Kestrel: enable the 8852C frame-free NHM floor on 2.4 GHz

src/kestrel/RtlKestrelDevice.cpp

@@ -372,16 +372,19 @@ RxEnergy RtlKestrelDevice::GetRxEnergy() {
    * env-monitor. Frame-free, BB-driven, no clock-stop -> no wedge.
    * ~mntr_time (100 ms) of control-thread wait; opt-in. Guard to a plausible
    * idle-floor band so a not-ready/garbage report never emits a fake dBm.
-   * C8852B only: the NHM triggers on the C8852C but its nhm_pwr reads ~23 dB
-   * high (on-air ch36 the NHM reads -70 dBm while the passive floor and the
-   * 8852B NHM both read -93). The offset is in the NHM's raw HW gain reference,
-   * not the SW path (halbb_env_mntr treats the 8852C identically to the 8852B)
-   * and not the front-end gain (the physts RSSI is correct — the passive floor
-   * cross-matches the 8852B NHM within ~1 dB). The vendor has no 8852C NHM
-   * offset; it is a deeper RF-cal reference. The C8852C's absolute floor is met
-   * by the passive rssi-snr floor (GetRxQuality), so the frame-free NHM stays
-   * 8852B-only rather than emit the wrong -70. */
-  if (_cfg.rx.abs_noise_floor && _variant == kestrel::ChipVariant::C8852B) {
+   *
+   * The C8852C NHM is band-limited to 2.4 GHz. On-air it reads correctly there
+   * (cross-matches its passive floor within ~2 dB, stable), but on 5 GHz the
+   * AGC drifts ~1.5 s after a channel tune and LOCKS the NHM ~24 dB high (a
+   * bimodal gain-state lock, not a fixed offset the halbb SW path handles — it
+   * treats the 8852C identically to the 8852B, and the physts RSSI is correct;
+   * only a full set_channel re-tune resets it, and RX traffic re-drives it). So
+   * the 8852C emits the NHM on 2.4 GHz and falls back to the passive rssi-snr
+   * floor (GetRxQuality) on 5 GHz. The C8852B NHM is correct on both bands. */
+  const bool nhm_supported =
+      _variant == kestrel::ChipVariant::C8852B ||
+      (_variant == kestrel::ChipVariant::C8852C && _channel.Channel <= 14);
+  if (_cfg.rx.abs_noise_floor && nhm_supported) {
     int8_t nf = 0;
     if (_hal.nhm_noise_floor(nf) && nf <= -60 && nf >= -105) {
       e.abs_noise_floor_dbm = nf;

tests/kestrel_nhm_2g_onair.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+# Validate the band-gated Kestrel active NHM floor (DEVOURER_RX_NOISE_FLOOR ->
+# RxEnergy.abs_noise_floor_dbm, emitted in rx.quality as abs_noise_floor_dbm):
+#   - C8852C: NHM emitted on 2.4 GHz (validated correct), NULL on 5 GHz (the AGC
+#     gain-lock reads ~24 dB high there, so it falls back to the passive floor).
+#   - C8852B: NHM emitted on both bands (unchanged).
+#
+# Usage: sudo -v && tests/kestrel_nhm_2g_onair.sh
+set -u
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+OUT="${NHM2G_OUT:-/tmp/devourer-nhm-2g}"; mkdir -p "$OUT"
+CH_24="${CH_24:-6}" CH_5="${CH_5:-36}" DUR="${DUR:-8}"
+VID=0x35bc; C_PID=0x0101; B_PID=0x0108
+
+plugged() { lsusb -d "$(printf '%04x:%04x' "$1" "$2")" >/dev/null 2>&1; }
+unbind() { local pid="$1" d p i
+  for d in /sys/bus/usb/devices/*/idProduct; do p=$(cat "$d" 2>/dev/null) || continue
+    [ "$p" = "${pid#0x}" ] || continue
+    for i in "$(dirname "$d")":*; do
+      [ -e "$i/driver" ] && sudo sh -c "echo '$(basename "$i")' > '$i/driver/unbind'" 2>/dev/null || true
+    done; done; }
+
+cat >"$OUT/med.py" <<'PYEOF'
+import json,sys,statistics as st
+v=[]
+for l in sys.stdin:
+    try: x=json.loads(l).get("abs_noise_floor_dbm")
+    except: continue
+    if isinstance(x,(int,float)): v.append(x)
+print(f"{int(st.median(v))}" if v else "null")
+PYEOF
+
+nhm() { # $1=pid $2=ch -> median abs_noise_floor_dbm or "null"
+  unbind "$1"
+  sudo env DEVOURER_VID="$VID" DEVOURER_PID="$1" DEVOURER_CHANNEL="$2" \
+    DEVOURER_RXQUALITY=1 DEVOURER_RX_NOISE_FLOOR=1 DEVOURER_RX_ENERGY_MS=500 \
+    timeout "$DUR" "$ROOT/build/rxdemo" 2>/dev/null | grep '"ev":"rx.quality"' \
+    | python3 "$OUT/med.py"; }
+
+echo "== building rxdemo =="; cmake --build "$ROOT/build" -j --target rxdemo >/dev/null || exit 1
+printf "\n%-8s %-16s %-16s\n" DIE "2.4G(ch$CH_24)" "5G(ch$CH_5)"
+c24="skip"; c5="skip"; b24="skip"; b5="skip"
+if plugged "$VID" "$C_PID"; then c24=$(nhm "$C_PID" "$CH_24"); c5=$(nhm "$C_PID" "$CH_5"); fi
+if plugged "$VID" "$B_PID"; then b24=$(nhm "$B_PID" "$CH_24"); b5=$(nhm "$B_PID" "$CH_5"); fi
+printf "%-8s %-16s %-16s\n" C8852C "$c24" "$c5"
+printf "%-8s %-16s %-16s\n" C8852B "$b24" "$b5"
+
+echo
+python3 - "$c24" "$c5" "$b24" "$b5" <<'PYEOF'
+import sys
+c24,c5,b24,b5=sys.argv[1:5]
+def num(x):
+    try: return int(x)
+    except: return None
+ok=True
+n=num(c24)
+if n is not None and -100<=n<=-80: print(f"  C8852C 2.4G NHM {c24} dBm -> PASS (emitted, plausible)")
+else: print(f"  C8852C 2.4G NHM {c24} -> FAIL (expected a plausible -80..-100)"); ok=False
+if c5=="null": print(f"  C8852C 5G NHM null -> PASS (gated off, uses passive floor)")
+else: print(f"  C8852C 5G NHM {c5} -> FAIL (expected null; the 5G gain-lock)"); ok=False
+if b24!="skip":
+    print(f"  C8852B 2.4G {b24} / 5G {b5} (reference; expect both emitted)")
+print("  =>", "ALL PASS" if ok else "CHECK ABOVE")
+PYEOF