tepples wrote:
In other words, claiming that the 68000's inferior IPC is a good thing.
That depends, when it comes to handling large numbers the 68000 is better, and that's a place where a lot of abuse happened (Treasure's complaint about the SNES not being able to pull off things like Alien Soldier probably has something to do with this - also the fact that it was probably easier to program for, saving debugging time). The 68000 is horribly slow when it has to access memory though... You're looking at an average of 12~20 cycles for an opcode with memory access (akin to 6~10 cycles on the 65816 in HiROM).
The 65816 is better at accessing memory instead, especially with regards to zero page (which is practically register-like speed), although it's kind of dumbed down by the opcodes (many opcodes involve the A register, in contrast with the 68000 where if a register is in use you can use any of its kind, and many opcodes allow a lot of different combinations as well), so that may negate its speed somewhat by spending opcodes having to move stuff around. Also that made it harder to program =P
Shiru wrote:
Another interesting thing in this regard is that popular 8-bit Z80 CPU, used in many systems, has 4-bit ALU internally.
So
that is why the Z80 takes 4 cycles minimum... Actually um, I thought it was decode opcode > run opcode > update address low byte > update address high byte?
In any case the Z80 is insanely slow, it suffers from the same issue as the 68000 in terms of cycle usage, but it suffers the same issue as the 65816 for register usage, and it lacks the zero page advantage, so it's basically the worst of both worlds. That's really annoying, especially when you have to push a new sample exactly every 336 cycles (which is the case of my sound engine). There's some error margin before the human ear can notice it, but not much and it's still annoying. Glad the hardware timers loop on their own, even if I have to still poll them manually (as there are no interrupts)...
I guess this is going off-topic anyway so I better stop here.