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Jason
bb6952753d
cfar_ca.v's GO/SO modes correctly cross-multiply to pick the side with the greater (GO) or lesser (SO) per-cell average, but return that side's RAW SUM as the noise estimate -- not the average. Combined with alpha being pre-baked for the interior training-cell count, this means at edges where the picked side is truncated, effective Pfa shifts by the count ratio (up to ~2x in the first/last r_train bins). CA mode's edge behavior was already documented; GO/SO's was not. Documentation only -- no RTL behavior change. The audit's preferred fix (divide noise_sum by selected_count) is explicitly NOT applied: per-CUT integer divide is expensive in 50T fabric and the affected bins are platform clutter (0..60 m) or noise floor (3012..3072 m) where edge errors are masked by other effects. Operators tuning Pfa have three documented options: (a) accept the asymmetry, (b) host-side skip GO/SO outside r_train..NRANGE-r_train and fall back to CA there, (c) hand-tune alpha per-mode based on observed Pfa drift. Changes: - cfar_ca.v header "CFAR Modes" table: GO/SO now explicitly note that selection is by average but return value is raw sum. - cfar_ca.v header "Edge handling": new GO/SO caveat paragraph. - cfar_ca.v ST_CFAR_THR mode 2'b01/2'b10 selectors: inline AUDIT-C7 comment pointing to header. Verification: full regression 41/41 PASS, 0 lint regressions.