All,
Very good discussion. I will look at MESS.
I think Holger hit the nail on the head. I can emulate functionality at
the multibus interface and use the SIMH queue to do the work much as the
AltairZ80 did at the S-100 interface. Threads would possibly break the
portability of SIMH and I don't want to do that.
Back to think on this problem while I get the 8088/8086/8188/80186/80286
processor emulation completed and validated.
Bill
On 04/05/2011 05:00 AM, Holger Veit wrote:
Am 04.04.2011 23:53, schrieb Rob Jarratt:
Threads in SIMH would be great for emulating many devices too. I
suspect the
reason they are not there and that it is polled is portability. I
have never
looked into seeing if there is a way to get threads on all the supported
platforms, but if anyone else has then it would be interesting to
hear about
it.
Regards
Rob
On 04/04/11 5:10 PM, Bill Beech (NJ7P) wrote:
All,
I am in the process of writing an emulator for the Intel 310 system.
I would like to know if anyone has figured a way to emulate multiple
processors in one emulation? The Intel 310 used the following
processors simultaneously:
Master CPU 80286
Serial Board Slave 80188
Ethernet Slave 80188
Tape Drive Slave 8089
Hard Disk Slave 8089
Any thoughts?
You don't need threading in simh, because it already implements sort
of threads by
implementing an event queue to process I/O events. Threads are just a
light-weight
word for "scheduling in a single executable". Simh is thus very
similar to an operating system
(as any simulator is, in principle).
What you need for multiprocessors is splitting the sim_instr()
function into independent
handlers for each CPU. When done correctly, it will also allow
multiple instances of
the same CPU in a single simulator.
Admittedly, doing this is much simpler with real OO concepts, where
you just instantiate
one or more CPU classes and then, in a loop call their "sim_instr"
methods sucessively
for a single CPU instruction and increment simulator time accordingly.
Besides, many simulators have "intelligent" I/O gear; you should
carefully analyze whether
the tape and disk slave subsystems actually need to be emulated
precisely, or just at their
I/O border to the main CPU. See the Altair simulator in simh, for
instance: the built-in floppy disk
controller, including a DMA controller, might have been simulated
precisely as if it were an independent
machine, but actually, it is sufficient to pass it certain
read/write/format/seek commands in
special registers, and then, after some time passed, it will magically
transfer data from an emulated
disk file directly to the emulated main memory of the Altair machine,
and throws a "command done"
interrupt.
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