Multithreaded execution on Spike

[sberkun]

Currently, single-threaded execution on spike works with https://github.com/lf-lang/lingua-franca/tree/baremetal_spike_support and https://github.com/lf-lang/reactor-c/tree/baremetal_spike_support. However, there is no existing support for multi-threaded execution.

Spike can simulate multiple threads with -p flag (i.e. spike --isa=rv32i -p4 demo.riscv), so it would be great if we could take advantage of that.

This will most likely involve modification of the files in the core/spike/common folder, particularly crt.S. Right now, crt.S contains the following lines:

  # get core id
  csrr a0, mhartid
  # for now, assume only 1 core
  li a1, 1
1:bgeu a0, a1, 1b

  # give each core 128KB of stack + TLS
#define STKSHIFT 17
  add sp, a0, 1
  sll sp, sp, STKSHIFT
  add sp, sp, tp
  sll a2, a0, STKSHIFT
  add tp, tp, a2

  j _init

Supporting multiple threads will involve removing the assumption of only 1 core, and then figuring out what to do with the other cores.