HMM trellis microkernel (hmm_step.c)

  • Location: smile/progs/sci/hmm_step.c
  • Workload: Viterbi-style forward trellis for a 3-mer HMM
    • M = 64 states, N = 26 events, NUM_PATH = 21 transitions/state
  • Result:
    • Computes a checksum over the final column + end-state
    • Stores it at 0x0100 and exits with code result & 0xff
# A manual and basic run of the HMM kernel.
smarc $ cd smile/progs
smarc/smile/progs $ riscv64-unknown-elf-gcc -Os -march=rv32i_zicsr -mabi=ilp32 -ffreestanding -nostdlib -nostartfiles -Wl,-T link_rv32.ld -Wl,-e,_start -Wl,--no-relax sci/hmm_step.c -o prog.elf
smarc/smile/progs $ riscv64-unknown-elf-objcopy -O binary prog.elf prog.bin
smarc/smile/progs $ cd ../..
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/prog.bin -load_addr=0x0 -start_pc=0x0 -steps=2000000

You should see something like

[EXIT] Program exited with code 253
[STATS] inst=1819089 loads=291812 stores=147534 branches=261794 taken=228708

There are some alternative ways to get this run. First you can create the binary much more easily by building the hmm_step target in CMake:

# This makes smile/progs/hmm_step.bin for you (among other things)
smarc $ cmake --build build --target smile_progs -j

You can run the compiled program in ideal mode.

# 1) Default run (timed mode, default mem latency)
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -steps=20000000
[EXIT] Program exited with code 253
[EXIT] Program exited with code 253
[STATS] cycles=2066108 inst=924030 alu=568503 add=228239 mul=0 loads=144306 stores=73742 branches=120885 taken=109879

Expected:

  • Program exits cleanly with code 253.
  • You should see [EXIT] Program exited with code 253.
  • inst, loads, stores, and branches are deterministic for a fixed binary.
# 2) Explicit ideal mode (boolean flag)
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -steps=20000000 -ideal_mem=true
[EXIT] Program exited with code 253
[EXIT] Program exited with code 253
[STATS] cycles=924030 inst=924030 alu=568503 add=228239 mul=0 loads=144306 stores=73742 branches=120885 taken=109879

# 3) Explicit ideal mode (string flag; equivalent to -ideal_mem=true)
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -steps=20000000 -mem_model=ideal
[EXIT] Program exited with code 253
[EXIT] Program exited with code 253
[STATS] cycles=924030 inst=924030 alu=568503 add=228239 mul=0 loads=144306 stores=73742 branches=120885 taken=109879

Expected for both ideal runs:

  • Same functional result as timed mode (exit code 253).
  • Same instruction mix counters (inst/loads/stores/branches) as timed mode.
  • Lower cycle count when memory latency is non-zero.
# 4) Timed vs ideal comparison at non-zero latency
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -mem_latency=3 -steps=20000000 -mem_model=timed
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -mem_latency=3 -steps=20000000 -mem_model=ideal

Expected (reference numbers from this repo as of Feb 2026):

# timed, mem_latency=3
[EXIT] Program exited with code 253
[STATS] cycles=4350264 inst=924030 alu=568503 add=228239 mul=0 loads=144306 stores=73742 branches=120885 taken=109879

# ideal, mem_latency=3
[EXIT] Program exited with code 253
[STATS] cycles=924030 inst=924030 alu=568503 add=228239 mul=0 loads=144306 stores=73742 branches=120885 taken=109879

# 5) Optional trace-heavy run for debugging
smarc $ ./build/smile/tb_tile1 -prog=smile/progs/hmm_step.bin -load_addr=0x0 -start_pc=0x0 -ignore_bpfile=1 -mem_latency=3 -steps=200 -trace "Tile1"

Expected:

  • Per-cycle instruction trace lines from Tile1.
  • Useful for spot-checking fetch/decode/PC flow; not recommended for full kernel runs due to log volume.

For a chronological list of runs and stats, see hmm_step experiment log.