The myth of the vertical retrace interrupt on EGA/VGA

Discussion about old graphics cards, monitors and video related things.

Re: The myth of the vertical retrace interrupt on EGA/VGA

Postby Scali » 2019-3-04 @ 20:31

SirNickity wrote:Results are mixed enough that you can't count on it being supported, so it wouldn't make much sense to write software that relies on it.


That is the takeaway.
Until I wrote these experimental tools and had people run them on a wide variety of hardware, I had no idea of how broad the support was for this feature.
Now we know that it is indeed not something you can generally count on. I mean, if it was say one in 20 video cards that wouldn't support it, especially if those would be the cheap brands like Trident or Realtek, I could justify using it.
But it seems that even many popular and high-end cards don't support it (or the chips do, but it's not connected on the PCB).

The only thing that's still missing is the results of a real IBM PS/2.
I mean, with 8088 MPH, our justification was that at least all our code worked perfectly on any true blue IBM (5150, 5155 and 5160).
If this feature works relibably on a PS/2, then at least I could create some kind of '8088 MPH' for the PS/2, and use this as one of its defining features.
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Re: The myth of the vertical retrace interrupt on EGA/VGA

Postby Error 0x7CF » 2019-3-05 @ 21:31

I could run it on my IBM PS/1 Model 2011 sometime Friday if you'd like. I'm pretty sure it's VGA and not MCGA.

What I can tell you right now is it doesn't generate interrupts on my Thinkpad 755CS.
It's important to remember that things have to be old before they're antique.
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Re: The myth of the vertical retrace interrupt on EGA/VGA

Postby Error 0x7CF » 2019-3-08 @ 21:43

Zero IRQs out of my PS/1. Then again, it was a value machine so it may not be connected for similar reasoning as IBM's ISA card.
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Re: The myth of the vertical retrace interrupt on EGA/VGA

Postby Scali » 2019-3-08 @ 21:53

Error 0x7CF wrote:Zero IRQs out of my PS/1. Then again, it was a value machine so it may not be connected for similar reasoning as IBM's ISA card.


Thanks for testing, and yes, perhaps you're right.
I suppose the most interesting test would be a true PS/2, ideally the first model to ever introduce VGA (a model 30, 50, 60 or 80 apparently).
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Re: The myth of the vertical retrace interrupt on EGA/VGA

Postby SirNickity » 2019-3-12 @ 21:25

I just won an auction for a Model 30 286. I'll give it a try when I can. Will probably have to wait a couple weeks for shipping, cleaning, and PSU recapping.
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