diff options
Diffstat (limited to 'cocotb_try')
| -rw-r--r-- | cocotb_try/cic3_pdm.v | 63 |
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 |