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test(fft): PR-L — fix tb_fft_engine N=32→16 dropdown bugs (T-4)

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The TB hard-coded /32.0 in cosine/sine angle math and read out_re[28] /
out_re[30] which don't exist for N=16, so 3/12 checks failed (Test 3
single-tone, Test 7 imag-tone). Pure TB math error — fft_engine.v is
correct (proven by every production MF/Doppler cosim passing bit-exact).

Test 3: /32.0 → /N, peak expected = N/2*1000 = 8000 (not 16000),
        conjugate read at bin N-4=12 (not 28).
Test 7: /32.0 → /N, conjugate peak at bin N-2=14 (not 30).

Result: 12/12 PASS at N=16 with bin 4 = 7997 ≈ 8000.

Closes T-4. Final regression: 42 passed / 0 failed of 42 — first
all-green since PR-Tests-1 exposed hidden failures.
This commit is contained in:
Jason
2026-05-01 15:32:35 +05:45
parent 7660d5dff4
commit ad37f88cd3
1 changed files with 18 additions and 17 deletions
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35
9_Firmware/9_2_FPGA/tb/tb_fft_engine.v
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@@ -292,15 +292,15 @@ initial begin
// ================================================================
// TEST GROUP 3: Single Tone (cosine at bin 4)
// cos(2*pi*4*n/32) -> peaks at bins 4 and N-4=28
// Amplitude 1000 -> each peak = 1000*N/2 = 16000
// cos(2*pi*4*n/N) -> peaks at bins 4 and N-4 (=12 for N=16)
// Amplitude 1000 -> each peak = 1000*N/2 (=8000 for N=16)
// ================================================================
$display("");
$display("--- Test Group 3: Single Tone (bin 4) ---");
for (i = 0; i < N; i = i + 1) begin
// cos(2*pi*4*i/32) in Q15-ish
angle = 6.28318530718 * 4.0 * i / 32.0;
// cos(2*pi*4*i/N) in Q15-ish
angle = 6.28318530718 * 4.0 * i / N;
cos_val = $rtoi($cos(angle) * 1000.0);
in_re[i] = cos_val;
in_im[i] = 16'sd0;
@@ -318,15 +318,16 @@ initial begin
max_mag_bin = i;
end
end
$display(" Tone FFT peak bin: %0d (expect 4)", max_mag_bin);
$display(" Tone FFT bin[4] = %0d + j%0d", out_re[4], out_im[4]);
$display(" Tone FFT bin[28] = %0d + j%0d", out_re[28], out_im[28]);
check(max_mag_bin == 4 || max_mag_bin == 28,
"Tone FFT: peak at bin 4 or 28");
// Bin 4 and 28 should have magnitude ~= N/2 * 1000 = 16000
$display(" Tone FFT peak bin: %0d (expect 4 or %0d)", max_mag_bin, N-4);
$display(" Tone FFT bin[4] = %0d + j%0d", out_re[4], out_im[4]);
$display(" Tone FFT bin[%0d] = %0d + j%0d", N-4, out_re[N-4], out_im[N-4]);
check(max_mag_bin == 4 || max_mag_bin == (N-4),
"Tone FFT: peak at bin 4 or N-4");
// Bin 4 and N-4 should have magnitude ~= N/2 * 1000 (=8000 for N=16)
mag = out_re[4] * out_re[4] + out_im[4] * out_im[4];
check(mag > 15000*15000 && mag < 17000*17000,
"Tone FFT: bin 4 magnitude ~= 16000");
check(mag > ((N*1000/2 - 1000) * (N*1000/2 - 1000)) &&
mag < ((N*1000/2 + 1000) * (N*1000/2 + 1000)),
"Tone FFT: bin 4 magnitude ~= N/2 * 1000");
// ================================================================
// TEST GROUP 4: Roundtrip (FFT then IFFT = identity)
@@ -457,14 +458,14 @@ initial begin
// ================================================================
// TEST GROUP 7: Pure imaginary input
// FFT of j*sin(2*pi*2*n/N) -> peaks at bins 2 and N-2
// FFT of j*sin(2*pi*2*n/N) -> peaks at bins 2 and N-2 (=14 for N=16)
// ================================================================
$display("");
$display("--- Test Group 7: Pure Imaginary Tone (bin 2) ---");
for (i = 0; i < N; i = i + 1) begin
in_re[i] = 16'sd0;
angle = 6.28318530718 * 2.0 * i / 32.0;
angle = 6.28318530718 * 2.0 * i / N;
in_im[i] = $rtoi($sin(angle) * 1000.0);
end
@@ -480,9 +481,9 @@ initial begin
max_mag_bin = i;
end
end
$display(" Imag tone peak bin: %0d (expect 2 or 30)", max_mag_bin);
check(max_mag_bin == 2 || max_mag_bin == 30,
"Imag tone: peak at bin 2 or 30");
$display(" Imag tone peak bin: %0d (expect 2 or %0d)", max_mag_bin, N-2);
check(max_mag_bin == 2 || max_mag_bin == (N-2),
"Imag tone: peak at bin 2 or N-2");
// ================================================================
// TEST GROUP 8: Zero input