(Atari) ST-RAM boost WIP

[Badwolf]

Ijor's suggestion is to listen for commands sent to the DMA chip and therefore deduce which address lines are being written to as the data lines are driven.

Not to the DMA chip, but to MMU. All the address registers live in MMU because none of the custom chips (besides Blitter) can drive the address bus. So MMU has to address DRAM directly from internal registers.

You're quite right, the registers for the DMA chip's actions are indeed within the MMU. I don't think that matters conceptually, but it's technically correct.

BW

[ijor]

Writes to ST-RAM cost the same as before but reads end up being super fast
...
You would basically be trading fast reads from screen memory to instead get fast writes to work memory so I guess it's a matter of where the bottleneck lies in each particular game. Updating the screen usually involves a ton of read-modify-writes so it's a bit of a guess really.

Btw, you can make writes to ST-RAM faster as well. You don't wait until the slow write bus cycle at ST-RAM completes, you post it (or them) and they would complete in parallel while the CPU is accessing fastram (which would happen all the time if you shadow whole RAM).

Yeah, I guess this is mostly academic, at least for the time being. Sorry about that. But I'm sure you like this kind of stuff as much as I do :)

[agranlund]

Yeah, I guess this is mostly academic, at least for the time being. Sorry about that. But I'm sure you like this kind of stuff as much as I do :)

I do! :)

I'm absolutely no stranger to finding problems for interesting solutions. To be fair, most of what I've done with my Atari is just that :lol:
I do consider myself a beginner when it comes to hardware though so a lot of times I tend to gravitate toward tackling things in software since it comes easier to me.