FS-UAE: 50Hz mode with Intel/Linux

30 June 2012, 21:25

Hello, I'm running FS-UAE 1.2.1 on 64-bit Linux with Intel graphics. My Thinkpad T61 has a 50Hz graphics mode configured, and when I switch to it, FS-UAE detects it and I get great smooth scrolling. But it runs too fast, like it is really refreshing at 60Hz even though the mode says 50Hz.

Is this a bug in FS-UAE or is the X server lying? I tried making new modelines, turning off EDID, etc. as shown on the page for getting 50Hz with nVidia, but nothing works. Does anybody have Intel graphics and have experience with this? Thanks.

FrodeSolheim · 30 June 2012, 23:09

This is almost certainly not a bug with FS-UAE: Because if the scrolling is perfectly smooth, it means that FS-UAE sucessfully syncs to vblank, and if the game then runs too fast, it means that the vblank rate is > 50Hz.

So if xrandr says you have a 50Hz mode, the X server is most likely lying. It sounds exactly like the problems I had when creating a custom modeline for nVidia -where I got a "frontend" mode @50Hz which mapped to a "backend" mode @60Hz (which doesn't really make much sense, but still.. "frontend" / "backend" modes are terminology used in the nVidia driver). I got the problem fixed in the end with a combination of nVidia driver-specific options.

You can of course (and you probably should) try to run some other OpenGL benchmarking program (with vsync) to verify what refresh rate it runs on.

It is also a good idea to read through /var/log/Xorg.0.log for possible problems. If there is a way to enable extra mode-related logging with the Intel driver, you should enable it. It was a similar option with the nvidia driver which helped me debug my problem.

Ufortunately, I don't have any experience debugging / fixing this problem with Intel graphics.. -Anyone else?

02 July 2012, 21:35

Thanks, I confirmed that it's the X server's problem, because glxgears gives 60fps no matter what mode I'm in.

The xorg intel driver doesn't seem to have as many options as the nvidia. However, it seems like in Windows I really do get 50hz, so there must be some way...

02 July 2012, 23:51

UPDATE: I chatted on #intel-gfx and found out that the i915 driver ignores all modelines and just uses a fixed mode for the internal panel. So it's not going to work

If I get a patch to the driver working I'll let you know

30 June 2012, 21:25	#1
hockpa2e Posts: n/a	FS-UAE: 50Hz mode with Intel/Linux Hello, I'm running FS-UAE 1.2.1 on 64-bit Linux with Intel graphics. My Thinkpad T61 has a 50Hz graphics mode configured, and when I switch to it, FS-UAE detects it and I get great smooth scrolling. But it runs too fast, like it is really refreshing at 60Hz even though the mode says 50Hz. Is this a bug in FS-UAE or is the X server lying? I tried making new modelines, turning off EDID, etc. as shown on the page for getting 50Hz with nVidia, but nothing works. Does anybody have Intel graphics and have experience with this? Thanks.

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30 June 2012, 23:09	#2
FrodeSolheim FS-UAE Developer Join Date: Dec 2011 Location: Førde, Norway Age: 43 Posts: 4,043	This is almost certainly not a bug with FS-UAE: Because if the scrolling is perfectly smooth, it means that FS-UAE sucessfully syncs to vblank, and if the game then runs too fast, it means that the vblank rate is > 50Hz. So if xrandr says you have a 50Hz mode, the X server is most likely lying. It sounds exactly like the problems I had when creating a custom modeline for nVidia -where I got a "frontend" mode @50Hz which mapped to a "backend" mode @60Hz (which doesn't really make much sense, but still.. "frontend" / "backend" modes are terminology used in the nVidia driver). I got the problem fixed in the end with a combination of nVidia driver-specific options. You can of course (and you probably should) try to run some other OpenGL benchmarking program (with vsync) to verify what refresh rate it runs on. It is also a good idea to read through /var/log/Xorg.0.log for possible problems. If there is a way to enable extra mode-related logging with the Intel driver, you should enable it. It was a similar option with the nvidia driver which helped me debug my problem. Ufortunately, I don't have any experience debugging / fixing this problem with Intel graphics.. -Anyone else?

02 July 2012, 21:35	#3
hockpa2e Posts: n/a	Thanks, I confirmed that it's the X server's problem, because glxgears gives 60fps no matter what mode I'm in. The xorg intel driver doesn't seem to have as many options as the nvidia. However, it seems like in Windows I really do get 50hz, so there must be some way...

02 July 2012, 23:51	#4
hockpa2e Posts: n/a	UPDATE: I chatted on #intel-gfx and found out that the i915 driver ignores all modelines and just uses a fixed mode for the internal panel. So it's not going to work If I get a patch to the driver working I'll let you know

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