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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 timing log -- solo append, mai troncato/sovrascritto (vedi README.md)
# Nessuna entry ancora -- popolato incrementalmente man mano che avanza lo sviluppo V2.
[2026-09-05] EXP-0001 -- neural_processor (P_IN=8, ACC_WIDTH=32)
nextpnr-ecp5 --45k --package CABGA381 --speed 8 --freq 80
--lpf-allow-unconstrained
Fmax: 183.12 MHz -- PASS at 80 MHz (real place&route measurement)
Critical path: job_ready -> TRELLIS_IO output pad (i.e. the design's
own logic is NOT the bottleneck at this Fmax -- an unconstrained
output pin dominates; a real system-level Fmax will differ once
this signal is consumed on-chip instead of driven to a pad in
isolation). Log: hardware/v2/synthesis/neural_processor_p8/nextpnr.log
WNS/TNS: not reported by this nextpnr version in this invocation.
[2026-09-05] EXP-0002 -- neural_processor (P_IN=8, ACC_WIDTH=24)
Same command as above, ACC_WIDTH=24 build.
Fmax: 176.21 MHz -- PASS at 80 MHz (real place&route measurement)
Delta vs ACC_WIDTH=32: -6.91 MHz (-3.8%) despite FEWER resources --
attributed to placement noise, not a real architectural effect
(no seed sweep run to confirm either way -- see experiments.log
EXP-0002 and benchmark.log). Log: hardware/v2/synthesis/
neural_processor_p8_acc24/nextpnr.log
[2026-09-05] EXP-0003 -- N_PROCESSORS sweep (P_IN=8), real nextpnr-ecp5
--45k --package CABGA381 --speed 8 --freq 80 --lpf-allow-unconstrained
N=1: Fmax=159.11 MHz PASS MULT18X18D 8/72 (11%)
N=2: Fmax=149.59 MHz PASS MULT18X18D 16/72 (22%)
N=4: Fmax=151.01 MHz PASS MULT18X18D 32/72 (44%)
N=8: Fmax=134.70 MHz PASS MULT18X18D 64/72 (88%)
TRELLIS_IO stays at 18/245 (7%) throughout (harness has only
clk/rst/seed/checksum as real pins, by design -- see ERR-0005).
See decisions.log DEC-0005: DSP, not Fmax or LUT/FF, is the resource
that will first prevent scaling N_PROCESSORS further at P_IN=8.
[2026-09-05] EXP-0004 -- default-depth buffer configs, real nextpnr-ecp5
activation_buffer (D=4096): Fmax=325.20 MHz PASS
weight_buffer (D=512): Fmax=339.67 MHz PASS
result_buffer (D=4096): Fmax=325.20 MHz PASS
All far above the 80MHz target -- buffers are not a timing concern in
isolation at these depths.
[2026-09-05] EXP-0005 -- memory_manager + prefetch_engine (via
harness_memory_manager.v, see errors.log ERR-0005 for why a harness
was needed), real nextpnr-ecp5 --45k --package CABGA381 --speed 8
--freq 80 --lpf-allow-unconstrained
Fmax: 165.86 MHz -- PASS at 80MHz (real place&route measurement)
[2026-09-05] EXP-0006 -- neural_director (via harness_neural_director.v,
see errors.log ERR-0005 for why), real nextpnr-ecp5 --45k --package
CABGA381 --speed 8 --freq 80 --lpf-allow-unconstrained
Fmax: 250.50 MHz -- PASS at 80MHz (real place&route measurement)