refactor(cam): remove read noise from noise architecture (Phase 2)

- Make cam_read_noise a pass-through module, removing all noise injection logic
- Switch write noise to use noise_mask_bernoulli instead of noise_mask_grouped
- Add state machine to cam_write_noise for mask generation timing
- Remove noise_mask_grouped.sv (no longer needed)
- Remove read noise parameters from cam_noisy and cam_top
- Update simulation and benchmark code to reflect read noise removal
- Sync documentation to reflect Phase 2 architecture

hw/sim/tests/top/read_noise/test_read_noise.py

@@ -1,27 +1,9 @@
 # -*- coding: utf-8 -*-
 """
-CAM 读取噪声（read_noise）集成测试。
+CAM 读取路径 pass-through 集成测试 — Phase 2 cleaned.
 
-本文件针对 READ_NOISE_EN=1 的编译配置，验证 RTL 的读取噪声行为
-与 Python 参考模型（ref_model）一致。
-
-=== 测试内容 ===
-
-  read_noise_model_match — 读取噪声模型匹配：
-    写入原始哈希，预测含写入噪声（如果 WRITE_NOISE_EN=1）的存储值，
-    再用 match_top1_with_read_noise 计算含读取噪声的期望结果，
-    与 RTL 实际 Top-1 进行比对。
-
-=== 架构背景 ===
-
-  CAM 硬件由以下流水线组成：
-    Write Noise → Banked Core Storage → Read Noise → Match Engine Pipeline
-                                                     ↓
-                                               Top-K Tracker → Result Serializer
-
-  本测试覆盖的是 Read Noise → Match Engine 段。
-  写入噪声（WRITE_NOISE_EN）通过 Makefile 的 test-with-write-noise 子目标
-  启用，测试代码内部已兼容两种配置。
+Read noise 已退休；cam_read_noise 是纯 pass-through。
+本测试验证查询返回的 scores 与 pure matching 一致。
 """
 
 from __future__ import annotations
@@ -31,83 +13,40 @@ import numpy as np
 from cocotb.clock import Clock
 from cocotb.triggers import RisingEdge
 from model.ref_model import (
-    generate_write_flip_mask,
-    match_top1_with_read_noise,
+    match_top1,
     random_hashes,
     unpack_score_debug_flat,
 )
 from tests.top.utils import (
+    collect_topk,
     dut_hash_bits,
     dut_lanes,
     dut_num_rows,
     get_param,
     query_once,
+    query_topk_once,
     reset_dut,
+    write_row,
     write_rows,
 )
 
 
-# ═══════════════════════════════════════════════════════════════════════════════
-# 测试：读取噪声模型匹配
-# ── READ_NOISE_EN=1 由 Makefile 保证，测试代码中不再重复门控
-# ═══════════════════════════════════════════════════════════════════════════════
-
-
 @cocotb.test()
-async def read_noise_model_match(dut):
-    """读取噪声模型匹配：验证 RTL 的读取噪声行为与 Python 参考模型一致。
-
-    与写入噪声不同，读取噪声发生在查询阶段（每次查询向哈希值注入噪声），
-    因此：
-      - 如果先有写入噪声，存储行已经被翻转过一次
-      - 然后查询时还会再注入一层读取噪声
-      - 两层噪声使用不同的种子（写: 0xB504..., 读: 0x6A09...）
-
-    本测试：
-      1. 用 Python 模型预计算存储后的哈希（含写入噪声）
-      2. 用 match_top1_with_read_noise 预计算含读取噪声的期望结果
-      3. 写入原始值到 RTL，查询，比对结果
-    """
+async def read_path_pass_through_produces_pure_matching(dut):
+    """写 4 行，查询存过的行，验证 Top-1/Top-K 与 pure matching 一致。"""
     cocotb.start_soon(Clock(dut.clk, 10, unit="ns").start())
     await reset_dut(dut)
 
     num_rows = dut_num_rows(dut)
     hash_bits = dut_hash_bits(dut)
-    lanes = dut_lanes(dut)
-    rng = np.random.default_rng(123)
+    rng = np.random.default_rng(42)
     rows = random_hashes(rng, num_rows, width=hash_bits)
 
-    # If write noise is enabled, apply write flip masks to predict stored rows
-    stored_rows = list(rows)
-    if get_param(dut, "WRITE_NOISE_EN", 0):
-        seed = 0xB504_F32D_B504_F32D
-        prng_state = (seed << 64) | seed
-        stored_rows = []
-        for row in rows:
-            flip, prng_state = generate_write_flip_mask(
-                prng_state,
-                hash_bits,
-                get_param(dut, "WRITE_NOISE_BITS", 8),
-                get_param(dut, "WRITE_NOISE_RATE_NUM", 1),
-                get_param(dut, "WRITE_NOISE_RATE_DEN", 100),
-            )
-            stored_rows.append(row ^ flip)
-
-    query = rows[min(5, num_rows - 1)]
-
     await write_rows(dut, rows)
-    top1_index, top1_score, score_debug = await query_once(dut, query)
+    query = rows[min(50, num_rows - 1)]
 
-    expected = match_top1_with_read_noise(
-        query,
-        stored_rows,
-        width=hash_bits,
-        lanes=lanes,
-        noise_bits=get_param(dut, "READ_NOISE_BITS", 8),
-        rate_num=get_param(dut, "READ_NOISE_RATE_NUM", 1),
-        rate_den=get_param(dut, "READ_NOISE_RATE_DEN", 100),
-        seed=0x6A09_E667_F3BC_C909,
-    )
+    top1_index, top1_score, score_debug = await query_once(dut, query)
+    expected = match_top1(query, rows, width=hash_bits)
 
     assert top1_index == expected.top1_index
     assert top1_score == expected.top1_score