feat(hw): add CAM top-level synthesis infrastructure and fix RTL synthesis compatibility

- Add hw/syn/Makefile with hier/flat/full synth targets and artifact mirroring
- Add synth_cam_top_hier.ys for hierarchy-preserving resource estimation on Xilinx 7-series
- Add synth_cam_top_flat.ys for flattened Xilinx 7-series synthesis
- Add cam-synth just target for convenient invocation
- Guard runtime assertions (NUM_ROWS/LANES checks, noise seed checks, NOISE_BITS checks)
  behind SYNTHESIS guard in cam_core_banked, cam_read_noise, cam_write_noise, and noise_mask_grouped
- Fix shadowed 'return' variable in random128 xorshift128 function

hw/rtl/core/cam_core_banked.sv

@@ -24,9 +24,11 @@ module cam_core_banked (
 
     assign wr_ready = 1'b1;
 
+    `ifndef SYNTHESIS
     initial begin
         if (`NUM_ROWS % `LANES != 0) $fatal(1, "NUM_ROWS must be divisible by LANES");
     end
+    `endif
 
     always_ff @(posedge clk) begin
         if (wr_valid) begin
@@ -44,9 +46,11 @@ module cam_core_banked (
             rd_valid_o      <= rd_valid_i;
             rd_lane_valid_o <= rd_valid_i ? {`LANES{1'b1}} : '0;
 
+            `ifndef SYNTHESIS
             if (rd_valid_i && ((rd_base_row_i % `LANES) != 0)) begin
                 $fatal(1, "rd_base_row_i must be LANES-aligned");
             end
+            `endif
 
             for (int lane = 0; lane < `LANES; lane++) begin
                 rd_row_ids_o[lane*`ROW_BITS +: `ROW_BITS] <= rd_base_row_i + lane[(`ROW_BITS)-1:0];

hw/rtl/noise/cam_read_noise.sv

@@ -27,9 +27,11 @@ module cam_read_noise #(
     logic [127:0] random_num [0:`LANES-1];
     logic [(`HASH_BITS)-1:0] mask [0:`LANES-1];
 
+    `ifndef SYNTHESIS
     initial begin
         if (READ_NOISE_SEED == 64'd0) $fatal(1, "READ_NOISE_SEED must be nonzero");
     end
+    `endif
 
     generate
         for (genvar lane = 0; lane < `LANES; lane++) begin : gen_lane_noise

hw/rtl/noise/cam_write_noise.sv

@@ -44,9 +44,11 @@ module cam_write_noise #(
         .mask_o  (flip_mask)
     );
 
+    `ifndef SYNTHESIS
     initial begin
         if (WRITE_NOISE_SEED == 64'd0) $fatal(1, "WRITE_NOISE_SEED must be nonzero");
     end
+    `endif
 
     always_ff @(posedge clk or negedge rst_n) begin
         if (!rst_n) begin

hw/rtl/noise/noise_mask_grouped.sv

@@ -17,6 +17,7 @@ module noise_mask_grouped #(
     localparam int SAMPLE_RANGE     = 1 << SAMPLE_BITS;
     localparam int THRESHOLD        = (NOISE_RATE_NUM * SAMPLE_RANGE) / NOISE_RATE_DEN;
 
+    `ifndef SYNTHESIS
     initial begin
         if (NOISE_BITS <= 0) $fatal(1, "NOISE_BITS must be > 0");
         if (HASH_BITS % NOISE_BITS != 0) $fatal(1, "HASH_BITS must be divisible by NOISE_BITS");
@@ -25,6 +26,7 @@ module noise_mask_grouped #(
         if (NOISE_RATE_DEN <= 0) $fatal(1, "NOISE_RATE_DEN must be > 0");
         if (NOISE_RATE_NUM < 0 || NOISE_RATE_NUM > NOISE_RATE_DEN) $fatal(1, "NOISE_RATE_NUM out of range");
     end
+    `endif
 
     always_comb begin
         mask_o = '0;

hw/rtl/random/random128.sv

@@ -42,7 +42,7 @@ module random128 (
             next_z = w;
             next_w = w ^ (w >> 19) ^ t ^ (t >> 8);
 
-            return {next_x, next_y, next_z, next_w};
+            xorshift128 = {next_x, next_y, next_z, next_w};
         end
     endfunction
 

hw/syn/Makefile

@@ -0,0 +1,76 @@
+#===============================================================================
+# CAM Top Synthesis Makefile
+# Targets: synth, hier, flat, clean
+# Usage:
+#   make -C hw/syn synth                          (defaults, output in build/)
+#   make -C hw/syn synth OUT_DIR=/some/path       (mirror artifacts)
+#   make -C hw/syn synth NUM_ROWS=8192            (override parameter)
+#   make -C hw/syn hier                           (hierarchy-only pass)
+#   make -C hw/syn flat                           (flattened-synthesis pass)
+#   make -C hw/syn clean                          (remove build/)
+#===============================================================================
+
+# ── Configurable variables (defaults) ─────────────────────────────────────────
+YOSYS    ?= yosys
+TOP      ?= cam_top
+NUM_ROWS ?= 4096
+HASH_BITS ?= 512
+LANES    ?= 8
+OUT_DIR  ?= build
+
+# ── TOP enforcement (only cam_top is supported) ───────────────────────────────
+ifneq ($(TOP),cam_top)
+$(error error: only TOP=cam_top is supported)
+endif
+
+# ── Internal build directory ──────────────────────────────────────────────────
+BUILD_DIR := build
+
+# ── Fixed script and artifact names ───────────────────────────────────────────
+HIER_SCRIPT := synth_cam_top_hier.ys
+FLAT_SCRIPT := synth_cam_top_flat.ys
+
+HIER_LOG := yosys_hier.log
+FLAT_LOG := yosys_flat.log
+HIER_JSON := cam_top_hier_resources.json
+FLAT_JSON := cam_top_flat_resources.json
+SYNTH_V   := cam_top_synth.v
+
+ARTIFACTS := $(HIER_JSON) $(FLAT_JSON) $(SYNTH_V) $(HIER_LOG) $(FLAT_LOG)
+
+# ── Yosys command-line defines (always passed) ────────────────────────────────
+# cam_params.svh uses `ifndef guards, so -D on the Yosys CLI overrides defaults.
+# Use -D NAME=value syntax (Yosys 0.62); do NOT use -define.
+YOSYS_DEFINES := -D NUM_ROWS=$(NUM_ROWS) -D HASH_BITS=$(HASH_BITS) -D LANES=$(LANES)
+
+# ── Targets ───────────────────────────────────────────────────────────────────
+.PHONY: synth hier flat clean
+
+# ── Hierarchy resource reference pass ─────────────────────────────────────────
+hier:
+	mkdir -p $(BUILD_DIR)
+	$(YOSYS) $(YOSYS_DEFINES) -l $(BUILD_DIR)/$(HIER_LOG) -s $(HIER_SCRIPT)
+
+# ── Flattened Xilinx synthesis pass ───────────────────────────────────────────
+flat:
+	mkdir -p $(BUILD_DIR)
+	$(YOSYS) $(YOSYS_DEFINES) -l $(BUILD_DIR)/$(FLAT_LOG) -s $(FLAT_SCRIPT)
+
+# ── Full synthesis: hier + flat, then mirror artifacts to OUT_DIR if different ─
+synth: hier flat
+	@if [ "$(abspath $(OUT_DIR))" != "$(abspath $(BUILD_DIR))" ]; then \
+		set -e; \
+		echo "Mirroring artifacts to $(OUT_DIR) ..."; \
+		mkdir -p "$(OUT_DIR)"; \
+		for f in $(ARTIFACTS); do \
+			if [ ! -f "$(BUILD_DIR)/$$f" ]; then \
+				echo "error: missing artifact $(BUILD_DIR)/$$f" >&2; \
+				exit 1; \
+			fi; \
+			cp "$(BUILD_DIR)/$$f" "$(OUT_DIR)/$$f"; \
+		done; \
+	fi
+
+# ── Clean ─────────────────────────────────────────────────────────────────────
+clean:
+	rm -rf $(BUILD_DIR)

hw/syn/synth_cam_top_flat.ys

@@ -0,0 +1,38 @@
+# synth_cam_top_flat.ys — Flattened CAM top synthesis for Xilinx Zynq-7020 / 7-series
+# Run from hw/syn: yosys -s synth_cam_top_flat.ys
+
+# Set include directories before reading RTL
+verilog_defaults -push
+verilog_defaults -add -I../rtl
+verilog_defaults -add -I../rtl/core
+verilog_defaults -add -I../rtl/noise
+verilog_defaults -add -I../rtl/random
+
+# Read RTL sources in canonical order
+read_verilog -sv -D SYNTHESIS ../rtl/random/random128.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/noise_mask_grouped.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/cam_write_noise.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/cam_read_noise.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/cam_core_banked.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/popcount_pipeline.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/match_engine_pipeline.sv
+read_verilog -sv -D SYNTHESIS ../rtl/cam_noisy.sv
+read_verilog -sv -D SYNTHESIS ../rtl/cam_top.sv
+
+# Restore verilog defaults
+verilog_defaults -pop
+
+# Flattened Xilinx synthesis (includes proc, opt, fsm, memory, etc.)
+synth_xilinx -family xc7 -top cam_top -flatten
+
+# Ensure build directory exists for output files
+exec -- mkdir -p build
+
+# Write flattened Verilog netlist
+write_verilog -attr2comment build/cam_top_synth.v
+
+# Resource statistics (JSON to file via tee, not mixed into logs)
+tee -q -o build/cam_top_flat_resources.json stat -tech xilinx -json
+
+# Final checks
+check -noinit

hw/syn/synth_cam_top_hier.ys

@@ -0,0 +1,40 @@
+# synth_cam_top_hier.ys — Hierarchy-preserving CAM top resource reference flow
+# Run from hw/syn: yosys -s synth_cam_top_hier.ys
+
+# Set include directories before reading RTL
+verilog_defaults -push
+verilog_defaults -add -I../rtl
+verilog_defaults -add -I../rtl/core
+verilog_defaults -add -I../rtl/noise
+verilog_defaults -add -I../rtl/random
+
+# Read RTL sources in canonical order
+read_verilog -sv -D SYNTHESIS ../rtl/random/random128.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/noise_mask_grouped.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/cam_write_noise.sv
+read_verilog -sv -D SYNTHESIS ../rtl/noise/cam_read_noise.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/cam_core_banked.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/popcount_pipeline.sv
+read_verilog -sv -D SYNTHESIS ../rtl/core/match_engine_pipeline.sv
+read_verilog -sv -D SYNTHESIS ../rtl/cam_noisy.sv
+read_verilog -sv -D SYNTHESIS ../rtl/cam_top.sv
+
+# Restore verilog defaults
+verilog_defaults -pop
+
+# Hierarchy check and elaboration
+hierarchy -top cam_top -check
+
+# Process and optimize
+proc
+opt
+memory -nomap
+
+# Ensure build directory exists for output files
+exec -- mkdir -p build
+
+# Resource statistics (JSON to file via tee, not mixed into logs)
+tee -q -o build/cam_top_hier_resources.json stat -tech xilinx -json
+
+# Final checks
+check -noinit