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Jason
abde60dd7e
The CFAR threshold (alpha) lives in a Q4.4 host register and is loaded
from RP_DEF_CFAR_ALPHA / _SOFT at boot (3.0 / 1.5 in Q4.4). With PR-M.2
swapping the Doppler window from a non-canonical "Hamming-ish" LUT
(PSL=-33 dB) to Dolph-Chebyshev 60 dB (PSL=-60 dB), training-cell
contamination from off-Doppler sidelobes drops by 27 dB and the
effective Pfa at the shipped alpha drops accordingly.
This commit is documentation only — defaults are not changed pre-HW.
Two operating-point options for HW bring-up:
(a) Hold alpha — get higher Pd at lower Pfa as a free win.
(b) Lower alpha — recover original Pfa, get even higher Pd.
Recommended bring-up procedure recorded in cfar_ca.v header:
1. Collect noise-only frames (no targets in dwell).
2. Measure empirical Pfa at shipped alpha=3.0 / 1.5.
3. If Pfa < 0.5 x design target, lower alpha; otherwise hold.
Opcodes 0x23 (RP_OP_CFAR_ALPHA) and 0x2D (RP_OP_CFAR_ALPHA_SOFT) let
the host adjust at runtime without firmware change.
Files:
* cfar_ca.v — adds "Doppler-window dependency" block to the header
after the existing "Threshold computation" block.
* radar_params.vh — adds a note above RP_DEF_CFAR_ALPHA pointing at
cfar_ca.v for the rationale.