feat(rtl): migrate CAM interface to handshake protocol with integrated noise generation

BREAKING CHANGE: CAM write and query interface replaced with standard valid/ready
handshake. wr_en/wr_row/wr_hash → wr_valid/wr_ready/wr_addr/write_hash.
External noise_mask_lanes_flat removed; noise generation now handled internally
by cam_noisy module with configurable rate via parameters.

- cam_top: add parameters (NOISE_EN, NOISE_RATE_NUM/DEN, NOISE_GEN/SAMPLE_BITS, NOISE_SEED)
- cam_top: replace cam_core with cam_noisy (integrated noise generation)
- match_engine: remove external noise_mask_lanes_flat input
- hw/sim: update Makefile with noise parameters and compile args
- hw/sim/model: add generate_write_flip_mask() and xorshift64() matching RTL behavior
- hw/sim/tests: adapt testbench to new handshake protocol

hw/sim/sweep_noise.py

@@ -1,9 +1,41 @@
+"""Sweep write-noise rates and measure top-1 stability.
+
+Applies write-noise flip masks to stored rows (simulating noisy writes),
+then queries the noisy rows and compares top-1 results against clean rows.
+"""
+
 from __future__ import annotations
 
 import argparse
 
 import numpy as np
-from model.ref_model import match_top1, random_hashes, random_noise_masks
+from model.ref_model import (
+    generate_write_flip_mask,
+    match_top1,
+    random_hashes,
+)
+
+
+def apply_write_noise(
+    rows: list[int],
+    *,
+    width: int,
+    rate_num: int,
+    rate_den: int,
+    noise_gen_bits: int = 8,
+    noise_sample_bits: int = 8,
+    seed: int = 0,
+) -> list[int]:
+    """Apply write-noise flip masks to every row, returning noisy copies."""
+    noisy: list[int] = []
+    state = seed
+    mask_w = (1 << width) - 1
+    for row in rows:
+        flip, state = generate_write_flip_mask(
+            state, width, noise_gen_bits, noise_sample_bits, rate_num, rate_den
+        )
+        noisy.append((row ^ flip) & mask_w)
+    return noisy
 
 
 def main() -> None:
@@ -12,6 +44,8 @@ def main() -> None:
     parser.add_argument("--queries", type=int, default=128)
     parser.add_argument("--width", type=int, default=512)
     parser.add_argument("--seed", type=int, default=1234)
+    parser.add_argument("--noise-gen-bits", type=int, default=8)
+    parser.add_argument("--noise-sample-bits", type=int, default=8)
     parser.add_argument(
         "--rates",
         type=float,
@@ -29,19 +63,30 @@ def main() -> None:
 
     clean_results = [match_top1(q, rows, width=args.width) for q in queries]
 
-    print("rate,top1_stability,avg_clean_margin")
+    # Use a fixed denominator matching the 8-bit sample space (2^8 = 256).
+    # Note: floor() is used, matching RTL threshold = (rate_num * 256) // rate_den.
+    # Rates below 1/256 (≈0.39%) collapse to zero under this scheme.
+    rate_den = 256
+
+    print("rate,rate_num,effective_prob,top1_stability,avg_clean_margin")
     for rate in args.rates:
+        rate_num = int(rate * rate_den)
+        effective = rate_num / rate_den if rate_den > 0 else 0.0
         stable = 0
         margins = []
 
+        noisy_rows = apply_write_noise(
+            rows,
+            width=args.width,
+            rate_num=rate_num,
+            rate_den=rate_den,
+            noise_gen_bits=args.noise_gen_bits,
+            noise_sample_bits=args.noise_sample_bits,
+            seed=args.seed,
+        )
+
         for q, clean in zip(queries, clean_results):
-            noise_masks = random_noise_masks(
-                rng,
-                args.rows,
-                width=args.width,
-                bit_flip_rate=rate,
-            )
-            noisy = match_top1(q, rows, width=args.width, noise_masks=noise_masks)
+            noisy = match_top1(q, noisy_rows, width=args.width)
 
             if noisy.top1_index == clean.top1_index:
                 stable += 1
@@ -50,7 +95,7 @@ def main() -> None:
             margin = int(sorted_scores[-1] - sorted_scores[-2])
             margins.append(margin)
 
-        print(f"{rate},{stable / args.queries:.6f},{np.mean(margins):.3f}")
+        print(f"{rate},{rate_num},{effective:.6f},{stable / args.queries:.6f},{np.mean(margins):.3f}")
 
 
 if __name__ == "__main__":