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Fix overlap-save: fill full 1024-sample buffer per segment, zero-pad last partial segment

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Previously segment 0 only filled positions [0:895], leaving [896:1023]
as zeros from the initial block. These zeros propagated into the overlap
region of subsequent segments, corrupting the convolution.

Fix: change buffer-full threshold from SEGMENT_ADVANCE (896) to
BUFFER_SIZE (1024). Add zero-padding for the last segment when chirp
data runs out before the buffer is full. Updated testbench accordingly.

Verified: multi-segment 32/32 PASS, integration test 10/10 PASS.
This commit is contained in:
Jason
2026-03-16 19:15:23 +02:00
parent 39f78d4349
commit 17b70bdcff
2 changed files with 63 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files
9_Firmware/9_2_FPGA/matched_filter_multi_segment.v
+29 -15
View File
@@ -213,8 +213,13 @@ always @(posedge clk or negedge reset_n) begin
// evaluated every clock (not gated by ddc_valid) to avoid
// missing the transition when buffer_write_ptr updates via
// non-blocking assignment one cycle after the last write.
//
// Overlap-save fix: fill the FULL 1024-sample buffer before
// processing. For segment 0 this means 1024 fresh samples.
// For segments 1+, write_ptr starts at OVERLAP_SAMPLES (128)
// so we collect 896 new samples to fill the buffer.
if (use_long_chirp) begin
if (buffer_write_ptr >= SEGMENT_ADVANCE) begin
if (buffer_write_ptr >= BUFFER_SIZE) begin
buffer_has_data <= 1;
state <= ST_WAIT_REF;
segment_request <= current_segment[1:0];
@@ -231,27 +236,36 @@ always @(posedge clk or negedge reset_n) begin
`ifdef SIMULATION
$display("[MULTI_SEG_FIXED] End of long chirp reached");
`endif
// If buffer isn't full yet, zero-pad the remainder
// (last segment with fewer than 896 new samples)
if (buffer_write_ptr < BUFFER_SIZE) begin
state <= ST_ZERO_PAD;
`ifdef SIMULATION
$display("[MULTI_SEG_FIXED] Last segment partial: zero-padding from %0d to %0d",
buffer_write_ptr, BUFFER_SIZE - 1);
`endif
end
end
end
end
ST_ZERO_PAD: begin
// For short chirp: zero-pad remaining buffer
input_buffer_i[buffer_write_ptr] <= 16'd0;
input_buffer_q[buffer_write_ptr] <= 16'd0;
buffer_write_ptr <= buffer_write_ptr + 1;
if (buffer_write_ptr >= BUFFER_SIZE - 1) begin
// Done zero-padding
buffer_has_data <= 1;
buffer_write_ptr <= 0;
state <= ST_WAIT_REF;
segment_request <= 0; // Only one segment for short chirp
ST_ZERO_PAD: begin
// Zero-pad remaining buffer (short chirp or last long chirp segment)
input_buffer_i[buffer_write_ptr] <= 16'd0;
input_buffer_q[buffer_write_ptr] <= 16'd0;
buffer_write_ptr <= buffer_write_ptr + 1;
if (buffer_write_ptr >= BUFFER_SIZE - 1) begin
// Done zero-padding
buffer_has_data <= 1;
buffer_write_ptr <= 0;
state <= ST_WAIT_REF;
segment_request <= use_long_chirp ? current_segment[1:0] : 2'd0;
mem_request <= 1;
`ifdef SIMULATION
$display("[MULTI_SEG_FIXED] Zero-pad complete, buffer full");
`endif
end
`endif
end
end
ST_WAIT_REF: begin
9_Firmware/9_2_FPGA/tb/tb_multiseg_cosim.v
+34 -28
View File
@@ -379,8 +379,9 @@ initial begin
// ------ SEGMENT 0 ------
$display("\n --- Segment 0 ---");
// Feed SEGMENT_ADVANCE (896) samples
for (i = 0; i < SEGMENT_ADVANCE; i = i + 1) begin
// Feed BUFFER_SIZE (1024) samples to fill the entire buffer
// (overlap-save fix: seg 0 must fill the full 1024-sample buffer)
for (i = 0; i < FFT_SIZE; i = i + 1) begin
@(posedge clk);
ddc_i <= (i + 1) & 18'h3FFFF; // Non-zero, identifiable: 1, 2, 3, ...
ddc_q <= ((i + 1) * 2) & 18'h3FFFF;
@@ -392,24 +393,19 @@ initial begin
// Verify segment 0 transition
@(posedge clk);
@(posedge clk);
$display(" After feeding 896 samples: state=%0d, segment=%0d, chirp_cnt=%0d",
$display(" After feeding 1024 samples: state=%0d, segment=%0d, chirp_cnt=%0d",
fsm_state, cur_seg, chirp_cnt);
check(cur_seg == 3'd0, "Seg 0: current_segment=0");
// Verify buffer contents for segment 0
// Position 0 should have truncated ddc_i value of sample 0
// ddc_i = 1 (18-bit), truncated: ddc_i[17:2] + ddc_i[1] = 0 + 0 = 0
// ddc_i = 2: [17:2]=0, [1]=1 -> 0+1 = 1
// ddc_i = 4: [17:2]=1, [1]=0 -> 1+0 = 1
// This is just the rounding behavior, verify first few:
// Verify buffer contents for segment 0 — all 1024 positions written
$display(" Buffer[0]=%0d, Buffer[1]=%0d, Buffer[127]=%0d",
buf_probe_i_0, dut.input_buffer_i[1], buf_probe_i_127);
$display(" Buffer[895]=%0d, Buffer[896]=%0d, Buffer[1023]=%0d",
buf_probe_i_895, buf_probe_i_896, buf_probe_i_1023);
// Buffer[896:1023] should be zeros (from initial block, never written in seg 0)
check(buf_probe_i_896 == 16'd0, "Seg 0: buffer[896]=0 (unwritten)");
check(buf_probe_i_1023 == 16'd0, "Seg 0: buffer[1023]=0 (unwritten)");
// Buffer[896:1023] should now be WRITTEN with data (overlap-save fix)
check(buf_probe_i_896 != 16'd0, "Seg 0: buffer[896]!=0 (written with data)");
check(buf_probe_i_1023 != 16'd0, "Seg 0: buffer[1023]!=0 (written with data)");
// Wait for segment 0 processing to complete
seg_out = 0;
@@ -441,21 +437,21 @@ initial begin
check(cur_seg == 3'd1, "Seg 0 done: current_segment=1");
// Verify overlap-save: buffer[0:127] should now contain
// what was in buffer[896:1023] of segment 0 (which was zeros)
$display(" Overlap check: buffer[0]=%0d (expect 0 from seg0 pos 896)",
// what was in buffer[896:1023] of segment 0 (real data, not zeros)
$display(" Overlap check: buffer[0]=%0d (from seg0 pos 896, expect non-zero)",
buf_probe_i_0);
check(buf_probe_i_0 == 16'd0, "Overlap-save: buffer[0]=0 (from seg0[896])");
check(buf_probe_i_0 != 16'd0, "Overlap-save: buffer[0]!=0 (real data from seg0[896])");
// buffer_write_ptr should be 128 (OVERLAP_SAMPLES)
check(buf_wptr == 11'd128, "Overlap-save: write_ptr=128");
// ------ SEGMENT 1 ------
$display("\n --- Segment 1 ---");
// Need to fill from ptr=128 to ptr=896 -> 768 new samples
for (i = 0; i < (SEGMENT_ADVANCE - OVERLAP_SAMPLES); i = i + 1) begin
// Need to fill from ptr=128 to ptr=1024 -> 896 new samples
for (i = 0; i < SEGMENT_ADVANCE; i = i + 1) begin
@(posedge clk);
ddc_i <= ((SEGMENT_ADVANCE + i + 1) * 5) & 18'h3FFFF; // Different pattern
ddc_q <= ((SEGMENT_ADVANCE + i + 1) * 7) & 18'h3FFFF;
ddc_i <= ((FFT_SIZE + i + 1) * 5) & 18'h3FFFF; // Different pattern
ddc_q <= ((FFT_SIZE + i + 1) * 7) & 18'h3FFFF;
ddc_valid <= 1'b1;
end
@(posedge clk);
@@ -463,7 +459,7 @@ initial begin
@(posedge clk);
@(posedge clk);
$display(" After feeding 768 samples: state=%0d, segment=%0d, chirp_cnt=%0d",
$display(" After feeding 896 samples: state=%0d, segment=%0d, chirp_cnt=%0d",
fsm_state, cur_seg, chirp_cnt);
// Wait for segment 1 processing
@@ -495,10 +491,11 @@ initial begin
// ------ SEGMENT 2 ------
$display("\n --- Segment 2 ---");
for (i = 0; i < (SEGMENT_ADVANCE - OVERLAP_SAMPLES); i = i + 1) begin
// Feed 896 new samples (ptr 128 -> 1024)
for (i = 0; i < SEGMENT_ADVANCE; i = i + 1) begin
@(posedge clk);
ddc_i <= ((2 * SEGMENT_ADVANCE + i + 1) * 3) & 18'h3FFFF;
ddc_q <= ((2 * SEGMENT_ADVANCE + i + 1) * 9) & 18'h3FFFF;
ddc_i <= ((FFT_SIZE + SEGMENT_ADVANCE + i + 1) * 3) & 18'h3FFFF;
ddc_q <= ((FFT_SIZE + SEGMENT_ADVANCE + i + 1) * 9) & 18'h3FFFF;
ddc_valid <= 1'b1;
end
@(posedge clk);
@@ -528,17 +525,26 @@ initial begin
end
check(cur_seg == 3'd3, "Seg 2 done: current_segment=3");
// ------ SEGMENT 3 (final) ------
$display("\n --- Segment 3 (final) ---");
for (i = 0; i < (SEGMENT_ADVANCE - OVERLAP_SAMPLES); i = i + 1) begin
// ------ SEGMENT 3 (final — partial, zero-padded) ------
$display("\n --- Segment 3 (final, partial + zero-pad) ---");
// Total consumed so far: 1024 + 896 + 896 = 2816
// Remaining: 3000 - 2816 = 184 new samples
// After feeding 184 samples, chirp_complete fires and zero-padding begins
for (i = 0; i < (LONG_CHIRP_SAMPLES - FFT_SIZE - 2 * SEGMENT_ADVANCE); i = i + 1) begin
@(posedge clk);
ddc_i <= ((3 * SEGMENT_ADVANCE + i + 1) * 11) & 18'h3FFFF;
ddc_q <= ((3 * SEGMENT_ADVANCE + i + 1) * 13) & 18'h3FFFF;
ddc_i <= ((FFT_SIZE + 2 * SEGMENT_ADVANCE + i + 1) * 11) & 18'h3FFFF;
ddc_q <= ((FFT_SIZE + 2 * SEGMENT_ADVANCE + i + 1) * 13) & 18'h3FFFF;
ddc_valid <= 1'b1;
end
@(posedge clk);
ddc_valid <= 1'b0;
// Wait a few clocks for chirp_complete to fire and zero-padding to begin
repeat(5) @(posedge clk);
$display(" After feeding %0d samples: state=%0d, segment=%0d, chirp_cnt=%0d",
LONG_CHIRP_SAMPLES - FFT_SIZE - 2 * SEGMENT_ADVANCE,
fsm_state, cur_seg, chirp_cnt);
seg_out = 0;
wait_count = 0;
while (seg_out < FFT_SIZE && wait_count < TIMEOUT) begin