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LCr4500:About VSYNC mode operation in RGB interface

Masayuki Iwata
Intellectual 710 points
Other Parts Discussed in Thread: DLPC350

Hi,
I input the video signal at 912 x 1140 @ 72 Hz into the HDMI of LCr4500.
The setting conditions are as shown in Figure 1.

Firure 1.

The video source is a combination of a desktop PC and a graphics card.
As shown in Fig. 2, the video information on the GUI is recognized at 912 x 1140 @ 72 Hz. When observing the projection, it is projected at almost 72Hz every frame.

Figure 2.

 

When I changed the video source to raspberry pi 3, as shown in Fig. 3, the interval between the projected frames became wrong. What is wrong?
For reference, we show the video settings of raspberry pi 3.

Figure 3.

 

Raspberry Pi 3 video setteings

 framebuffer_depth=24
 hdmi_force_hotplug=1
 config_hdmi_boost=4
 hdmi_cvt=912 1140 72 1 0 0 0
 hdmi_group=2
 hdmi_mode=87
 hdmi_drive=2

 

Best regards,

Masa

  • 0
    TI__Mastermind 30600 points
    Hi Masa,

    This looks like an issue with the Rasp Pi 3 and the way it outputs video. Perhaps the VSYNC signal is not clean and the Lightcrafter is being triggered differently than you expect. Unfortunately, there is not much support I'm able to offer here because the system is working with a regular graphics card and we are not RPi3 experts.

    My advice would be to measure the VSYNC coming from the graphics card and the RPi3 to see if they match. Make sure the RPi3 is actually behaving the way you would like it to. It seems thought that your Lightcrafter is working well, it's just responding to two different types of video inputs.

    Best,
    Paul
  • 0 in reply to Paul Goedeke
    Intellectual 710 points

    Hi Paul,

      Thank you for answering. Your answer is that the Lightcrafter may not have been triggered as expected, but as far as the video info on the GUI is concerned, it seems that Rasp Pi 3 input  also recognizes 912 x 1140 @ 72 Hz. Nevertheless, I do not understand the reason why the projection period is faster.

    The difference between the graphics card and Rasp Pi 3 is that the VSYNC width and the blanking lines are different. Refer to the figures below. Do these differences affect the rate of projection? Which document describes the blanking rule of the video signal input to Lightcrafter?

    Best regards,

    Masa

  • 0 in reply to Masayuki Iwata
    Intellectual 710 points
    Hi Paul,

    additional information.
    I set the graphics card to the same frame rate and blanking lines as Rasp Pi 3.
    When this video input to Lightcrafter, it became the same output as Rasp Pi 3 (as in figure 3).
    In this state, when only the frame rate was changed from 71.9 Hz to 72 Hz, projection became the expected 72 Hz rate.
    What you can see from this result is that it does not depend on the VSYNC width and the number of blanking lines,
    and that only the frame rate is affecting the projection.
    Now, what is the range of frame rates that Lightcrafter allows?
    For example, what is the tolerance range for the frame rate of 72 Hz?

    Best regards,
    Masa
  • 0 in reply to Masayuki Iwata
    TI__Mastermind 30600 points

    Hi Masa,

    Thank you for the further information. For information on what video parameters are acceptable, take a look at the DLPC350 datasheet. Section 6.11 has the information you are looking for.

    In general, the Lightcrafter allows anything up to 120Hz frame rate. We have seen that there can be issues at certain frame rates as you described and tweaking it as you did it what we recommend to solve the problem. I don't know off hand what the tolerance is, but the device is fairly sensitive to syncing with the video source.

    -Paul

  • 0 in reply to Paul Goedeke
    Intellectual 710 points
    Hi Paul,

    Thank you for answering.
    I checked the datasheet. VBP of the input video signal does not meet the requirement.
    (requirement is 370us, but the input video is about 240us).
    But, it seems to be projected correctly. why?
    Other specifications than that, I think input video blanking meets the data sheet requirements.
    However, there is no description about the frame rate.
    I want to know the specific allowable range of the input frame rate.
    For example, 72 Hz ± xx%.
    By the way, as a result of confirmation, when the input frame rate was 71.95Hz - 73.00 Hz,
    it was projected accurately at 72Hz.

    Best regrads,
    Masa
  • 0 in reply to Masayuki Iwata
    TI__Mastermind 30600 points
    Hi Masa,

    We haven't characterized the Lightcrafter 4500 system for the parameter you are looking for (72hz +/- xx%). The best approach that I can suggest is to do like you are and tweak the video input settings until you get the performance that you are looking for.

    -Paul
  • 0 in reply to Paul Goedeke
    Intellectual 710 points
    Hi Paul,

    Thank you for answering.
    I understood.

    Best regards,
    Masa