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[Qemu-devel] How to Simulate hardware that counts scanlines?

From: Steve Ellenoff
Subject: [Qemu-devel] How to Simulate hardware that counts scanlines?
Date: Thu, 27 Jul 2006 03:22:31 +0000

I'm working on some custom emulated hardware to integrate with qemu's full pc emulation ( i guess you could call it a new target, but really just some mods of the x86 )..

I am curious if there's a way I could simulate counting scanlines. Basically a small piece of the chipset I'm implementing has a register that increments on each scanline pass. Since other parts of the chipset setup the timing, it probably uses some kind of formula to determine when to count them, rather than any kind of mechanism that tells it a scanline just completed.. but I've no idea how the thing really works..

The guest os code is polling this register on a very fast interval, and when it detects a certain # of scanlines have been counted, it will swap it's display buffers, ie, it's waiting for the vblank, so it can have nice smooth animations.

What's the best way to approximate this using qemu? Currently, I'm guessing at it, and the animations are choppy.

FYI - this is not using VGA at all, it's all custom programmed via the chipset and the running code.

I'm not all that familiar with vga hardware, so I didn't really see anything like this in there. I'm not sure if it does anything like that or not, but if it does, I guess I didn't see it..

Hope someone has some good suggestions - Thanks!



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