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Hey, I've noticed something odd about emulation of Hercules graphics mode where V-Sync rate appears to be ~100 Hz rather than expected ~50 Hz. This ~100 Hz shown in the GUI matches a small tool I wrote to programmatically measure V-Sync interval as well. 
For context, I'm considering making a game using Hercules and evaluating state of emulation and it's a bit of a mess:
Unfortunately without real hardware I'm not able to work out who's right and who's wrong. Perhaps someone here with access to real hardware would able to run the tool and confirm whether it should run at 50 Hz...? My tester tool w/ source code: |
Replies: 1 comment 3 replies
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That's odd. I checked the 0.4.1 release version and I see 50Hz as expected. If you use the CGA card is it showing 60 correctly? |
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Thanks for checking, yes CGA shows 60 and Hercules text mode shows 50 as expected, the issue is specific to Hercules graphics mode. Just tried it on another PC with Prince of Persia - same 100 FPS result. |
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Found the bug. I'm in the middle of adding PLL-based monitor emulation which is not quite ready to merge yet, but I'll see if I can backport the fix this weekend, it's fairly simple. I would assume 86box has a similar bug - Hercules graphics mode needs a /16 clock divisor, not /8. You may want to open an issue over there. 
your testing scheme can have a 2-3 frame variance due to using the time of day counter, but this seems better. |
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Awesome, thanks a lot! Yes I will let 86Box team know. |
Found the bug. I'm in the middle of adding PLL-based monitor emulation which is not quite ready to merge yet, but I'll see if I can backport the fix this weekend, it's fairly simple.
I would assume 86box has a similar bug - Hercules graphics mode needs a /16 clock divisor, not /8. You may want to open an issue over there.
your testing scheme can have a 2-3 frame variance due to using the time of day counter, but this seems better.