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- From: sip1@ellis.uchicago.edu (Timothy F. Sipples)
- Newsgroups: comp.os.os2.misc
- Subject: SuperVGA Advice from IBM
- Message-ID: <1992Jul25.022246.7331@midway.uchicago.edu>
- Date: 25 Jul 92 02:22:46 GMT
- Sender: news@uchinews.uchicago.edu (News System)
- Reply-To: sip1@midway.uchicago.edu
- Organization: Dept. of Econ., Univ. of Chicago
- Lines: 60
-
- The following comes from Dale Whitfield. Enjoy.
-
-
- SVGA Utility - clearing up some misconceptions.
-
- The svgadata.pmi file is generated by calling BIOS int 10h to set the
- mode. All relevant registers are then read to determine the values
- required to set that mode without using BIOS. The setmode data
- applies to protect-mode sessions only, DOS mode sets always go
- through BIOS. The reasons for using BIOS here should be obvious; to
- set a mode without BIOS we can make no assumptions as to what the
- register values should be, due to the different timing values
- generated by the same chipset on different board implementations etc.
- So this is the option that was chosen. There exists a VESA standard,
- the 'Super-VGA Protect Mode Interface' (SVPMI) which attempts to
- define a standard for such a situation, ie the pmi-file layout, but
- this is lacking and things soon started to get invented to take care
- of the gaps.
-
- The most important assumption is that when the svga utility is run,
- the video adapter is set up correctly as it was when it was installed
- and used under 'pure' DOS including relevant TSRs. This will ensure
- that captured values can be used to accurately set modes and do a
- bunch of other stuff.
-
- Currently the pmi-file is used only for super-vga data, but it is
- theoretically possible to include data for any mode. For example, the
- ISO standard calls for text modes to run at 72/75Hz (I think) which
- is not what OS/2 will currently set. The current BVHSVGA.DLL
- implementation has limitations which won't allow these VGA modes to
- be included, but are possible. Ideally the pmi-file should encapsulate
- all device-dependance, and the interpreter of it (BVHSVGA in this
- case) would just feed on that data.
-
- Some notes on Virtualisation
-
- Performing video virtualisation is a tricky undertaking. Attempting
- to emulate VGA planar modes (16-colour) in software, via say a state
- machine, would be prohibitive in terms of performance. Therefore any
- DOS application that is running in the background, and wants to
- continue to run, must have access to the hardware.
-
- ( DOS Full-Screen (foreground task) - minimal video IO trapped )
- ( DOS Window (background task) - all video IO trapped )
-
- This is possible, but under the tight control of the Virtual Video
- driver which will use the VGA hardware to do so, as well as some
- incestuous goings on with the display driver. With this in mind there
- are obviously going to be some restrictions. The first of these is
- that if the VGA hardware is in a 256-colour mode (linear), it will
- not be possible to have access to it, or change it to a planar mode,
- in order to allow a background planar-mode app to run. The converse
- is, however, not true, mainly because its a simple matter to
- virtualise linear modes without needing hardware assistance.
-
- --
- Get the OS/2 FREQ. ASKED QUESTIONS LIST | Timothy F. Sipples
- from 128.123.35.151, anonymous ftp, | Internet: sip1@ellis.uchicago.edu
- directory pub/os2/all/faq, or from | Dept. of Econ., U. Chicago, 60637
- LISTSERV@BLEKUL11.BITNET (send "HELP"). | Tsongas > Perot > Clinton. Yay.
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