Final milestone of docs/v2-description.md's §33 roadmap, scoped
exactly to its own mandate: optimize only on data already gathered in
M1-M9, across the pipeline/P_IN/processor-count/scheduling/memory
axes - no speculative new features.
Three concrete, data-driven results:
1. N_SLOTS=8 (numero processor axis): real synthesis + nextpnr-ecp5
P&R for dataflow_core at N_SLOTS=8, extending M7's N_SLOTS=2/4
sweep to the real DSP ceiling DEC-0005 predicted. 92.63 MHz
POST-P&R, PASS at 80MHz, DSP 64/72 (88.9%). DEC-0012 recommends
N_SLOTS=8 as the practical ceiling for P_IN=8 on the
LFE5U-45F-8BG381.
2. ACC_WIDTH 24 vs 32 (pipeline axis): a real 6-seed nextpnr-ecp5
placement sweep (reusing already-synthesized netlists, no new
synthesis needed) resolves EXP-0002's single-seed
inconclusiveness. ACC_WIDTH=24 wins on both mean Fmax (+6.2%,
180.71 vs 170.12 MHz) and seed-to-seed variance (~3.4x tighter),
on top of its already-known resource advantage. DEC-0013
recommends ACC_WIDTH=24 as the new default.
3. Stall %/utilization (scheduling/memory axes): testbench-only cycle
counters added to tb_neural_multiprocessor.v (no RTL touched)
close DEC-0011's deferred measurement gap with real data - shared
PSRAM port 81.7% utilized, slot 0 95.2%, slot 1 65.2%, no
conclusive evidence of harmful fixed-priority starvation at this
scale.
The 10-milestone V2 roadmap (docs/v2-description.md §33) is now
complete end-to-end: real Verilator simulation, real Yosys synthesis,
real nextpnr-ecp5 place & route for every milestone, fully logged
(EXP-0001..EXP-0013, DEC-0001..DEC-0013, ERR-0001..ERR-0008) with no
invented results (§30) and V1 kept frozen and untouched throughout
(§1/§34).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
neural_multiprocessor.v wraps dataflow_core.v (M7, unmodified) around
the real, unmodified V1 PSRAM backend chain (int8_memory_access ->
memory_interface -> psram_controller), funneling N_SLOTS independent
Memory Backend Interface ports through a new generic N-port arbiter
(slot_mem_arbiter.v) inspired by (not copied from) V1's own
mem_arbiter.v.
Real concurrent-slot simulation immediately surfaced a genuine bug
(ERR-0008): memory_manager/prefetch_engine's byte-level backend
protocol is fire-and-forget (a single-cycle mem_req pulse with no
accept handshake) - correct for M4's direct 1:1 connection, but a
naive arbiter silently drops a pulse arriving while the shared bus is
owned by another slot, hanging that slot forever. Fixed with a
per-port pending-request latch, the same "queue, don't drop" idiom
already used by memory_manager's own pf_pending register (ERR-0006).
Verified (Verilator): 4/4 PASS with 2 slots genuinely contending for
one real PSRAM port (444 cycles). No regression on M4's own
testbench. Real synthesis + nextpnr-ecp5 P&R (no harness needed - real
PSRAM pins keep the top-level at 157 pins): 0 problems, Fmax 142.45
MHz, PASS at 80MHz.
Arbitration policy is fixed lowest-index priority, not fairness-
balanced (DEC-0010) - consistent with every other "simplest correct
policy first" scheduling choice in this roadmap, revisited only if
M9's real measurement shows starvation matters.
Logged: simulation/synthesis/timing/benchmark/decisions (DEC-0010)/
experiments (EXP-0009)/errors (ERR-0008)/development.log, ROADMAP.md
updated.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
micheleandClaude Sonnet 5