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Jason
9c231d85db
The PR-Z A6 e2e test (tb_e2e_dsp_to_host) exposed that the wire-format
cfar_dense map emitted by usb_data_interface_ft2232h was all-zero for
our deterministic single-target stimulus, even though cfar_ca's
in-flight outputs showed CONFIRMED at the expected cells (verified via
in-TB capture, E5/E6 PASS).
Deep instrumented debug (BRAM-WRITE, BRAM-READ, EGRESS-CAP probes)
revealed THREE independent bugs that combined to produce the all-zero
wire output. Each bug alone would have been visible; the way they
compounded made the symptom look like a single coarse failure.
Bug A — stale write address (radar_system_top.v):
usb_inst.range_bin_in/doppler_bin_in were tied to notched_*_bin
(= rx_*_bin = doppler_processor outputs). After doppler returns to
S_IDLE its `output reg`s hold their last-driven values (511, 47).
cfar_ca's CMP-phase emit (cycles ~520..73520 after frame_complete)
fires cfar_valid with detect_range/detect_doppler set to its own
per-cell scan counters, but those outputs were dangling — usb's
RMW saw the doppler stale (511, 47) and slammed every cfar write
to byte_addr {511, 47[5:2]} = bram[8187], past the 6144-byte wire
range entirely.
Fix: register cfar_detect_range/doppler in lockstep with the existing
rx_detect_valid/rx_detect_class registration block (clk_100m_buf
domain), then mux them into usb_inst.range_bin_in/doppler_bin_in on
rx_detect_valid. doppler-magnitude write path is unaffected because
doppler_valid and rx_detect_valid are mutually exclusive (BUFFER vs
CMP phases of cfar_ca).
Bug B — BRAM read pipeline lag (usb_data_interface_ft2232h.v):
The detect_rd_data <= detect_bram[detect_rd_addr] BRAM read port has
1-cycle latency. WR_DETECT_DATA's emit FSM advanced detect_rd_addr
and read detect_rd_data in the SAME edge — so cycle K read bram[K-2]
(the addr from cycle K-1's commit) instead of bram[K-1]. Result:
every cfar wire byte = bram[N-1] instead of bram[N], shifting the
entire 6144-byte detect section +1 byte = +4 doppler bins. Doppler
hides this naturally because its 2-byte-per-cell rhythm gives BRAM a
free settling cycle between addr-set and emit-read.
Fix: pre-load detect_rd_addr <= 1 and det_doppler_byte_idx <= 1 at
every WR_DETECT_DATA entry transition (HDR direct, RANGE direct,
DOPPLER → DETECT). BRAM produces bram[0] for the first emit cycle
(settled since reset because detect_rd_addr was 0 throughout the
preceding section) while the addr advance schedules bram[1] for the
second emit cycle — and from then on the FSM's natural advance
pattern keeps the pipeline aligned, including across the per-range
boundary (det_doppler_byte_idx == DET_BYTE_LAST_PER_RANGE).
Bug C — detect_clearing window overlaps cfar's first 4 columns:
detect_clearing fired 1 cycle after frame_complete and ran for 8192
clk cycles (1 byte/cycle). cfar_valid writes were gated on
`!detect_clearing` (line 512). cfar's CMP-phase emits start at
frame_complete + ~520 cycles and run for ~73000 cycles, so the
first ~7672 cycles (≈ 4 doppler columns) of cfar pulses were
silently dropped. Test stimulus lit (67, 2/3) for sub-frame 0, all
inside the clearing window → bytes lost. (67, 18/19) and (67, 34/35)
for SF1/SF2 fell after clearing → captured correctly. Visible as
one-byte mismatch (0x0A expected, 0x00 captured) at offset 49965
(= cfar byte 804 = range 67, doppler 0..3) once Bugs A and B were
fixed.
Fix: move detect_clearing trigger from "1 cycle after frame_complete"
to wr_done_pulse (USB-transfer-complete edge already CDC'd into clk
via the AUDIT-C12 wr_done_sync chain). Clearing now runs in the dead
zone after USB has finished reading frame N's BRAM, well before
frame N+1's cfar starts CMP (~480k cycles of margin at 178 fps).
First frame after reset relies on BRAM init=0 — added explicit
initial block under `ifdef SIMULATION so iverilog matches Vivado's
synthesis default.
Test infrastructure:
- tb/tb_e2e_dsp_to_host.v new — deterministic single-target stimulus
fed through the back-half of the radar pipeline (range_decim → MTI
→ doppler → DC-notch → cfar → registered sync → usb), 16 in-TB
asserts + bit-exact byte capture.
- tb/cosim/gen_e2e_stimulus.py / gen_e2e_expected.py new — Python
deterministic stim + bit-exact frame golden.
- tb/cosim/tb_e2e_dsp_to_host_parse.py new — parses captured frame
via radar_protocol, runs 12 strict-bit-equality checks plus 16
semantic checks (target == CONFIRMED, neighbors == NONE,
DC-notched bins == NONE, etc).
- run_regression.sh — A6 hookup + retired the two zero-assertion
radar_system_tb USB_MODE=0/1 smoke runs and the 3-liveness-only
tb_system_dataflow (subsumed by A6's stronger checks). Saves
~7 min wall.
Verification:
- Local iverilog: in-TB 16/16 PASS, parser strict 28/28 PASS.
- Remote Vivado 2025.2 xsim (Artix-7 target): in-TB 16/16 PASS,
parser strict 28/28 PASS.
- Full regression: 41 / 0 / 0.
The MODEL_USB_CFAR_BUG bug-model flag (used to keep the regression
green during development against buggy production) is removed — the
test is now strict bit-exact against the post-fix wire format.