I'd sure like to look at that source...
(I booted twc9 smp linux on it many, many, many times during my brief
time at SiCortex;
it worked great!)
-brad
Bob Supnik wrote:
I solved this problem when I used SIMH as the foundation for a
simulator of the SiCortex 6-core system on a chip. I never published
that work while the company was in business, and now that it has
folded, I didn't think it was interesting anymore.
I have permission from the inheritors of the IP to publish the
simulator, unsupported, if people want to look at the techniques it
used. It was compiled against SIMH 3.8-0 and added many
system-specific features, so I don't think it will work against the
current distribution; it may not work on any environment except 64b
Linux, in fact. It does have quite a reasonable MIPS64 emulator,
complete with floating point, which people might like.
The SMP model is an extension of the multi-controller techniques used
in the PDP11 RQ simulator. There is a global shared memory and IO
subsystem, and then all processor state is encapsulated in a large
structure, the context. The CPU is no longer in charge; instead, it
provides a routine, cpu_one_inst, that is called multiple times from
the master controller (placed in the MEMory controller, for convenience):
while (reason == 0) { /* loop until
halted */
if (sim_interval <= 0) { /* check clock
queue */
if ((reason = sim_process_event ())) break;
eval_intr_all ();
}
sim_interval = sim_interval - 1;
reason = cpu_one_inst (cpu_ctx[0]);
for (i = 1/*not0*/; i < NUM_CORES; i++) {
if (cpu_enb[i] && (r1 = cpu_one_inst (cpu_ctx[i])))
reason = cpu_report_err (reason, r1, dev_list[i],
cpu_ctx[i]);
}
} /* end while */
So all the cores execute in lockstep on a round robin basis; one
simulator cycle includes executing one instruction for all enabled
cores. The simulator also included mechanisms for detecting when the
cores were idle and skipping them.
Heterogeneous multiprocessing can be implemented the same way, except
that memory is local to each CPU, not global; and IO is not shared but
distributed among the CPUs.
When we were implementing HP Access 2000 (linked processors), I looked
at rewriting the HP CPU and IO system to this model but concluded it
was too much trouble. So Access runs separate simulator images that
communicate over sockets - inefficient but workable.
/Bob Supnik
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