fix: close all FPGA timing — CFAR pipeline + CIC reset path (Build 19)

CFAR pipeline fix (clk_100m WNS: -0.331ns → +0.156ns):
- Pre-register col_buf reads during ST_CFAR_THR pipeline stage
- 8 pipeline registers (4 values + 4 valids) break 15-level mux tree
- Delta wires use registered values, eliminating combinatorial depth

CIC reset path fix (clk_mmcm_out0 WNS: -0.074ns → +0.068ns):
- Add reset_h input port to cic_decimator_4x_enhanced.v
- Remove internal wire reset_h = ~reset_n (LUT1 inverter was root cause)
- Wire pre-registered reset_400m from ddc_400m.v into both CIC instances
- 3 sync reset blocks changed from if(!reset_n) to if(reset_h)

Build 19 results (xc7a50tftg256-2, Vivado 2025.2):
- All 5 clock domains timing met, 0 failing endpoints
- WNS: +0.068ns (400MHz), +0.156ns (100MHz), +0.627ns (120MHz)
- Utilization: 66.67% LUT, 22.36% FF, 74% BRAM, 93.33% DSP
- Bitstream: 2,140 KB

9_Firmware/9_2_FPGA/cfar_ca.v

@@ -208,20 +208,31 @@ wire lead_rem_valid = (lead_rem_idx >= 0) && (lead_rem_idx < NUM_RANGE_BINS);
 wire lag_rem_valid  = (lag_rem_idx  >= 0) && (lag_rem_idx  < NUM_RANGE_BINS);
 wire lag_add_valid  = (lag_add_idx  >= 0) && (lag_add_idx  < NUM_RANGE_BINS);
 
-// Safe col_buf read with bounds checking (combinational)
+// Safe col_buf read with bounds checking (combinational — feeds pipeline regs)
 wire [MAG_WIDTH-1:0] lead_add_val = lead_add_valid ? col_buf[lead_add_idx[ROW_BITS-1:0]] : {MAG_WIDTH{1'b0}};
 wire [MAG_WIDTH-1:0] lead_rem_val = lead_rem_valid ? col_buf[lead_rem_idx[ROW_BITS-1:0]] : {MAG_WIDTH{1'b0}};
 wire [MAG_WIDTH-1:0] lag_rem_val  = lag_rem_valid  ? col_buf[lag_rem_idx[ROW_BITS-1:0]]  : {MAG_WIDTH{1'b0}};
 wire [MAG_WIDTH-1:0] lag_add_val  = lag_add_valid  ? col_buf[lag_add_idx[ROW_BITS-1:0]]  : {MAG_WIDTH{1'b0}};
 
-// Net deltas
+// ============================================================================
-wire signed [SUM_WIDTH:0] lead_delta = (lead_add_valid ? $signed({1'b0, lead_add_val}) : 0)
+// PIPELINE REGISTERS: Break col_buf mux tree out of ST_CFAR_CMP critical path
-                                      - (lead_rem_valid ? $signed({1'b0, lead_rem_val}) : 0);
+// ============================================================================
-wire signed [1:0] lead_cnt_delta = (lead_add_valid ? 1 : 0) - (lead_rem_valid ? 1 : 0);
+// Captured in ST_CFAR_THR (col_buf indices depend only on cut_idx/r_guard/r_train,
+// all stable during THR). Used in ST_CFAR_CMP for delta/sum computation.
+// This removes ~6-8 logic levels (9-level mux tree) from the CMP critical path.
+reg [MAG_WIDTH-1:0] lead_add_val_r, lead_rem_val_r;
+reg [MAG_WIDTH-1:0] lag_rem_val_r,  lag_add_val_r;
+reg                 lead_add_valid_r, lead_rem_valid_r;
+reg                 lag_rem_valid_r,  lag_add_valid_r;
 
-wire signed [SUM_WIDTH:0] lag_delta = (lag_add_valid ? $signed({1'b0, lag_add_val}) : 0)
+// Net deltas (computed from registered col_buf values — combinational in CMP)
-                                     - (lag_rem_valid ? $signed({1'b0, lag_rem_val}) : 0);
+wire signed [SUM_WIDTH:0] lead_delta = (lead_add_valid_r ? $signed({1'b0, lead_add_val_r}) : 0)
-wire signed [1:0] lag_cnt_delta = (lag_add_valid ? 1 : 0) - (lag_rem_valid ? 1 : 0);
+                                      - (lead_rem_valid_r ? $signed({1'b0, lead_rem_val_r}) : 0);
+wire signed [1:0] lead_cnt_delta = (lead_add_valid_r ? 1 : 0) - (lead_rem_valid_r ? 1 : 0);
+
+wire signed [SUM_WIDTH:0] lag_delta = (lag_add_valid_r ? $signed({1'b0, lag_add_val_r}) : 0)
+                                     - (lag_rem_valid_r ? $signed({1'b0, lag_rem_val_r}) : 0);
+wire signed [1:0] lag_cnt_delta = (lag_add_valid_r ? 1 : 0) - (lag_rem_valid_r ? 1 : 0);
 
 // ============================================================================
 // NOISE ESTIMATE COMPUTATION (combinational for CFAR mode selection)
@@ -290,6 +301,14 @@ always @(posedge clk or negedge reset_n) begin
         noise_sum_reg  <= 0;
         noise_product  <= 0;
         adaptive_thr   <= 0;
+        lead_add_val_r <= 0;
+        lead_rem_val_r <= 0;
+        lag_rem_val_r  <= 0;
+        lag_add_val_r  <= 0;
+        lead_add_valid_r <= 0;
+        lead_rem_valid_r <= 0;
+        lag_rem_valid_r  <= 0;
+        lag_add_valid_r  <= 0;
         r_guard        <= 4'd2;
         r_train        <= 5'd8;
         r_alpha        <= 8'h30;
@@ -443,6 +462,19 @@ always @(posedge clk or negedge reset_n) begin
             cfar_status <= {4'd4, 1'b0, col_idx[2:0]};
 
             noise_sum_reg <= noise_sum_comb;
+
+            // Pipeline: register col_buf reads for next CUT's window update.
+            // Indices depend only on cut_idx/r_guard/r_train (all stable here).
+            // Breaks the 9-level col_buf mux tree out of ST_CFAR_CMP.
+            lead_add_val_r   <= lead_add_val;
+            lead_rem_val_r   <= lead_rem_val;
+            lag_rem_val_r    <= lag_rem_val;
+            lag_add_val_r    <= lag_add_val;
+            lead_add_valid_r <= lead_add_valid;
+            lead_rem_valid_r <= lead_rem_valid;
+            lag_rem_valid_r  <= lag_rem_valid;
+            lag_add_valid_r  <= lag_add_valid;
+
             state <= ST_CFAR_MUL;
         end
 

9_Firmware/9_2_FPGA/cic_decimator_4x_enhanced.v

@@ -1,6 +1,7 @@
 module cic_decimator_4x_enhanced (
     input wire clk,                 // 400MHz input clock
     input wire reset_n,
+    input wire reset_h,             // Pre-registered active-high reset from parent (avoids LUT1 inverter)
     input wire signed [17:0] data_in,  // 18-bit input
     input wire data_valid,
     output reg signed [17:0] data_out, // 18-bit output
@@ -32,11 +33,15 @@ localparam COMB_WIDTH = 28;
 // adjacent DSP48E1 tiles — zero fabric delay, guaranteed to meet 400+ MHz
 // on 7-series regardless of speed grade.
 //
-// Active-high reset derived from reset_n (inverted).
+// Active-high reset provided by parent module (pre-registered).
 // CEP (clock enable for P register) gated by data_valid.
 // ============================================================================
 
-wire reset_h = ~reset_n;  // active-high reset for DSP48E1 RSTP
+// reset_h is now an input port from parent module (pre-registered active-high).
+// Previously: wire reset_h = ~reset_n; — this LUT1 inverter + long routing to
+// 8 DSP48E1 RSTB pins was the root cause of 400 MHz timing failure (WNS=-0.074ns).
+// The parent ddc_400m.v already has a registered reset_400m derived from
+// the 2-stage sync reset, so we use that directly.
 
 // Sign-extended input for integrator_0 C port (48-bit)
 wire [ACC_WIDTH-1:0] data_in_c = {{(ACC_WIDTH-18){data_in[17]}}, data_in};
@@ -702,7 +707,7 @@ end
 // Sync reset: enables FDRE inference for better timing at 400 MHz.
 // Reset is already synchronous to clk via reset synchronizer in parent module.
 always @(posedge clk) begin
-    if (!reset_n) begin
+    if (reset_h) begin
         integrator_sampled <= 0;
         decimation_counter <= 0;
         data_valid_delayed <= 0;
@@ -757,7 +762,7 @@ end
 // Pipeline the valid signal for comb section
 // Sync reset: matches decimation control block reset style.
 always @(posedge clk) begin
-    if (!reset_n) begin
+    if (reset_h) begin
         data_valid_comb <= 0;
         data_valid_comb_pipe <= 0;
         data_valid_comb_0_out <= 0;
@@ -792,7 +797,7 @@ end
 //   - Each stage: comb[i] = comb[i-1] - comb_delay[i][last]
 
 always @(posedge clk) begin
-    if (!reset_n) begin
+    if (reset_h) begin
         for (i = 0; i < STAGES; i = i + 1) begin
             comb[i] <= 0;
             for (j = 0; j < COMB_DELAY; j = j + 1) begin

9_Firmware/9_2_FPGA/ddc_400m.v

@@ -565,7 +565,8 @@ wire cic_valid_i, cic_valid_q;
 
 cic_decimator_4x_enhanced cic_i_inst (
     .clk(clk_400m),
-    .reset_n(reset_n_400m),
+    .reset_n(reset_n_400m),
+    .reset_h(reset_400m),
     .data_in(mixed_i[33:16]),
     .data_valid(mixed_valid),
     .data_out(cic_i_out),
@@ -574,7 +575,8 @@ cic_decimator_4x_enhanced cic_i_inst (
 
 cic_decimator_4x_enhanced cic_q_inst (
     .clk(clk_400m),
-    .reset_n(reset_n_400m),
+    .reset_n(reset_n_400m),
+    .reset_h(reset_400m),
     .data_in(mixed_q[33:16]),
     .data_valid(mixed_valid),
     .data_out(cic_q_out),

9_Firmware/9_2_FPGA/tb/tb_cic_decimator.v

@@ -36,6 +36,7 @@ module tb_cic_decimator;
     cic_decimator_4x_enhanced uut (
         .clk               (clk),
         .reset_n            (reset_n),
+        .reset_h            (~reset_n),
         .data_in            (data_in),
         .data_valid         (data_valid),
         .data_out           (data_out),