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Forums > C64 Coding > Ultimax unleashed..
2019-11-21 10:59
andym00

Registered: Jun 2009
Posts: 44
Ultimax unleashed..

Well, someone did what I've been wanting to do for some time.. Driving VIC fetches from external memory, and stuffing register writes over the bus.. Hooray for Ultimax mode I guess :)

Always wanted to build something like this, but kudos to Laurent for acutally getting there..

https://www.youtube.com/watch?v=yy4Gr11EXHM

He's got a few videos up of it in action.. Nothing ultra crazy, but proof it's all working..
https://www.youtube.com/channel/UCDfSVxlHK9AJHPRCoGqDYZQ
 
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2019-11-23 23:14
TheRyk

Registered: Mar 2009
Posts: 707
amazing!
2019-11-26 20:00
tlr

Registered: Sep 2003
Posts: 1270
Cool concept! I guess something like this could be done using the 1541U2 as platform. I think there was some experimental copper code in there at one time but you could always go full custom.
2019-11-30 22:06
ciccior2003

Registered: Jun 2012
Posts: 4
I agree with tlr. It would be fantastic if 1541U2 will implement it!!! ;)
2019-12-03 16:02
knue

Registered: Dec 2012
Posts: 32
What kind of sorcery is this? Can someone enlighten me???

My understanding is that an external CPU within the CRT drives the entire machine while the 6510 is idle - correct? Why must it be Ultimax mode and what does DMA mode mean in this context?
2019-12-03 16:28
Golara

Registered: Jan 2018
Posts: 201
Quote: What kind of sorcery is this? Can someone enlighten me???

My understanding is that an external CPU within the CRT drives the entire machine while the 6510 is idle - correct? Why must it be Ultimax mode and what does DMA mode mean in this context?


Yes, 6510 is idle and he's feeding VIC with registers using external CPU. When you have a BADLINE VIC will raise some line which makes the CPU idle, that's when you can inject your own CPU... I think that's how ultimate 1541-II works but don't quote me on that :P Ultimax mode... I know it banks out all the ram, leaving you with 4kb rom image, but I don't know why it's relevant here
2019-12-03 17:12
Krill

Registered: Apr 2002
Posts: 1409
Ultimax mode is the only PLA setting which allows VIC to fetch external data, due to a lot of open memory ranges.
There will be no chip-select signal to any chips on the motherboard for those, so a cartridge can snoop on the address bus and put anything on the data bus for the open addresses, without conflicts.

This is also why you can briefly see a "charset" in RAM at $1000..$1fff or $9000..$9fff (and not the chargen ROM) when freezing with Action Replay or similar catridges, which exploit the Ultimax mode.
2019-12-03 18:47
JackAsser

Registered: Jun 2002
Posts: 1599
Quote: Yes, 6510 is idle and he's feeding VIC with registers using external CPU. When you have a BADLINE VIC will raise some line which makes the CPU idle, that's when you can inject your own CPU... I think that's how ultimate 1541-II works but don't quote me on that :P Ultimax mode... I know it banks out all the ram, leaving you with 4kb rom image, but I don't know why it's relevant here

Ultimax=allow the vic to read external ROM
DMA=put the cpu in idle state
2019-12-03 20:48
knue

Registered: Dec 2012
Posts: 32
ic, thanks :)
2019-12-04 08:05
Martin Piper

Registered: Nov 2007
Posts: 403
And the ROM doesn't have to be a ROM, it can be any signal from any source.
2019-12-04 11:48
Krill

Registered: Apr 2002
Posts: 1409
Quoting Martin Piper
And the ROM doesn't have to be a ROM, it can be any signal from any source.
Thought that as well, but technically, VIC always only reads data (except for RAM refresh). =)

Then again, the CPU may also write to external addresses (if not permanently halted by perpetual DMA).

Anyhow, with VIC reading external data, one could make something that would convert whatever video signal to VIC bitmap/characters (with FLI and sprites and whatnot) at full 50 Hz refresh rate. Kinda lame, but kinda cool as well. View random videos through a realthing VIC filter.
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