Q: | The example you gave is not a standard screen size, can I use it? |
A: | Why not? There is NO reason whatsover why you have to use 640x480,
800x600, or even 1024x768. The X server lets you configure your hardware
with a lot of freedom. It usually takes two to three tries to come up the
right one. The important thing to shoot for is high refresh rate with
reasonable viewing area. not high resolution at the price of eye-tearing
flicker! |
Q: | It this the only resolution given the 65Mhz dot clock and 55Khz
HSF? |
A: | Absolutely not! You are encouraged to follow the general
procedure and do some trial-and-error to come up a setting that's
really to your liking. Experimenting with this can be lots of fun.
Most settings may just give you nasty video hash, but in practice a
modern multi-sync monitor is usually not damaged easily. Be sure
though, that your monitor can support the frame rates of your mode
before using it for longer times. Beware fixed-frequency monitors! This kind of hacking around can
damage them rather quickly. Be sure you use valid refresh rates for
every experiment on them. |
Q: | You just mentioned two standard resolutions. In Xconfig, there are
many standard resolutions available, can you tell me whether there's
any point in tinkering with timings? |
A: | Absolutely! Take, for example, the "standard" 640x480 listed in
the current Xconfig. It employes 25Mhz driving frequency, frame
lengths are 800 and 525 => refresh rate ~ 59.5Hz. Not too bad. But
28Mhz is a commonly available driving frequency from many SVGA boards.
If we use it to drive 640x480, following the procedure we discussed
above, you would get frame lengths like 812 (round down to 808) and
505. Now the refresh rate is raised to 68Hz, a quite significant
improvement over the standard one. |
Q: | Can you summarize what we have discussed so far? |
A: | In a nutshell:
for any fixed driving frequency, raising max resolution incurs the penalty
of lowering refresh rate and thus introducing more
flicker.
if high resolution is desirable and your monitor supports it, try to
get a SVGA card that provides a matching dot clock or DCF. The higher,
the better!
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