VGA write mode 0 display bug

Support and general discussion.
Post Reply
altheos
Posts: 72
Joined: Wed 24 Feb, 2016 7:27 pm

VGA write mode 0 display bug

Post by altheos »

Hello,

I'm using various display tests programs and found what appears to be a bug in PCem's VGA write mode 0.

Testing the VGA "ALU" operations results in incorrect display :
Mode_0_AND_latches.PNG
Mode_0_AND_latches.PNG (11.66 KiB) Viewed 4717 times
Here the test consist of ANDing the CPU bytes (that pass through the "barrel shifter" and the "set/reset" logic) and the latches

It should be like this :
Mode_0_correct.PNG
Mode_0_correct.PNG (8.29 KiB) Viewed 4717 times
Interestingly enough if I remove operation with the latches, display is correct. But that is not the right workaround : maybe the latches values read before are wrong ?

Config Used :
PCem v14 - latest source code compiled under msys2
AMI WinBIOS 486 - NO dynamic recompiler
8 Mb RAM
Cirrus Logic GD5429
No Sound
CD-ROM 4x - 256 Mb IDE Hard Disk
Serial Mouse - No Network
DOS 6.22
Attachments
Write mode 0 AND latches_correct.PNG
Write mode 0 AND latches_correct.PNG (8.29 KiB) Viewed 4719 times
User avatar
SarahWalker
Site Admin
Posts: 2054
Joined: Thu 24 Apr, 2014 4:18 pm

Re: VGA write mode 0 display bug

Post by SarahWalker »

Is the test program you're using here something you can provide? (ie without posting copyrighted material to the forum...)
altheos
Posts: 72
Joined: Wed 24 Feb, 2016 7:27 pm

Re: VGA write mode 0 display bug

Post by altheos »

Hello,

I think the program is copyrighted (at least that's what the program displays when I launch it) and the company is still alive.
Can I send you this by another mean ?

Regards.
Post Reply