tests: per-MCS clean-power-ceiling calibration (adaptive-link recipe)#196
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Automates the #1 hand-tuning chore in the OpenIPC-FPV adaptive-link topic: the universal law "higher MCS => lower max clean power" (the PA garbles dense QAM first), which the community measures by hand per adapter ("raise power until garbage, back off 5") and bakes into per-MCS power tables. tests/per_mcs_power_ceiling.sh reuses this repo's diagnostics: for each MCS it sweeps the flat TXAGC index (DEVOURER_TX_PWR) while a second devourer adapter reports per-frame stats (DEVOURER_STREAM_OUT). The ceiling per MCS is the highest power that still DELIVERS cleanly — the point just before frames garble. Key finding that shaped the metric: the EVM *knee* (PA compression) is nearly the same power for every MCS, so it does NOT show the law; what differs is the decode threshold, so a denser constellation's delivery cliff comes at lower power. Delivery, not the EVM knee, is the right signal. Validated on 8812AU (8x8 sweep, chip-RSSI ground — no SDR, per the B210-front-end-limits lesson): ceiling MCS0-3 = idx56, MCS4 = 44, MCS5-7 = 32 (delivery collapses to 0 frames at idx44 for MCS7). A 24-index (~12 dB) taper, 0 law inversions — reproducing the community shape (Johhn's 8812AU 58@MCS0/1 tapering to 30@MCS5). Output is the mcs->safe-power table an adaptive link consumes; it feeds the runtime controls already shipped (SetTxPowerOffsetQdb baseline + the Jaguar2 per-packet offset). Tooling only, no library change. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Why
From
/tmp/adaptive-link-recipes.md(the OpenIPC-FPV "Adaptive Link" topic): the #1 hand-tuning chore is the universal law "higher MCS ⇒ lower max clean power" — the PA garbles dense QAM first, so each MCS has a power ceiling above which video breaks. The whole ecosystem hand-calibrates this per adapter ("raise power until garbage, back off 5"; e.g. Johhn's 8812AU: 58@MCS0/1 → 30@MCS5) and bakes it into per-MCS power tables (wlan_adapters.yaml). This automates it, reusing the diagnostics this session already shipped.What
tests/per_mcs_power_ceiling.sh— for each MCS, sweep the flat TXAGC index (DEVOURER_TX_PWR) while a second devourer adapter reports per-frame stats (DEVOURER_STREAM_OUT). The ceiling per MCS is the highest power that still delivers cleanly — the point just before frames garble. Output is themcs → safe-powertable + the law-check.The metric matters, and the measurement corrected my first guess: the EVM knee (PA compression) turned out to be nearly the same power for every MCS, so keying on it gave a flat table. What actually differs per MCS is the decode threshold — a denser constellation garbles at lower power — so frame-delivery collapse, not the EVM knee, is the right signal.
Validation (8812AU, 8×8 sweep, chip-RSSI ground — no SDR)
Per-MCS delivery (frames/cell) shows the cliff directly:
RESULT ceiling MCS0=56 → top=32 (drop 24 index steps ≈ 12 dB); 0 law inversions → LAW REPRODUCED.This matches the community's known 8812AU shape.Chip-RSSI is the sensor (not the B210 — its front end limits on near-field frames, measured earlier this session). Fixed near-field geometry is valid: the delivery cliff is the PA's clean limit regardless of distance.
Scope
Tooling only — no library change. The table feeds the runtime controls already shipped:
SetTxPowerOffsetQdb(per-rate baseline, #188) + the Jaguar2 per-packet offset (#194). A runtime per-MCS clamp was considered and rejected: per-MCS TXAGC is individually addressable only on Jaguar1; J2/J3 group rates, so it'd be invasive for little gain. The calibration table is the valuable artifact.🤖 Generated with Claude Code