OCS discussion

[psxphill]

As for ECS being able to use super high res (1280px) in HAM, Im somewhat sceptical about that. So far as I know the super high res modes are restricted to 2bit colour for ECS. Feel free to correct me if Im wrong though someone.

You're right ECS can only do 4 colours in super hires (1280 @15khz 640@31khz). The colour registers need to be setup in a special way as well because it's a bit of a hack.

[psxphill]

It's a quirk of Agnus/Fat Agnus, I believe. It was fixed in later versions, but unfortunately most/all stock 500s have it.

IIRC agnus didn't support slow ram, it was something that was added for fat agnus. I imagine they wanted to do 1mb chip when moving to fat agnus but the time frame didn't allow for adding another address line to everything. When they got round to it they should have at least supported 4mb or even 8mb. Especially when they shortly afterwards upped it to 2mb anyway.
 
Even though 1mb agnus turned up in a500's, it was really only in the a2000 that it was configured to support 1mb chip. Probably for compatibility as alot of software assumes that 1mb is at $c00000.

[psxphill]

I see, that makes sense. What exactly was the purpose of 1280x256/200 anyway? Very odd resolution.

You need that pixel clock for productivity mode. The sync is programmable, so it would be harder to specifically block that mode than to let you use it.

[psxphill]

i.e. you can change any of three subpixel full range, you'd only have 2 bits for modify as well. How'd you want to use them? Step up / down 1 or 2 little steps?

Yeah 4 bits is not enough to do anything meaningful.
 
It might be possible to play around with HAM in hires on the Amiga using copper for writing the additional bitplane data registers. The copper resolution isn't great but it might be possible to do some funky stuff with it. If you can enable HAM6 in hires but disable the dma for bitplane 0 & 1 then you'd effectively have HAM4. You might then be able to use the bitplane data registers to do brightness control from the copper, which would be interesting.