How feasible is it to use the REU (well mainly it's 8726) as a rough Blitter ? Would there be much advantage to it over the CPU ? Useful for demos/games ?
Just a thought that popped into my head asking to be asked :-)
Mark
Well, there were some plans to use the REU to shuffle the graphics around in Pinball Dreams 64. That later change to linecrunching (and thus smaller playfield) as few people have REU's. I played around a little with such a routine myself, and used the REU RAM to store and scroll a really large image :)
The REU was also used in a demo (http://noname.c64.org/csdb/release/?id=7446) to change the background color in each cycle, thus creating a nice effect in the border.
Here's what it says in some file I got somewhere on the Intertubes (sorry, I don't remember where):
"One other application (used in GEOS) is to copy C64 RAM areas
by first transferring it to the REU and then transferring it back into
the desired position in C64 memory. Due to the fast DMA this is about 5
times faster than copying memory with machine language instructions...
... It would be possible to use real bitmap graphics in the upper and lower
screen border by changing the "magic byte" (highest by the VIC addressed
byte) in every clock cycle during the border switched off.
Generally the REC could be used as graphics accelerator e.g. to
copy bitmap areas or to copy data fast into the VIC-addressable
16 KByte area."