink) to set MAX_LANE_COUNT = 2, when they are in 2-lane mode.

Can you provide any feedback or materials that would be helpful to them?
Thanks,
Lauren

  • 0
    TI__Guru**** 180041 points

    Lauren

    The TUSB564 manages the number of active DisplayPort lanes based on the content of the AUX transactions. The TUSB564 snoops native AUX writes to DisplayPort sink’s DPCD registers 0x00101 (LANE_COUNT_SET) and 0x00600 (SET_POWER_STATE). TUSB564 disables/enables lanes based on value written to LANE_COUNT_SET.

    So when the TUSB564 is being configured as USB + 2 DP lanes, you are absolutely correct that the DP-to-HDMI converter needs to set its MAX_LANE_COUNT to 2. This will force the DP source to be in 2 DP lanes mode, so now the lane count is consistent among the source, the TUSB564, and the sink.

    Thanks

    David