22 Apr
2024
22 Apr
'24
11:46 a.m.
On Apr 22, 2024, at 2:34 PM, Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> wrote:
On 4/22/24 11:09, Bill Gunshannon via cctalk wrote:
Probably not. Cycle accurate simulation is very hard. It's only rarely been done for
any CPU, and if done it tends to be incredibly slow. I remember once using a MIPS
cycle-accurate simulator (for the SB-1, the core inside the SB-1250, later called
BCM-12500). It was needed because the L2 cache flush code could not be debugged any other
way, but it was very slow indeed. Almost as bad as running the CPU logic model in a
Verilog or VHDL simulator. I don't remember the numbers but it probably was only a
few thousand instructions per second.
Then again, for the notion of a drop-in replacement for the original chip, you don't
need a cycle accurate simulator, just one with compatible pin signalling. That's not
nearly so hard -- though still harder than a SIMH style ISA simulation.
paul
Following along this line of thought but also in regards all our
other small CPUs....
Would it not be possible to use something like a Blue Pill to make
a small board (small enough to actually fit in the CPU socket) that
emulated these old CPUs? Definitely enough horse power just wondered
if there was enough room for the microcode.
Blue pills are so yesterday! There are far more small-footprint MCUs
out there. More RAM than any Z80 ever had as well as lots of flash for
the code as well as pipelined 32-bit execution at eye-watering (relative
to the Z80) speeds.
Could it emulate a Z80? I don't see any insurmountable obstacles to
that. Could it be cycle- and timing- accurate? That's a harder one to
predict, but probably.