> > > Which takes me back about two weeks when someone suggested that the > > PC wasn't powerful enough to emulate the SAM - well, if it can > > emulate a C64 with its complicated screen modes and SID chip > > then it can certainly emulate the SAM. > > I don't recall that the C64 had particularly complicated > screen modes (were there more than two?), but it had a funny > way of handeling it which made it virtually impossible to draw > bitmaps with the 1MHz processor. In stead it heavily relied on > sprites, which we all know is not very tricky.
The C64 has three text modes (standard, multicolour and extended colour) two bitmap modes (spectrum-style and multicolour), sprites (mono or multicolour), horizontal & vertical hardware scrolling, and just about any combination of these using raster interrupts. I'm not sure what you mean by sprites are not very tricky - do you mean not tricky to use (I agree), to emulate (not sure..) or to implement in hardware (I definitely disagree!). Also, comparing the 1MHz 6502 clock to the 3.25 of the Spec or 6 of the SAM is a bit dodgy since z80s take 4 cycles to read from memory, one more for I/O, whereas the 6502 only takes 1. Also, many 6502 instructions execture in 2 cycles, some take 1, some take 3. > > The thing about the SAM that makes it so darn difficult, is > that you can actually DO things at the end of each scan-line, > like changing screen-modes, select another screen to be displayed, > change palette, etc. The mere task of keeping the timing of each > line-interrupt will take a LOT of time, not to speak about how > to actually switch screen, modes etc. on the fly. This is all in the > SAMs hardware. Not even Z80 manages to emulate the (ab)use of > the second screen on 128K 100%. It's all in the C64 hardware too.... -AG
