Emc vs modern lcd monitors

[Alex Deucher]

2011/8/15 gene heskett <gheskett at wdtv.com>:
> On Monday, August 15, 2011 06:07:09 PM Alex Deucher did opine:
>
>> 2011/8/15 gene heskett <gheskett at wdtv.com>:
>> > On Monday, August 15, 2011 04:20:49 PM Mark Wagner did opine:
>> >> On Sat, Aug 13, 2011 at 05:50, gene heskett <gheskett at wdtv.com> wrote:
>> >> > Greetings all;
>> >> >
>> >> > One of the problems that was confusing me recently is that I had
>> >> > replaced the old samsung crt monitor with a much newer cheap AOC
>> >> > lcd that runs at 1360x724 at best, but under the vesa driver on an
>> >> > ati x1650 video card, it apparently is running in 1024x768. آ This
>> >> > results in a pixel that is far from square unless I use a button
>> >> > on the monitor which shrinks the display sideways, leaving 2" wide
>> >> > black stripes on the sides.
>> >> >
>> >> > From Xorg.0.log:
>> >> >
>> >> > (II) VESA(0): SAMSUNG: Using hsync range of 30.00-81.00 kHz
>> >> > (II) VESA(0): SAMSUNG: Using vrefresh range of 55.00-75.00 Hz
>> >> > (II) VESA(0): SAMSUNG: Using maximum pixel clock of 90.00 MHz
>> >> > (II) VESA(0): Not using mode "1360x768" (no mode of this name)
>> >> > <---native
>> >>
>> >> Looks to me like the server is telling you it doesn't know how to
>> >> generate a resolution of 1360x768.  If this was a CRT, I'd say to
>> >> provide a custom modeline in the xorg.conf file.  Since you've got a
>> >> LCD, I don't know if this is the correct solution or not.
>> >
>> > None of my machines have an xorg.conf with a sample modeline for that.
>> >
>> > Could someone post an example I could try please?
>> >
>> > Or even better, are there docs someplace that would describe how to do
>> > that?  I just looked at the modeline description in a man xorg.conf,
>> > and that lacks the specifics I'd need to make a quasi-intelligent
>> > first guess.
>>
>> The problem with vesa is that you are limited to standard vesa modes
>> that are implemented in the vbios.  You cannot define arbitrary modes.
>>  For that you need to use a real driver specific to your video chip.
>>
>> Alex
>
> I was afraid of that Alex.  And I tried some Modelines suggested on the EMC
> mailing list & got thrown under the bus just as it was leaving.  This
> application that must run, is a realtime application with a base loop of
> its i/o running every 20-40 u-secs.  _NO_ "real" driver allows that,
> wrecking carving of parts in wholesale numbers because the IRQ's that drive
> this apps base thread can be locked out by the "real" driver for intervals
> in excess of 100 milliseconds.  The 'vesa' driver is the only driver that
> allows the base thread to keep some semblance of a steady beat.
>
> This particular card is an ATI X1650.  Does it perchance have an available
> vesa bios update that would add some of the 16x9 modes like this?

Not likely.  I don't think vesa ever officially added any 16:9 modes
as standard vesa modes.  Have you tried turning off acceleration?
Add:
Option "NoAccel" "True"
in the device section of your xorg.conf.  That should significantly
reduce the number of irqs generated.

Alex