Replace direct !reset_n async sense with a registered active-high reset_h
(max_fanout=50) in nco_400m_enhanced, cic_decimator_4x_enhanced, and
ddc_400m. The prior single-LUT1 / 700+ load net was the root cause of
WNS=-0.626 ns in the 400 MHz clock domain on the xc7a50t build. Vivado
replicates the constrained register into ≈14 regional copies, each driving
≤50 loads, closing timing at 2.5 ns.
Change radar_system_top default USB_MODE from 0 (FT601) to 1 (FT2232H).
FT601 remains available for the 200T premium board via explicit parameter
override; the 50T production wrapper already hard-codes USB_MODE=1.
Regression: add usb_data_interface_ft2232h.v to PROD_RTL lint list and
both system-top TB compile commands; fix legacy radar_system_tb hierarchical
probe from gen_ft601.usb_inst to gen_ft2232h.usb_inst.
Golden reference files (rtl_bb_dc.csv, rx_final_doppler_out.csv,
golden_doppler.mem) regenerated to reflect the +1-cycle registered-reset
boundary behaviour; Receiver golden-compare passes 18/18 checks.
All 25 regression tests pass (0 failures, 0 skipped).
Jason
703130307c