1 files changed, 20 insertions, 43 deletions

diff --git a/cocotb_try/cic3_pdm.v b/cocotb_try/cic3_pdm.v
index c53e867..adcc74e 100644
--- a/cocotb_try/cic3_pdm.v
+++ b/cocotb_try/cic3_pdm.v
@@ -2,12 +2,11 @@ module cic3_pdm (
     input  wire        clk,           // PDM clock
     input  wire        rst,           // active-high synchronous reset
     input  wire        pdm_in,        // 1-bit PDM data input
-    input  wire [7:0]  hpf_alpha,     // HPF coefficient (0-255, 255=bypass)
+
     input  wire [2:0]  scale_shift,   // Right shift amount (0-7 bits)
     output reg  signed [15:0] pcm_out, // Decimated PCM output
     output reg         pcm_valid       // Output valid pulse
 );
-
     // CIC filter parameters
     localparam DECIMATION = 64;
     localparam CIC_WIDTH = 17;  // 17 bits for safe margin against overflow
@@ -25,23 +24,10 @@ module cic3_pdm (
     reg signed [15:0] scaled_out;
     reg cic_valid;
     
-    // Leaky integrator HPF registers
-    reg signed [23:0] hpf_integrator;  // 24-bit for precision
-    reg signed [15:0] hpf_output;
-    
-    // HPF calculation wires
-    wire signed [8:0] hpf_complement;
-    wire signed [23:0] hpf_scaled_input;
-    wire signed [23:0] hpf_dc_estimate;
-    /* verilator lint_off UNUSEDSIGNAL */
-    wire signed [23:0] hpf_temp_result;
-    /* verilator lint_on UNUSEDSIGNAL */
+    // DC removal filter registers
+    reg signed [19:0] dc_accumulator;  // 20-bit to prevent overflow
+    reg signed [15:0] dc_estimate;
     
-    // HPF wire assignments
-    assign hpf_complement = 9'd256 - {1'b0, hpf_alpha};
-    assign hpf_scaled_input = {{8{scaled_out[15]}}, scaled_out};
-    assign hpf_dc_estimate = hpf_integrator >>> 8;
-    assign hpf_temp_result = hpf_scaled_input - hpf_dc_estimate;
     wire signed [CIC_WIDTH-1:0] pdm_signed = pdm_in ? 17'sd1 : -17'sd1;
     
     // CIC Integrator stages (run at PDM rate)
@@ -92,44 +78,35 @@ module cic3_pdm (
         case (scale_shift)
             3'd0: scaled_out = cic_out[15:0];
             3'd1: scaled_out = cic_out[16:1];
-            3'd2: scaled_out = {{1{cic_out[16]}}, cic_out[16:2]};  // Sign extend from bit 16
-            3'd3: scaled_out = {{2{cic_out[16]}}, cic_out[16:3]};  // Sign extend from bit 16  
-            3'd4: scaled_out = {{3{cic_out[16]}}, cic_out[16:4]};  // Sign extend from bit 16
-            3'd5: scaled_out = {{4{cic_out[16]}}, cic_out[16:5]};  // Sign extend from bit 16
-            3'd6: scaled_out = {{5{cic_out[16]}}, cic_out[16:6]};  // Sign extend from bit 16
-            3'd7: scaled_out = {{6{cic_out[16]}}, cic_out[16:7]};  // Sign extend from bit 16
+            3'd2: scaled_out = {{1{cic_out[16]}}, cic_out[16:2]};
+            3'd3: scaled_out = {{2{cic_out[16]}}, cic_out[16:3]};
+            3'd4: scaled_out = {{3{cic_out[16]}}, cic_out[16:4]};
+            3'd5: scaled_out = {{4{cic_out[16]}}, cic_out[16:5]};
+            3'd6: scaled_out = {{5{cic_out[16]}}, cic_out[16:6]};
+            3'd7: scaled_out = {{6{cic_out[16]}}, cic_out[16:7]};
         endcase
     end
     
-    // Leaky integrator-based DC blocker
-    // y[n] = x[n] - dc_estimate
-    // dc_estimate[n] = alpha/256 * dc_estimate[n-1] + (1-alpha/256) * x[n]
+    // DC removal filter - runs at decimated rate
     always @(posedge clk) begin
         if (rst) begin
-            hpf_integrator <= 0;
-            hpf_output <= 0;
+            dc_accumulator <= 20'sd0;
+            dc_estimate <= 16'sd0;
             pcm_out <= 0;
             pcm_valid <= 0;
         end else begin
             pcm_valid <= 0;
             
             if (cic_valid) begin
-                if (hpf_alpha == 8'd255) begin
-                    // Bypass HPF completely
-                    pcm_out <= scaled_out;
-                end else begin
-                    // Update leaky integrator (DC estimate)
-                    // integrator = alpha * integrator + (256-alpha) * input
-                    hpf_integrator <= (hpf_alpha * hpf_dc_estimate) + 
-                                     (hpf_complement * hpf_scaled_input);
-                    
-                    // Output = input - DC estimate
-                    hpf_output <= hpf_temp_result[15:0];
-                    pcm_out <= hpf_output;
-                end
+                // Update DC estimate using leaky integrator
+                // acc = acc - acc/16 + scaled_out
+                dc_estimate <= dc_accumulator[19:4];  // Divide by 16
+                dc_accumulator <= dc_accumulator - {{4{dc_estimate[15]}}, dc_estimate} + {{4{scaled_out[15]}}, scaled_out};
+                
+                // Output is scaled CIC output minus DC estimate
+                pcm_out <= scaled_out - dc_estimate;
                 pcm_valid <= 1;
             end
         end
     end
-
 endmodule