SolarXiao MPPT and battery controls, 2026-10-21

The Mercerwood SolarXiao 33S repeater now has a native LTC4162-FST charger interface and INA260 battery monitor in both Full and Reduced firmware. All 75 named register fields were read on the board. Supported setting changes passed live readback and persisted across a warm restart. The original charger register values were restored and all test overrides/calibration flags cleared. Three nonce-bound repeater forwarding tests passed at -6 dBm.

Machine-readable acceptance record contains exact build identities, readouts, command replies, fault-test coverage, RF samples, cleanup and limits. See the SolarXiao controls guide for commands, units, permissions, persistence, calibration and telemetry channels.

Qualified firmware and hardware

Item	Result
Source	`ea8176ddc6b2caa7e52f8dcba46178f69f6cbbea`
Target / installed profile	`solarxiao_33S_repeater` / Full
Version	`v1.18.0.1-halo-keymind-cascade-dev-ea8176dd`
Application body hash	`5A46FDAABF34C62D`
Application size	595,040 bytes
Application SHA-256	`d6068baf837c0348ea841a04a2412bd4724a93022f2d8b750af15ca1fb4fbe76`
Full / Reduced qualification	PASS: build, runtime memory, DFU, UF2 and linked capabilities
Native power marker in both images	PASS
Native host test methods	3 PASS, including eight core scenarios and real Wire/atomic-store boundaries; ASan/UBSan
XIAO startup/shutdown checks	6 PASS, including GPIO safety negative controls
Powered USB readings	75 named register fields; FST chemistry code 6, four cells
Settings / persistence	37 commands including 10 rejected writes; readback, restart and exact register restoration PASS
LoRa carrier telemetry	PASS: three replies with all carrier channels 2..13
Repeater forwarding	3 PASS; exact nonce, four-byte route, one target hop
Bootloader	HEAD `b07255d4cdc601f1313e4cbe020caad3b5544821`, CRC `76EBABBF`, preserved

Full has 150,608 internal bytes available against 76,960 required by the runtime memory check; Reduced has 152,256 available. The installed public key, primary radio, RX power saving and bridge settings remained unchanged. Repeating stayed on and TX stayed -6 dBm. Each trace added one direct RX and TX with zero receive errors. The cumulative receive-error counter was 2 after the trace run and 17 after all telemetry work; core error flags remained zero. The trace partner's settings were preserved and endpoints closed.

Powered bench acceptance

The user supplied 13.2 V at SOLAR/VIN with BAT disconnected and USB connected. Initial native readouts were approximately 13.2926 V input, 13.2785 V output, 27.76 C die and 27.73 C modeled NTC temperature. BAT was open: its changing floating/capacitor voltage is not a battery measurement or a charger load test. The charger reported battery_short while BAT was disconnected.

The test exercised force/fast telemetry, MPPT, input-current limiting, manual input-voltage floor, suspend/resume, JEITA selection, manual charge current and cell voltage, C/x threshold, CV/total timers and saved calibration metadata. For example, 13000 mV input floor read back as 13078.1 mV, matching the hardware step. Manual targets of 1000 mA and 3500 mV/cell read back correctly with JEITA off. These are register-interface tests without a connected battery.

Saved policy reloaded after restart with nine register overrides and the explicit calibration-source flag. Every modified register was restored to its captured value, then mppt reset cleared saved overrides and calibration flags. Final MPPT and JEITA were on; force/fast telemetry were off. Host fault tests also simulated a charger reset, read/write faults, ignored writes, corrupt or wrong-size storage, failed atomic publication, identity mismatch, masked-bit preservation, thermal ordering and one-shot/W0C behavior.

Supply state, radio checks and scope

The first install check found the charger unavailable. It restored the verified previous firmware with identity/settings intact; the user then confirmed the bench supply had been off and switched it on. The final firmware installed and passed powered reading/control tests.

During a later interval when the charger was unavailable again, authenticated LoRa CLI returned an explicit unavailable status while INA260 readings remained available. Three telemetry replies carried channel-2 voltage/current/power; charger channels were omitted. Temporary contacts and forwarding connections were removed. One remote version read required a retry.

After the supply was switched on again, authenticated LoRa commands identified FST/four cells and read charger/battery/status values. Three subsequent telemetry replies contained every carrier channel 2..13: input 13.29 V, output 13.27..13.28 V, die 25.4..25.5 C and modeled NTC 24.9 C. Two telemetry attempts missed replies before a successful retry. An earlier powered CLI session also needed retries and missed its first telemetry response; all temporary contacts/forwards were cleaned up. Final USB checks confirmed VIN 13.2926 V, MPPT/JEITA on, zero saved overrides, zero calibration flags and the same firmware/bootloader identities. These results establish successful readout, not a loss-free radio link.

No actual battery charging, loaded-current calibration, resistance measurement or ship-mode entry was tested. The default 10 milliohm sense resistors and 10 kohm / 3490 K NTC model come from reference documentation; the supplied Standard schematic uses a single-cell L42M, not this exact 12 V FSTM revision. Actual carrier component values and the temperature model remain configurable.

The new application was installed by USB DFU. This run does not repeat a full LoRa firmware transfer; the earlier successful HEAD bootloader/OTA transfer is in the separate OTA report. Reduced was build-checked, while live tests used Full. An exploratory Room Server build exceeded its flash/UF2 limits; native power controls are therefore scoped to the requested SolarXiao repeater targets. No Room Server or Companion package is qualified by this report.