VOGONS

Search

Common searches

Matrox Millennium in DOS - jittering in 800x600 (and in lowres with UniVBE)

Topic actions

First post, by wbc

Posted on 
User metadata
Rank Member
Rank
Member

Hi all,
I have been used my Matrox Millennium for years in my P200MMX box (paired with S3 Trio3D/2X sometimes for lowres VESA stuff) and i have noticed jittering issues in 800x600 32bpp in DOS (lower bit depths works fine). With UniVBE 6.53 (5.3 doesn't work correctly), things are becoming more interesting! 😀

ZSUjXsfl.jpg

// here goes a bit of technical thoughts, which may be incorrect (or not 😀)

As SDD adds lowres support, and Millennium is a pretty tricky in terms of low-level display interacting (i.e. it features an limited amount of available screen pitches (or bytes per scanline), probably multiples of 128 (VESA modeinfo report without or with UniVBE), confusing a lot of programs), no doubts you will never achieve full 100% compatibility. So with SDD 320x200 32bpp jitters with any refresh rate, with 320x240 it occurs when vertical rate drops below 65 Hz, same for 800x600.
All of there somes have non-exact pitches (not (width*bytes_per_pixel) == 1280 but rather 2048 or something like that) so, as I suspect, jitter is caused by memory to RAMDAC interface or timing issues (in VESA and hires modes in general pixel data goes from memory directly to RAMDAC, bypassing graphics controller, which is only generating sync timings and memory addresses).

Besides that, Matrox is of course barely usable for hardcore VGA/VESA stuff, being more suitable for hires and accelerated 2D graphics under Windows and so on 😉 so no worries anyway from me

Any other suggestions?

--wbcbz7

Reply 1 of 3, by Jepael

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie
wbc wrote:

Any other suggestions?

If you have a TFT monitor, try a different one?
Maybe the signal is something a TFT can't lock on properly, but CRTs have no issues.

Reply 3 of 3, by Jepael

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie
wbc wrote:

Ah, yes, I've tried on LG L1510S and L1919S and both of them experienced these issues (didn't have an CRT to test on it)

Did you try the clock adjust and clock phase settings?
Also, is there an info button to let us know what the monitor thinks about what the signal is?

Most TFTs can only support the standard signals so it can sample it with pixel perfect clock, and thus any deviations from standards can cause issues.

With TFTs, there is also little point using higher non-standard refresh rates anyway, as they don't flicker like CRTs do.

320x200 @ 75 Hz is not standard, so I have no clue how it is sent by video card (most likely doublescanned), and how would a TFT try to receive it (it has to come up with a number how many pixel clocks per line there is)

So my suggestion is that if you just use standard refresh rates, do the TFTs work properly?

Just take a look at the monitor manuals for the list of preset modes.

320x200@70 is really 640x400@70 graphics mode with double pixels and double scanlines, but monitors may regard that as 720x400@70 text mode so it won't be pixel perfect anyway,
320x240@60 is really 640x480@60 graphics mode.

800x600 should be supported at 56/60/72/75Hz by your monitor, but it will be exact by default only if it is sent out with the exact standard.

Go to top of page Go to top of page
Back to Video
Close window
Close window