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TUSB546A-DCI: chip usage question

choonmin Lee
Prodigy 20 points

Part Number: TUSB546A-DCI
Other Parts Discussed in Thread: TUSB546-DCI

Dear TI engineer.

I have a question about TUSB546A usage.

<Our status>

- dp 2 lane + usb3.0 2 lane

- Do not use HPD pin (using PD VDM message)

- TUSB546 I2C mode usage

1. General register setting

EQ_OVERRIDE = 1

HPDIN_OVERRIDE = 1

Q1. Is it correct to set the register with above value?

Q2. When set to HPD_IN is high, what does TUSB546 do?

2. Link training 

Q3. When Displayport dongle is connected, is it correct to set CTLSEL to 10 (4 lane DP) / 11 (2 lane DP + USB3.1)??

Q4. Link training fail does not occur in Apple multiport dongle (simultaneous support for HDMI / USB / Type C), But, ordinary Displayport dongle (HDMI only), Link training fail is occurring.

Do we have to do more setting for TUSB546 register??

3. Aux snooping mode

If using TUSB546-DCI in I2C mode, then system software must disable AUX snooping whenever the CONFIG1 pin is high. (from specification document)

-Current Aux snooping mode is on, and CONFIG1 (CAD_SNK) Pin is not connected.


Q5. Is it correct to turn on Aux snooping when I2C mode, when CONFIG1 (CAD_SNK) Pin is not connected?

  • 0
    TI__Guru 64326 points

    Hi Choomin,

    Q1. Is it correct to set the register with above value?

    • These values are correct when using TUSB546A in this state.

    Q2. When set to HPD_IN is high, what does TUSB546 do?

    • TUSB546A will keep on all the active DP lanes and close the AUX to SBU switch. When HPDIN is Low for greater than 2ms, all DisplayPort lanes are disabled while the AUX to SBU switch will remain closed.

    Q3. When Displayport dongle is connected, is it correct to set CTLSEL to 10 (4 lane DP) / 11 (2 lane DP + USB3.1)??

    • This would depend on the type of DP dongle that has been connected. Typically and ordinary DP dongle would use 4 Lane DP mode.

    Q4. Link training fail does not occur in Apple multiport dongle (simultaneous support for HDMI / USB / Type C), But, ordinary Displayport dongle (HDMI only), Link training fail is occurring. Do we have to do more setting for TUSB546 register??

    • All registers are listed in the datasheet. Do you have a AUX traffic log with ordinary DP dongle? PD controller should change TUSB546A mode based on what is connected. In this case try manually changing to 4 Lane DP mode. 

    Q5. Is it correct to turn on Aux snooping when I2C mode, when CONFIG1 (CAD_SNK) Pin is not connected?

    • If TUSB546A is not in GPIO mode CAD_SNK function is not assigned to pin 29. AUX snooping can be turned on in I2C mode. Turning off AUX snooping will cause all DP lanes to be active at all time (which may be desired) instead of adjusting with the actual DP lane count communicated over AUX.  

  • 0 in reply to Malik Barton57
    Prodigy 20 points

    Dear TI

    I have a question Q6 about Q3 / Q4

    Q3. When Displayport dongle is connected, is it correct to set CTLSEL to 10 (4 lane DP) / 11 (2 lane DP + USB3.1)??

    • This would depend on the type of DP dongle that has been connected. Typically and ordinary DP dongle would use 4 Lane DP mode.

    Q4. Link training fail does not occur in Apple multiport dongle (simultaneous support for HDMI / USB / Type C), But, ordinary Displayport dongle (HDMI only), Link training fail is occurring. Do we have to do more setting for TUSB546 register??

    • All registers are listed in the datasheet. Do you have a AUX traffic log with ordinary DP dongle? PD controller should change TUSB546A mode based on what is connected. In this case try manually changing to 4 Lane DP mode. 

    Q6. If our AP(GPU) only can support 2 lane DP / 2 lane USB 3.1 because of HW limitation,

    should we still control whether 2 lane DP or 4 lane DP depends on sink device by PD controller?? 

  • 0 in reply to choonmin Lee
    TI__Guru 64326 points

    Hi Choomin,

    There can be a conflict with lane count when using the DP dongle. If the Source is restricted to two lanes then we should see this communicated to the Sink in the AUX traffic log. TUSB546A can be put into manual 4 lane DP mode in order to prevent any issues with link training. In this way we can see what effect the dongle has on the link training process.

     We can also look at the AUX bus directly. Please check for the correct common mode voltages on the AUX bus when the DP dongle is connected. AUXP common mode voltage should be around 0.3V and AUXN should be around 3V.

    Also is this DP dongle passive or active dongle? We can only work with DP to HDMI active protocol converter dongle and not the DP++ to HDMI passive adapter dongle.