FlintyLemming/PLFM_RADAR
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Improve timing margins with targeted datapath register tuning

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Reduce routing pressure on CIC/NCO critical paths and move Doppler BRAM read-address registers to sync-reset datapath logic so Build 13 closes with stronger setup/hold slack while preserving functional behavior.
This commit is contained in:
Jason
2026-03-17 23:51:04 +02:00
parent 36ad15247c
commit 254c0e6f03
3 changed files with 58 additions and 30 deletions
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9_Firmware/9_2_FPGA/nco_400m_enhanced.v
+10 -7
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@@ -43,7 +43,8 @@ reg [31:0] phase_accum_reg; // Stage 1 output: registered DSP48E1 P[31:0]
reg [31:0] phase_with_offset; // Stage 2 output: phase_accum_reg + offset
// Stage 3a pipeline registers: registered LUT address + quadrant
reg [5:0] lut_index_pipe;
reg [5:0] lut_index_pipe_sin;
reg [5:0] lut_index_pipe_cos;
reg [1:0] quadrant_pipe;
// Stage 3b pipeline registers: LUT output + quadrant
@@ -105,8 +106,8 @@ wire [5:0] lut_index = (quadrant_w[0] ^ quadrant_w[1]) ? ~lut_address[5:0] : lut
// These wires are driven by lut_index_pipe (registered in Stage 3a), so the
// combinational path is just: lut_index_pipe_reg → LUT6 (distributed RAM read)
// This eliminates the LUT3→LUT6 two-level critical path from Build 8.
wire [15:0] sin_abs_w = sin_lut[lut_index_pipe];
wire [15:0] cos_abs_w = sin_lut[63 - lut_index_pipe];
wire [15:0] sin_abs_w = sin_lut[lut_index_pipe_sin];
wire [15:0] cos_abs_w = sin_lut[63 - lut_index_pipe_cos];
// ============================================================================
// Stage 1: Phase accumulator (DSP48E1) — accumulates FTW each cycle
@@ -265,11 +266,13 @@ end
// ============================================================================
always @(posedge clk_400m or negedge reset_n) begin
if (!reset_n) begin
lut_index_pipe <= 6'b000000;
quadrant_pipe <= 2'b00;
lut_index_pipe_sin <= 6'b000000;
lut_index_pipe_cos <= 6'b000000;
quadrant_pipe <= 2'b00;
end else if (valid_pipe[1]) begin
lut_index_pipe <= lut_index;
quadrant_pipe <= quadrant_w;
lut_index_pipe_sin <= lut_index;
lut_index_pipe_cos <= lut_index;
quadrant_pipe <= quadrant_w;
end
end