Using PowerStrip to get 50Hz Windows display mode on laptop screen

[mark_k]

Hi,

This isn't strictly WinUAE-related, but I figure someone here might know more about this than me.

I want to set my laptop's display to 50Hz, so the WinUAE display is as smooth as possible. Originally I assumed that would be impossible because the laptop screen would be fixed at 60Hz, so there would always be glitching in scrolling & animation due to the difference between the Amiga 50Hz rate and the laptop screen 60Hz.

However, I downloaded PowerStrip from Entech Taiwan, and amazingly enough it allowed me to adjust the refresh rate of the laptop's screen to 50Hz, so I can now get almost perfectly-smooth graphics.

I was able to set the refresh rate anywhere between H 11.817 kHz / V 11.086 Hz (very flickery!) and H 96.901 kHz / V 90.902 Hz. That wide range surprised me. Very low frame rates start to flicker; at 30Hz the flicker is just noticeable, worse when the refresh rate is lower. I'm not sure exactly why that is -- maybe the LCD backlight is driven at twice the frame rate???

Anyway... as I said I have been able to set the refresh rate to 50Hz. If the PC refresh rate doesn't exactly match the emulated Amiga rate (e.g. PC rate 50.1Hz), there is a minor glitch in the Amiga output when WinUAE is in windowed mode. The "glitch line" is most easily seen when running a program that scrolls the whole screen horizontally. It moves up or down depending on whether the PC refresh rate is higher or lower than the emulated Amiga rate. So far the best approximation I have come up with is 50.2Hz, which makes the glitch line move very slowly. [If there were a "Windowed + VSync" mode in WinUAE, that should remove the glitch completely.]

What is the exact refresh rate of a real PAL Amiga? How many clock cycles are there per frame?

Also, how would I add a 50Hz mode to the modes that Windows recognises? Currently I can only select 60Hz modes using the nVidia control panel.

[Rabbit80]

Are you running Vista by any chance? I get exactly the same effect with Vista - however running under XP it is perfect @ 50Hz + vSync...

[mark_k]

Originally Posted by Rabbit80

Are you running Vista by any chance? I get exactly the same effect with Vista - however running under XP it is perfect @ 50Hz + vSync...

Yes. But the glitch I mentioned happens in windowed mode only. When in full-screen mode, even non-vsync seems to be glitch-free. In full-screen vsync mode there is no glitch at all.

That type of glitch is inevitable unless the PC output is synced to the vertical blank, since the PC refresh rate will never exactly match the emulated Amiga refresh rate. That's why I wondered whether a windowed+vsync mode is possible; it should eliminate glitches in windowed mode.

[Toni Wilen]

Originally Posted by mark_k

That's why I wondered whether a windowed+vsync mode is possible; it should eliminate glitches in windowed mode.

It isn't possible. (at least not reliably)

[alexh]

Interesting I did not think it was possible to set laptop LCD panels to a rate as low as 50Hz!

[mark_k]

Originally Posted by alexh

Interesting I did not think it was possible to set laptop LCD panels to a rate as low as 50Hz!

Neither did I. (And my panel went right down to a very-flickery 11Hz!)

It probably depends on the specific LCD panel and the graphics controller. If it's of any use my laptop has a nVidia GeForce Go 7300 (a fairly low-end chip). The panel is made by LG Philips LCD, model LP154W02-TL09.

It would be interesting if other people could test their laptop or desktop LCD screens with PowerStrip and report whether they support 50Hz display.

In Windows, you can use Entech's MonInfo tool to read and display the panel EDID data. So you can find the panel make and model without taking the monitor/laptop apart. Note that the same laptop model might use several different LCD screens, so it's important to have the panel info, not just a laptop or monitor model number.

[OddbOd]

I'm not all that surprised by your results mainly because one of the ways to extend battery life in a laptop is to lower the duty ratio of the inverter that supplies the backlight. The datasheet for your panel specifically mentions that it should work down to a 15% duty ratio which by my rough calculation is around the 9Hz mark, pretty close to what you actually observed.

Unfortunately my own LCDs are older (2003 vintage mfd by Chi Mei Optoelectronics) desktop models and refuse to go any lower than 56Hz, drat.

[chiark]

i wish I could help...

I've installed powerstrip, created a 50Hz 1280x768 mode, the driver accepted it... And I'm still running at 60hz, even though powerstrip says that it's forcing 50hz. winuae in fullscreen vsync syncs perfectly - at 60Hz!

Annoying!

Tried creating a new monitor, but the only thing that seems to take is 60Hz.

The laptop is a toshiba libretto u100...

[mark_k]

Originally Posted by OddbOd

I'm not all that surprised by your results mainly because one of the ways to extend battery life in a laptop is to lower the duty ratio of the inverter that supplies the backlight. The datasheet for your panel specifically mentions that it should work down to a 15% duty ratio which by my rough calculation is around the 9Hz mark, pretty close to what you actually observed.

I don't think the duty cycle of the backlight is the causing the flicker, rather the frequency of the switching. Looking at the LP154W02-TL10 datasheet (which I found using Google - do you have the datasheet for the LP154W02-TL09?), it gives the typical backlight frequency as 60kHz. I'm guessing that the light is switched at around 10kHz, which is about the same as the horizontal scan rate at its lowest.

Interestingly, the data sheet I have shows the EDID data having two timing descriptors, one for 60Hz (the first/preferred one), the second for 50Hz. My panel's EDID did not have the second descriptor.

Originally Posted by OddbOd

Unfortunately my own LCDs are older (2003 vintage mfd by Chi Mei Optoelectronics) desktop models and refuse to go any lower than 56Hz, drat.

Have you tested the frame rate range that they will accept using PowerStrip's real-time adjustment figure?

Originally Posted by chiark

I've installed powerstrip, created a 50Hz 1280x768 mode, the driver accepted it... And I'm still running at 60hz, even though powerstrip says that it's forcing 50hz. winuae in fullscreen vsync syncs perfectly - at 60Hz!

Annoying!

Tried creating a new monitor, but the only thing that seems to take is 60Hz.

The laptop is a toshiba libretto u100...

Can you use the Entech monitor info tool to read your LCD panel's EDID data and post it here?

The problem might be that, even though you created the new mode, the driver always uses 60Hz, because the panel's EDID data says that is what it prefers.

I had this kind of problem the other day, when I was trying to get a 50Hz desktop in Linux. It seemed no matter what options or modeline I put in xorg.conf, the display was either 60Hz (or completely corrupted/trashed). There would *probably* have been a modeline and options that worked, but in the end I got around the problem by reading the EDID data from my panel, and modifying it so the preferred timings were for 50Hz frame rate. (The nVidia X driver has an option to read EDID data from a file instead of from the display.) That did the trick.

Rather than creating a new mode, try using PowerStrip's real-time adjustment feature. Click its system tray icon, select Display Profiles -> Configure..., then select Custom timing for refresh rate and click Advanced timing options... Check the Real-time adjustment box and try reducing the pixel clock. See how low you can get the refresh rate to go.

[chiark]

Hi Mark, tried that and it won't let me change a thing at all on the fly - everything is enabled, but nothing can be changed!

EDID data attached (binary form). Any clues appreciated, as I'm not at all familiar with the intricacies involved here!

I did try creating a custom driver using pstrip, however that doesn't appear to have affected anything. Does the EDID data override the driver I wonder?

[OddbOd]

@mark_k: Looking at it again I think you're right. Sorry I don't have the datasheet for the rev. 9 and was probably looking at the same one you found via Google, a powerpoint from screencountry.com.

Originally Posted by mark_k

Have you tested the frame rate range that they will accept using PowerStrip's real-time adjustment figure?

Yeah that's what I did without success as soon as it goes below about 56Hz (which is the lowest refresh of any pre-defined so no surprise really) I get an out-of-range message in a fetching shade of red. I had better luck with my brother's notebook which easily scanned down to 19Hz before starting to flicker.

[mark_k]

Originally Posted by chiark

Hi Mark, tried that and it won't let me change a thing at all on the fly - everything is enabled, but nothing can be changed!

EDID data attached (binary form). Any clues appreciated, as I'm not at all familiar with the intricacies involved here!

I did try creating a custom driver using pstrip, however that doesn't appear to have affected anything. Does the EDID data override the driver I wonder?

It may well be that the Windows video driver checks the EDID data and always uses that to validate/override any other setting.

I looked at your EDID data, and there is only one timing descriptor, which says:
Pixel clock 81MHz
Horizontal active 1280 pixels, blanking 408 pixels
Vertical active 768 lines, blanking 34 lines
Horizontal sync offset 48 pixels, pulse width 112 pixels
Vertical sync offset 3 lines, pulse width 6 lines

Those figures give a refresh rate of about 59.83Hz. The pixel clock which gives the nearest to a 50Hz refresh rate is 67.69Mhz (giving a refresh rate of 50.0009Hz).

I have attached a modified version of your EDID data. I changed the first descriptor to give a 50Hz refresh rate, and added a second descriptor identical to your original one. (There is space for up to 4 descriptor blocks, but there's probably not much point in anything other than 50Hz and 60Hz.)

How to get Windows and/or the video driver to recognise that is another matter. Windows stores EDID information in the registry, so it would be a good idea to use regedit.exe to change the info there to the new data.

Also there is an article about setting the refresh rate (albeit in Windows 95/98) at http://www.microsoft.com/whdc/archive/refresh.mspx. Maybe that still applies to Windows XP? This forum thread mentions downloading Intel embedded graphics drivers which contain a tool to modify your video BIOS. That could be worth trying. The registered version of PowerStrip may be able to write the modified EDID back to your panel.

I read on another page that the nVidia Windows driver supports overriding the panel EDID data by adding a certain registry key. I might try that to see whether it means I can select 50Hz modes in addition to all current 60Hz-only resolutions. (Not much use for you, since your laptop uses Intel graphics.)

[chiark]

Mark, thanks so much for your help. I'll give it a try, and I'll also read up on the intricacies of this - it'd be great to get this working!

[mark_k]

Originally Posted by Toni Wilen

It isn't possible. (at least not reliably)

[About whether a windowed + vsync mode is possible]

Does that apply to both Direct3D and OpenGL rendering?

At least in Wine/Linux I was able to successfully use v-synced OpenGL output; there's an option to force vsync in the nVidia driver. Doing that, the "glitch line" that I mentioned was fixed about 1/8 of the way down the screen. Moving the WinUAE window a little way down from the top of the screen gave a perfectly smooth display. Is there any chance you can add a config file option to enable a windowed + vsync native output setting since it does work in some cases? (User would manually add a line to the config file, then the extra option would appear in the drop-down menu in the GUI.)