Strange display timing issue?

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jebmayers
Posts: 131
Joined: Tue May 10, 2016 11:13 pm
Location: Oxfordshire, UK

Strange display timing issue?

Unread postby jebmayers » Fri Sep 02, 2016 3:05 am

Hi All,

Not sure if this is the best place to post - feel free to move if it isn't!

I have just swapped out my ancient 19" CRT for a slightly less ancient Panasonic plasma that does SoG. It only supports 1280 x 1024 but this is fine for my setup. I have 2 SGI's hooked up to it, my plucky little IRIS Indigo R3K and my Origin 2000 with EMXI/MXE graphics. Both are running at 1280x1024 @ 60Hz.

The IRIS Indigo has no problems at all, it is working fine. The O2K however, has an issue - and I have tried this with 3 cards (2 x SEs, MXE). The problem is this:

When the O2K is booting and shutting down the display is rock solid. As soon as it hits the login screen (IRIX 6.5.22) the display begins to 'jump' slightly by 1 line - like it can't decide which line to start with. There is no pattern to this, sometimes you get a second or so of stability and then it will flick a few times in a second, at other times it is a bit more regular. There is a video change between the console boot sequence and the login screen and then again when you shutdown, so it suggests that IRIX is changing video modes. The plasma TV itself has a few settings like clock phase that I have tried, but I can't seem to dial it out. Interestingly the plasma says it is working at 60.1Hz which makes me suspicious, but this is the same on the IRIS at the same res and the console boot sequence on the O2K.

I don't think this was an issue with the 19" CRT, but then it was so much smaller so maybe it was and I just didn't notice. I will test this later.

Has anyone come across anything similar to this in the past? I tried the xsetmon application and searched here about adding more display modes, maybe this is a possibility.

Any help would be very much appreciated ;o)

Jeb

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Krokodil
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Re: Strange display timing issue?

Unread postby Krokodil » Fri Sep 02, 2016 2:48 pm

Does this problem also cause the screen to be way off center?

My O2 does that with two different models of SOG compliant Dell LCD screens. No such problem on Octane 1, 2, or Alphaserver with VMS. Has no problem with SOG compliant CRT.

Like you describe, it's intermittent, it can be fine for a while, then the next it's out of whack for no clear reason.
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robespierre
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Re: Strange display timing issue?

Unread postby robespierre » Fri Sep 02, 2016 3:44 pm

I'd suspect some kind of grounding or signal integrity issue. Display circuits have something called a "DC restorer" that can make the signals distort if there isn't a solid shared ground.
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jebmayers
Posts: 131
Joined: Tue May 10, 2016 11:13 pm
Location: Oxfordshire, UK

Re: Strange display timing issue?

Unread postby jebmayers » Sat Sep 03, 2016 12:56 am

Thanks for the replies guys.

Krokodil wrote:Does this problem also cause the screen to be way off center?


No - other than the display changing its start position by 1 line it is otherwise correct. This is as rapid change as well - it can happen several times per second.

robespierre wrote:I'd suspect some kind of grounding or signal integrity issue. Display circuits have something called a "DC restorer" that can make the signals distort if there isn't a solid shared ground.


It's possible - I wouldn't rule it out but it seems unlikey. Both machines are going through a KVM switch, and the IRIS Indigo is fine at the same resolution. Also the Origin 2000 is display is fine at this resolution during console startup and during shutdown. There is a noticeable video mode switch between these console startup and IRIX login screen, and again between IRIX and the shutdown sequence and it is during the IRIX 'active' stage where the video signal is unstable.

Jeb

jebmayers
Posts: 131
Joined: Tue May 10, 2016 11:13 pm
Location: Oxfordshire, UK

Re: Strange display timing issue?

Unread postby jebmayers » Sat Sep 03, 2016 5:32 am

So i have tried a variety of video cables, swapped the two around, taken the KVM out of the loop and I get the same result with all combinations. I also dug out my old SoG monitor and can confirm it doesn't happen with that monitor connected so it is definitely something this plasma doesn't like about the signal the Origin2000 is producing - but only in IRIX.

jebmayers
Posts: 131
Joined: Tue May 10, 2016 11:13 pm
Location: Oxfordshire, UK

Re: Strange display timing issue?

Unread postby jebmayers » Sat Sep 03, 2016 1:20 pm

Ok, partial success - I have managed to fix this by creating a custom .vfo file for 1280x1024@59.96Hz. Still work in progress as I have to change the settings on the plasma every time I want to switch between the Origin2000 and the IRIS Indigo. Of course it also looks screwy now when I am booting and shutting down the O2K - proof that it does seem to be using a different video mode for this - even though I am setting 'use as boot default' option in xsetmon.

I am happy at least as I now know I can solve the issue - just needs a bit of refinement ;o)

Jeb

jebmayers
Posts: 131
Joined: Tue May 10, 2016 11:13 pm
Location: Oxfordshire, UK

Re: Strange display timing issue?

Unread postby jebmayers » Sun Sep 04, 2016 12:42 pm

Got this sorted now - I essentially created a reduced blanking vfo for 1280x1024@60Hz for MGRAS SSI, SSE, MXI or MXE boards.

I have attached the vfo and vfs here in case anyone else finds it useful. The vfo should be copied to /usr/gfx/ucode/MGRAS/vof/2RSS/1280x1024_60rb.sdb

Hopefully this will save a some some time if they encounter the same issue.

Jeb

1280x1024_60rb.vfo
(6.41 KiB) Downloaded 9 times

1280x1024_60rb.txt
(1.12 KiB) Downloaded 11 times
.vfs file renamed to .txt so I could attach it.


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