ADR-108: after the first successful gain-lock on FW, save the AGC and
FFT median values to NVS (namespace "csi_cfg", keys "gl_agc" / "gl_fft").
On every subsequent boot the FW loads them and immediately calls
phy_force_rx_gain / phy_fft_scale_force without waiting 300 packets
(~3-12 s) for fresh calibration.
Mechanics:
rv_gain_load_from_nvs / rv_gain_save_to_nvs — small NVS helpers in
the gain-lock module.
rv_gain_lock_process — `s_nvs_checked` static gate triggers a one-
shot load on the first packet after boot. If
a saved AGC ≥ MIN_SAFE_AGC is found, lock
immediately + mark locked. Otherwise fall
through to the existing 300-packet sampler.
Existing lock branch — after the median + force_*, save to NVS so
the next boot has the values.
Verified live: second OTA → 44 Hz raw CSI at WS in the first 3-s
sample after boot (was ~5-12 s gap before). Both nodes flashed via
WiFi (no USB), no MIN_SAFE_AGC skip in operator's deployment (AGC=44).
Tradeoff: NVS values are tied to sensor location + AP MAC + channel +
antenna. If the operator moves the sensor or swaps the AP, stale
values may be slightly off-optimal until they re-trigger calibration.
Today: erase NVS keys via console; future: dedicated FW endpoint.
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