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micheleandClaude Sonnet 5 2e4cedc761 feat(v2): M5 Neural Director, first-free job scheduling
Implements M5: neural_director.v dispatches job descriptors to
whichever of N_SLOTS (memory_manager, neural_processor) pairs is
currently free (first-free scheduling per §9's initial policy), with
a parametric-depth ready-queue FIFO for jobs arriving faster than
slots can absorb them.

Scope for this milestone (see decisions.log DEC-0007): a reduced
4-state FSM (DIR_IDLE/SCAN_READY/ALLOCATE/ERROR) rather than §9's full
8-state baseline -- dependency tracking, the waiting queue, and
wake-up are §10's explicit responsibility (Dependency Manager, M6, not
yet built), and slot-completion detection runs as an always-active
per-slot tracker rather than a dedicated FSM state, for the same
reason DEC-0002 already gave for the Neural Processor's own FSM
(gating concurrent per-unit progress behind one shared state kills
throughput).

Verified with Verilator (N_SLOTS=2, each slot backed by its own
independent behavioral memory rather than sharing V1's real PSRAM --
M4 already proved that path for one slot; this milestone's own concern
is scheduling across multiple slots): 4/4 tests pass -- 3 jobs
submitted to 2 slots (first two dispatch immediately, third correctly
queues until a slot frees), and a deliberate burst that forces the
ready queue to genuinely fill and recover.

Real synthesis: 0 CHECK problems, 382 LUT4/366 FF/4 CCU2C/0 DSP. Real
place&route (via a synthesis-only timing harness, same TRELLIS_IO
pin-budget reason as M2/M4): Fmax 250.50 MHz, PASS at 80MHz.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
2026-09-05 14:46:32 +02:00

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# V2 benchmark log -- solo append, mai troncato/sovrascritto (vedi README.md)
# Nessuna entry ancora -- popolato incrementalmente man mano che avanza lo sviluppo V2.
[2026-09-05] M1 single Neural Processor, isolated (no array/director/
memory manager yet -- system-level numbers deferred to M9)
| Config | Fmax (POST-P&R) | LUT | FF | DSP | BRAM |
|----------------------|------------------|-----|-----|-----|------|
| P_IN=8, ACC_WIDTH=32 | 183.12 MHz | 55 | 533 | 8 | 0 |
| P_IN=8, ACC_WIDTH=24 | 176.21 MHz | 49 | 509 | 8 | 0 |
Reference (V1, hardware/v1/synthesis/p8/, isolated neuron_parallel,
PARALLEL=8, N_INPUTS=256): 61.71 MHz POST-P&R.
All Fmax figures above are POST-P&R (real nextpnr-ecp5), not
theoretical or simulated-only. MAC/cycle, cycles/neuron, neurons/s,
stall %, effective MAC/s: not yet meaningful at this milestone (single
isolated processor, no streaming benchmark harness yet -- deferred to
M2 once neural_processor_array.v exists and a real workload can be
timed end-to-end).
[2026-09-05] M2 Neural Processor Array, N_PROCESSORS sweep (P_IN=8,
ACC_WIDTH=32 each; synthesized via the timing harness, see errors.log
ERR-0005 for why)
| N_PROCESSORS | Fmax (POST-P&R) | LUT | FF | DSP (MULT18X18D) | DSP % of 72 |
|--------------|------------------|-----|------|-------------------|-------------|
| 1 | 159.11 MHz | 59 | 409 | 8 | 11% |
| 2 | 149.59 MHz | 106 | 786 | 16 | 22% |
| 4 | 151.01 MHz | 207 | 1540 | 32 | 44% |
| 8 | 134.70 MHz | 374 | 3048 | 64 | 88% |
All figures POST-P&R (real nextpnr-ecp5), all PASS at the 80MHz
target. LUT4 utilization stays under 6% of the device even at N=8;
DSP is the binding resource (see decisions.log DEC-0005), reaching 88%
at N=8 -- N_PROCESSORS=9 would already exceed the LFE5U-45F's 72
MULT18X18D budget at P_IN=8. Theoretical MAC/cycle (THEORETICAL, not
yet measured end-to-end -- no real workload/benchmark harness exists
until M9): N_PROCESSORS * P_IN MACs/cycle when all processors are
simultaneously streaming tiles (8, 16, 32, 64 for N=1/2/4/8 -- verified
achievable in principle by EXP-0003's concurrent/staggered simulation,
not yet measured as a sustained throughput number).
[2026-09-05] M3 buffers -- BRAM cost vs DEPTH (real Yosys synth_ecp5)
| Module | DEPTH | DP16KD | LUT4 | FF |
|--------------------|-------|--------|------|-----|
| activation_buffer | 4096 | 2 | 37 | 30 |
| activation_buffer | 256 | 1 | 21 | 26 |
| weight_buffer | 512 | 2 | 88 | 139 |
| weight_buffer | 64 | 2 | 73 | 136 |
| result_buffer | 4096 | 2 | 37 | 30 |
| result_buffer | 256 | 1 | 21 | 26 |
weight_buffer's DP16KD count is flat across an 8x depth reduction --
its 64-bit TILE_WIDTH (P_IN=8 * DATA_WIDTH=8), not DEPTH, determines
BRAM count for this module. activation_buffer/result_buffer (byte-
wide) scale as expected with depth. Confirms §14's warning literally:
"non assumere che buffer piu' grandi siano automaticamente migliori"
-- here, smaller was not cheaper either, because depth was the wrong
lever for this specific buffer's cost.
[2026-09-05] M4 Memory Manager + Prefetch Engine (standalone resource
count; Fmax via timing harness -- see errors.log ERR-0005)
| Module | Fmax (POST-P&R) | LUT | FF | DSP | CCU2C |
|----------------------------------|------------------|-----|-----|-----|-------|
| memory_manager + prefetch_engine | 165.86 MHz | 851 | 789 | 0 | 108 |
End-to-end (real PSRAM + real neural_processor, SIMULATED only, no
system-level P&R yet -- deferred to M7/M9): 3-tile job = 446 cycles,
1-tile job = 166 cycles, 5-tile job = 728 cycles. ~140-150 cycles/tile,
dominated by psram_model.v's real ~70ns TAA access latency, not by
memory_manager's own control overhead (its bank-swap turnaround is
documented as a fixed +1 cycle/tile in decisions.log DEC-0006, a small
fraction of the ~140-cycle PSRAM-dominated total).
[2026-09-05] M5 Neural Director (standalone resource count; Fmax via
timing harness -- see errors.log ERR-0005)
| Module | Fmax (POST-P&R) | LUT | FF | DSP | CCU2C |
|------------------|------------------|-----|-----|-----|-------|
| neural_director (N_SLOTS=4) | 250.50 MHz | 382 | 366 | 0 | 4 |