Free DMA implementation on 6502s ?

[andym00]

Came across this when looking through the MOS Wiki entry...

 

http://homepage.mac.com/jorgechamorro/a2th...agic/index.html

 

Is this actually feasible ? Reading it seems to make sense to me, and the amount of memory it could potentially shift seems not to be sniffed at..

Clearly it's a bit late for it to be of any practical use on systems, but I'm just curious if this is viable, and if so, why it was never implemented back in the days or even used in some 6502 variant as some built in background-DMA device..

 

Just curious

[Rybags]

Atari's don't have this "Sync" line on their 6502.

 

Maybe the old 400/800 did (but I doubt it), the Sally in later machines doesn't for sure.

[ijor]

Atari's don't have this "Sync" line on their 6502.Maybe the old 400/800 did (but I doubt it), the Sally in later machines doesn't for sure.

 

I'm not sure what you meant Rybags, SALLY does have a SYNC signal, and of course that the standard 6502 on the 400/800 has it as well.

 

Yet, ANTIC DMA and RAM Refresh makes this idea pretty difficult to implement.