Tinyus Tech

[pink^abyss]

Originally Posted by girv

Great thread, I love this sort of information





Does this mean you queue all blits then, at the correct raster, you busy loop through the queue blit->wait->blit->wait->blit->... ?


Do you loop checking VPOS for the right line to start the queue or use an interrupt?

I'm loop checking VPOS. No interrupts.

Then everything gets blitted.

When starting a blit i turn priority off, because i gather data for next blit and calc clipping. Then i turn prority on and wait for blitter finish. So i can overlap my cpu setup time with the idle blitter cycles. And as i blit only same sized blits one after another, i can leave many blitters regs untouched (once they have been initialized).

[jotd]

a lot of games use busy blitter loops but don't set BPLPRI while they're waiting... Isn't that a waste of time and shouldn't it be fixed with no effort ? Unless it could mess up with interrupt code running (music...)

[zero]

Great, efficient use of the blitter by pink.

I wonder how many games from the 80s and 90s came anywhere close to being this efficient. On the one hand the tools we have now to check things like DMA slot allocation were only a dream back then, but stuff like setting the priority bit and batching up same sized blits was well known, at least in the scene.

I think back then it was hard to get this kind of info or discuss ideas with people. There were BBS and some diskmags, or maybe you could go to a party and try to talk to some people. A lot of my knowledge came from reverse engineering demos and games, and I wasn't that good at it...

[pink^abyss]

Originally Posted by zero

Great, efficient use of the blitter by pink.

I wonder how many games from the 80s and 90s came anywhere close to being this efficient. On the one hand the tools we have now to check things like DMA slot allocation were only a dream back then, but stuff like setting the priority bit and batching up same sized blits was well known, at least in the scene.

I think back then it was hard to get this kind of info or discuss ideas with people. There were BBS and some diskmags, or maybe you could go to a party and try to talk to some people. A lot of my knowledge came from reverse engineering demos and games, and I wasn't that good at it...

Same for me. When we did our Amiga demos in the 90ties it was a lot of guess work with little real knowledge. We had mostly no idea of DMA cycles Now i just hit the profile button in Bartmans plugin and see where those cycles go..

[FSizzle]

Originally Posted by jotd

a lot of games use busy blitter loops but don't set BPLPRI while they're waiting... Isn't that a waste of time and shouldn't it be fixed with no effort ?

Setting BLTPRI can make overall execution slower in various scenarios, depending on how instructions are scheduled and how they compete with DMA.

Since code execution naturally has cycles that don't access the bus, interleaving code and blitter bus access can often be preferable.

Finally, enabling/disabling the flag itself also adds additional cycles.

In the end, you have to profile and see where it makes sense to enable BLTPRI, if at all.