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prod: promote EXP-0056 fixes into production RTL (dependency_manager.v, nms_activation_fill_ctrl_v3.v)

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Per explicit instruction: when a bug/fix found in an experimental fork
also applies to the production file it was forked from, apply it
there too, not just in the fork.

dependency_manager.v: swaps in priority_encoder_lsb.v for the
first_ready_idx scan (was: serial O(N_NODES) for-loop). Bit-exact
equivalent, correctness-neutral by construction.

nms_activation_fill_ctrl_v3.v: adds the missing N_SLOTS==16 balanced
max-tree case (was: silently falling back to the slow flat scan for
any N_SLOTS not in {1,2,4,8}) -- this was the real cause of N_SLOTS=16
failing timing closure (23-24MHz vs 64MHz target), fixed to 71.01MHz
PASS in the experimental fork.

Verified on the REAL, unmodified production top (fpga_neural_v2_top.v,
N_SLOTS=4 default): tb_dependency_manager.v 4/4 PASS, board smoke test
11/11 PASS, D-Stress N=4 total_cycles=49927 (bit-exact, IDENTICAL to
the pre-fix baseline -- zero functional regression, as expected from a
pure combinational-depth change). Real nextpnr-ecp5 P&R (LFE5U-45F,
seed 1): 97.36MHz, PASS at 64MHz -- BETTER margin than the pre-fix
baseline's own 76.80-88.25MHz seed range, not just neutral.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MUG92aM9m68TRc4rG55BcC
This commit is contained in:
michele
2026-09-16 12:29:52 +02:00
co-authored by Claude Sonnet 5
parent 49b25f6eb6
commit ca94083366
2 changed files with 59 additions and 14 deletions
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hardware/v2/nms/rtl/nms_activation_fill_ctrl_v3.v
+30
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@@ -178,6 +178,36 @@ module nms_activation_fill_ctrl_v3 #(
if (rst) max_n_tiles_reg <= 16'h0;
else max_n_tiles_reg <= max_final;
end
end else if (N_SLOTS == 16) begin : GEN_MAXTREE_N16
// EXP-0056: same balanced-tree pattern as N_SLOTS==8 above,
// one more level. Promoted from nms_activation_fill_ctrl_v3_n16.v
// (experimental fork) after that fork's own fix was
// verified (isolated: 10017/10017; real nextpnr-ecp5 P&R
// at N_SLOTS=16, LFE5U-85F: 71.01MHz, PASS at 64MHz, vs
// 23.52-24.64MHz before -- see experiments.log EXP-0056)
// -- this exact case used to fall through to
// GEN_MAXTREE_FALLBACK's own flat sequential scan, the
// real measured critical path blocking N_SLOTS=16 timing
// closure.
wire [15:0] m0 = (n_tiles_masked[0] > n_tiles_masked[1]) ? n_tiles_masked[0] : n_tiles_masked[1];
wire [15:0] m1 = (n_tiles_masked[2] > n_tiles_masked[3]) ? n_tiles_masked[2] : n_tiles_masked[3];
wire [15:0] m2 = (n_tiles_masked[4] > n_tiles_masked[5]) ? n_tiles_masked[4] : n_tiles_masked[5];
wire [15:0] m3 = (n_tiles_masked[6] > n_tiles_masked[7]) ? n_tiles_masked[6] : n_tiles_masked[7];
wire [15:0] m4 = (n_tiles_masked[8] > n_tiles_masked[9]) ? n_tiles_masked[8] : n_tiles_masked[9];
wire [15:0] m5 = (n_tiles_masked[10] > n_tiles_masked[11]) ? n_tiles_masked[10] : n_tiles_masked[11];
wire [15:0] m6 = (n_tiles_masked[12] > n_tiles_masked[13]) ? n_tiles_masked[12] : n_tiles_masked[13];
wire [15:0] m7 = (n_tiles_masked[14] > n_tiles_masked[15]) ? n_tiles_masked[14] : n_tiles_masked[15];
wire [15:0] m01 = (m0 > m1) ? m0 : m1;
wire [15:0] m23 = (m2 > m3) ? m2 : m3;
wire [15:0] m45 = (m4 > m5) ? m4 : m5;
wire [15:0] m67 = (m6 > m7) ? m6 : m7;
wire [15:0] m0123 = (m01 > m23) ? m01 : m23;
wire [15:0] m4567 = (m45 > m67) ? m45 : m67;
wire [15:0] max_final = (m0123 > m4567) ? m0123 : m4567;
always @(posedge clk) begin
if (rst) max_n_tiles_reg <= 16'h0;
else max_n_tiles_reg <= max_final;
end
end else begin : GEN_MAXTREE_FALLBACK
reg [15:0] max_n_tiles_comb_fallback;
integer j;