Author: Christophe Theron
Date: 10:27:40 09/29/99
Go up one level in this thread
On September 29, 1999 at 10:01:09, Ratko V Tomic wrote:
>> The windows version seems to be more reasonable as it doesn't stuff
>> an unknown piece of software into memory and hook on to the timer
>> interrupt to check for moves by scanning video memory, etc.
>
>Windows version probably has to use Windows hooks (from Windows API),
>which has much more hook code overhead (on CPU speed) than a DOS hook
>of timer interrupt. This is due to much greater number of instructions
>for context switch in Windows (DOS needs only to push/pop registers)
>as well as protected mode overhead on every interrupt. The overall
>pure Windows background overhead on CPU, as tested with Rebel 8-10
>running in stand-alone DOS vs in Windows DOS Box, with same hash tables
>(of various sizes) under windows, is about 5% drop in speed in DOS Box.
>
>As to checking video memory for moves, that seeems odd thing to do,
>when hooking interrupt 0x10 will do it much quicker, with no CPU
>overhead, other than checking 2 registers only within the individual
>output operation. If a DOS program is meant to run on a variety of
>graphics hardware, it would have to operate via int 0x10 for text
>output, at least in some types of program settings.
You seem to know quite a bit on the PC BIOS. So you should know thete are no
programs anymore that use the crappy BIOS interrupts to write data to the
display. Since more than 15 years.
The interrupts were far too slow and somewhat inadequate for correct display
management. Every DOS software developper as written his own routines, both for
text mode output and graphic mode output.
You can hook the BIOS display interrupt and sit there for as long as you want,
and still receive absolutely no output from the chess programs.
So the ONLY solution is to watch the display memory periodically. In text mode
you would try to locate the played move at a given text position, in graphical
mode I suppose the Auto232 driver tries to sniff which squares have been redrawn
since the last time.
Yes, that's ugly.
Christophe
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