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TPS65982: USB-C Display HPD over PD and DDI over SBU

patrick krekelberg
Prodigy 30 points
Part Number: TPS65982

We have a need to programmatically mock HPD as well as a Display Data Interface which provides and EDID to a host PC. 

1) Is there any reason we shouldn't be able to 'fake' the HPD dialog over the CC line by sending "Attention" packets? Confirmation of success would be the display "blink".

2) Once the HPD is received, is it reasonable to expect the host PC to poll the SBU lines for an unadulterated (beyond polarity) DDI signal? Meaning, in the simplest sense of a VGA/HDMI display, will the PC GPU then be expecting an I2C slave on SBU1/2 ready to provide an EDID?

Thanks all!

  • 0
    TI__Mastermind 36756 points
    Hi Patrick,

    We use the CC lines strictly for PD messaging according to the USB PD spec. However, we have an Alternate Mode where you can send up to 4 unique PDIOs (virtual GPIOs) over the CC lines when a GPIO event is triggered. The SBUs are also used for Alternate Modes in our part. We have an application note on Alternate Modes which may help you. Please refer to it at the link below:
    www.ti.com/.../slva841.pdf

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    Prodigy 30 points

    Thanks Eric, we are specifically aiming to use DisplayPort alternate mode, so I don't think we need any custom PD messaging. 

    My understanding is that if we signal DisplayPort alt mode configuration, and give an HPD "plug" event/IRQ (payload 0x18a), then we should see an SDA/SCL signal on the SBU lines caused by the DFP (a PC/Mac) going into I2C master mode.

    In the simplest case, for example a VGA-to-USB-C adapter which uses PD negotiation on the CC line to enter DP Alt Mode, are SBU lines literally passed directly through to the DDI (just an I2C slave providing an EDID from an I2C EEPROM)?

  • 0 in reply to Eric Beljaars
    Prodigy 30 points
    I am just about certain at this point that our PD messaging for DisplayPort Alternate mode is correct, it matches a VGA to USB-C adapter we bought for comparison purposes. The issue at this point is that we don't get the screen "blink" upon the HPD plug event/IRQ. I know the TX1/RX1 and TX2/RX2 would normally be routed directly through to the DisplayPort device, but since one is not present in our design we need to 'fool' the DFP into thinking there is a display attached. We have TX1/RX1 and TX2/RX2 NC'd, should they be pulled up maybe? Thanks!