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Intel HD 4000 and three monitors

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  • #16
    Originally posted by duderino View Post
    Not sure what that means (three different clocks? -- I know that this should not be possible).
    Note that there is an active DP adapter in question. Could it be that DP adapter uses different settings and xrandr show actual status of display (not the the settings of the link that drives DP adapter) ?

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    • #17
      Originally posted by chrisb View Post
      Interesting, I would have thought that your config would require 3 pixel clocks since you have the two 1600x1200 on different outputs (DP & DVI).
      I think it depends on the so called crtc thingy and as far as I know you can configure them arbitrarily with xrandr:

      xrandr --output HDMI1/HDMI2/etc. --crtc 0/1/2

      or something like that.

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      • #18
        Originally posted by nadrimajstor View Post
        Note that there is an active DP adapter in question. Could it be that DP adapter uses different settings and xrandr show actual status of display (not the the settings of the link that drives DP adapter) ?
        Probably, the active adaptor is converting the protocol but the end device is still visible to query resolution etc. As far as I understand, DisplayPort monitors do have a pixel clock, but that clock is encoded inside the DisplayPort datastream which has a fixed (162/270/540 MHz) clock. So DisplayPort only requires one clock regardless of number of connected DP monitors.

        Originally posted by duderino
        Not sure what that means (three different clocks? -- I know that this should not be possible).
        What does "xrandr --verbose |grep CRTC" show? It is possible that there is an extra crtc chip on the motherboard (like Sapphire do with their FleX video cards). I can't think of anything else - you have a DisplayPort and two HDMI ports with completely different resolutions and it works.

        Also, I wonder why xrandr is reporting 6 ports (HDMI1 HDMI2 HDMI3 and DP1 DP2 DP3) when the board only has 3 external ports (HDMI DVI DP)?

        Oddly, I haven't actually found anything in the Intel documentation that suggests it is even possible for two DVI/HDMI ports to share a clock when the monitors are identical, but reports from xorg bug tracker and mailing list say it is. The Intel documentation insists that either one port must be eDP directly from the CPU, or two ports must be DP from the PCH. Weird that Intel don't even mention the possibility of an identical monitor setup, perhaps they don't want to confuse the issue by acknowledging that three monitors off HDMI/DVI can work but only with certain monitors.

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        • #19
          Output of xrandr --verbose|grep CRTC
          Code:
          	CRTCs:      0 1
          	CRTC:       0
          	CRTCs:      0 1 2
          	CRTCs:      0 1 2
          	CRTCs:      0 1 2
          	CRTC:       1
          	CRTCs:      0 1 2
          	CRTC:       2
          	CRTCs:      0 1 2
          	CRTCs:      0 1 2
          Might this indicate that my mobo indeed has an additional chip onboard?
          The first "CRTCs" belongs to the VGA1 output, so maybe this output can only use CRTC chips 0&1 whereas the others can use 0,1 or 2? I have no clue ...

          Anyway before getting this active DP->DVI adapter, I had limited success with driving the 3 displays via VGA+DVI+HDMI. I could get all 3 of them running as cloned displays at 1024x768.
          But when changing the resolution of either of them, one blacked out or the whole machine froze (maybe because VGA can only access two of the three crtc chips?).

          Originally posted by chrisb View Post
          What does "xrandr --verbose |grep CRTC" show? It is possible that there is an extra crtc chip on the motherboard (like Sapphire do with their FleX video cards). I can't think of anything else - you have a DisplayPort and two HDMI ports with completely different resolutions and it works.

          Also, I wonder why xrandr is reporting 6 ports (HDMI1 HDMI2 HDMI3 and DP1 DP2 DP3) when the board only has 3 external ports (HDMI DVI DP)?

          Oddly, I haven't actually found anything in the Intel documentation that suggests it is even possible for two DVI/HDMI ports to share a clock when the monitors are identical, but reports from xorg bug tracker and mailing list say it is. The Intel documentation insists that either one port must be eDP directly from the CPU, or two ports must be DP from the PCH. Weird that Intel don't even mention the possibility of an identical monitor setup, perhaps they don't want to confuse the issue by acknowledging that three monitors off HDMI/DVI can work but only with certain monitors.

          Comment


          • #20
            Here is the output of xrandr --verbose|grep CRTC
            Code:
            	CRTCs:      0 1
            	CRTC:       0
            	CRTCs:      0 1 2
            	CRTCs:      0 1 2
            	CRTCs:      0 1 2
            	CRTC:       1
            	CRTCs:      0 1 2
            	CRTC:       2
            	CRTCs:      0 1 2
            	CRTCs:      0 1 2
            Might this indicate that my mobo indeed has an additional chip onboard?
            The first "CRTCs" belongs to the VGA1 output, so maybe this output can only use CRTC chips 0&1 whereas the others can use 0,1 or 2? I have no clue ...

            Anyway before getting this active DP->DVI adapter, I had limited success with driving the 3 displays via VGA+DVI+HDMI. I could get all 3 of them running as cloned displays at 1024x768.
            But when changing the resolution of either of them, one blacked out or the whole machine froze (maybe because VGA can only access two of the three crtc chips?).

            Comment


            • #21
              Originally posted by duderino View Post
              Anyway before getting this active DP->DVI adapter, I had limited success with driving the 3 displays via VGA+DVI+HDMI. I could get all 3 of them running as cloned displays at 1024x768.
              But when changing the resolution of either of them, one blacked out or the whole machine froze (maybe because VGA can only access two of the three crtc chips?).
              Here is my hw spec and some details from previus post
              Looks like that I we had similar problems.
              I've been bugging manufacturer via email and first I've been told by an engineer that I must have EXACTLY the same monitors for triple configuration.
              Testing that statement in Win7 confirmed that I can't use passive HDMI-DVI adapters and can be different monitors but same resolution (different resolution introduces flickering).
              OK, there is also a LVDS support, so I had to ask is this motherboard any special from referent design... And another engineer replies:
              1. Use Ivy Bridge CPU
              2. 2 HDMI + DVI / 2 HDMI + VGA / 2 HDMI + LVDS
              3. Must have driver support
              HDMI is a transfer from DP port of Intel PCH

              Tested today Ubuntu 13.04. Everything works out-of-the-box. Even passive HDMI-DVI adapters.
              OK... Almost everything... HDMI audio is broken (just in Ubuntu's kernel... that unity icon clockwise swirly thingy is more important than kernel bugs... Nice touch )

              Tomorrow I will test different monitors and TVs to see is there some limitations.

              Comment

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