Dragon board 410c hdmi startup on win iot


#1

We have a dragon board 410c running win IOT with the default app running.
It is connected to an HDMI touch screen.

We notice the following behavior:
If the HDMI screen is powered up first; when the dragon board powers up
windows boots up and displays on the screen just fine.
However if both are powered up simultaneously, or if the dragon board is powered up first,
then the dragon board does not show any output on the screen.

Is this a known behavior? If so, is there a software level switch or setting that can control this behavior?
We are aware that the HDMI screen produces a 5v signal while it’s on, which the dragon board is likely able to detect.


Increasing HDMI Boot Time
#2

Hi @Dave:

There are numerous possibilities for the cause of this problem. First a little background on what happens between the 410c and the HDMI monitor during power-up.

  • As the 410c powers up it provides 5V to the monitor.
  • there is a ‘Hot Plug Detect’ (HPD) signal in the cable when the monitor is ready it sets HPD to 5V.
  • sometime after the 410c receives the HPD signal it queries the monitor over the DDC lines (similar to I2C protocol) to determine what the monitors display capabilities are.
  • the monitor responds with a list of capabilities (example 480p, 720p, 1080i. 1080p, 1080p60 etc).
  • the 410c them programs the display controller to generate the appropriate display resolution.
  • the HPD signal also gets set when you plug the monitor cable into the 410c. The change in HPD is detected and the 410c starts the query/response sequence to determine what has been plugged in.

During the sequence there are a few things that could go wrong

  • the monitor is supposed to take the 5V from the HDMI connector to power the query response circuit and should provide a response even if the monitor is powered down. Unfortunately many monitors use their own power supplies to power this circuit. If your monitor has done this and is not ready to respond at the time the 410c makes the query then the 410c will think there is no monitor attached. In theory if you r monitor does this it can work around the problem by not asserting the HPD signal until it is ready.
  • the monitor may be providing the HPD signal as soon as it powers up and is not waiting for the 5V from the 410c before providing HPD. The 410c may then miss the HPD transition and fail to start the query/response sequence.
  • The HDMI cable you are using may violate the spec, one of the ways that they can save money is to not route the HPD signal from the monitor to the 410c (one less wire is less copper and hence cheaper). instead the cable manufacturer simply ties 5V to HPD at the ends of the cable.

My highest suspicion would be a problem with your cable, or possibly with the monitor, have you tried other HDMI cables and monitors? Does it work if you power up both at the same time with the cable disconnected and then plug in the cable (the HPD scenario)? At a lower level of suspicion it could be a 410c SW problem, have you tried the same thing using Debian instead of Win10-IOT on the board?

Full Disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.


#3

I don’t think so. Same problem here. With lots of cables and monitors. I suspect that Dragonboard only turn on HDMI when detects some kind of signal on it. Simultaneously turn on doesn’t give enough time to monitor to send signal through HDMI. So, for me, is a Dragonboard issue. Is there a way to avoid this or some kind of firmware fix? Thanks