Hi!
10--2006 14:49 [EMAIL PROTECTED] (Michael Devore) wrote to
[email protected]:
MD> The loop routine is ANDing the IN DX value with 9 and then looking for bit
MD> 0 (1) match, or reloop. Guess that's an out of vertical, out of horizontal
MD> status check.
No - this is check for "horizontal, but not vertical retrace". Usually,
such check isn't need - there is enough to check if (port&9)!=0 to get any
retrace state. Anyway, check for (port&9)==1 shouldn't hurt.
BTW, some years ago I compute diagram of retraces (how much IN
instructions performed per each stage) on old machine, and get next result:
Vertical resolution = 400
Vertical frequency = 70Hz
Horizontal frequency = 31.0kHz
Graphics index = 413
Frame retraces: ________ ______._____.______
H \_ 13+-2__/ 2+-0 \_ ... _/ 153 _____ 403 \ (5908 INs total)
V _____________________ ... ________/ 26 \_______
As you may see, vertical retrace signal amount isn't too big (26 INs), but
it anyway longer, than horizontal retraces (2 IN per H retrace).
MD> Dunno why it's a problem under Qemu, maybe a BIOS versioning issue.
IN/OUT and BIOS versioning issue?
MD> I suppose it could be an artifact of GDB breaking into the program, but
MD> since Stargunner is an infinite loop at that point, and this would qualify,
MD> I'm thinking it's real.
This may mean only that port emulator code is broken - it not sends
retrace signal or send both H and V simultaneously.
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