drivers: Harmonize two-point temperature calibration across all sensors.

[nedseb]

Context

The multidriver temperature comparison test (PR #100) revealed discrepancies between sensors on the same board. Some were due to bugs (WSEN-HIDS AUTO_INCREMENT, fixed in #109), others to missing calibration (LIS2MDL empirical offset, fixed in PR #98).

To allow per-board fine-tuning during manufacturing or at runtime, all temperature-capable drivers should expose a uniform two-point calibration interface.

Proposed interface

Every driver with a temperature reading should implement:

def set_temp_offset(self, offset_c):
    """Set a temperature offset in °C (gain remains 1.0)."""
    self._temp_offset = float(offset_c)
    self._temp_gain = 1.0

def calibrate_temperature(self, ref_low, measured_low, ref_high, measured_high):
    """Two-point calibration: compute gain and offset from reference values.

    Args:
        ref_low: reference temperature at the low point (°C).
        measured_low: sensor reading at the low point (°C).
        ref_high: reference temperature at the high point (°C).
        measured_high: sensor reading at the high point (°C).
    """
    self._temp_gain = (ref_high - ref_low) / (measured_high - measured_low)
    self._temp_offset = ref_low - self._temp_gain * measured_low

The temperature() method then applies:

return self._temp_gain * raw_or_factory_value + self._temp_offset

Default values: gain=1.0, offset=0.0 (identity) for sensors with factory calibration,
gain=1.0, offset=25.0 for LIS2MDL (no factory zero point).

Sensors concerned

Sensor	Issue	Factory calibration	Default offset	Status
LIS2MDL	#97	None (raw LSB)	25.0°C	✅ Done (PR #98, updated with two-point)
WSEN-HIDS	#105	Yes (T0/T1 registers)	0.0°C	✅ Done
HTS221	#104	Yes (T0/T1 registers)	0.0°C	✅ Done
WSEN-PADS	#106	Implicit	0.0°C	✅ Done
ISM330DL	#107	None specified	25.0°C	✅ Done
BME280	#108	Yes (trimming)	0.0°C	Tracked separately (blocked by #9)

Acceptance criteria

• lis2mdl: Temperature reading missing offset correction. #97 LIS2MDL — PR lis2mdl: Add temperature offset correction with calibration method. #98
• wsen-hids: Add two-point temperature calibration methods. #105 WSEN-HIDS
• hts221: Add two-point temperature calibration methods. #104 HTS221
• wsen-pads: Add two-point temperature calibration methods. #106 WSEN-PADS
• ism330dl: Add two-point temperature calibration methods. #107 ISM330DL
• bme280: Add two-point temperature calibration methods. #108 BME280 — Tracked separately, blocked by driver implementation (bme280: Add BME280 temperature, humidity and pressure sensor driver #9)

Resolution

All existing drivers now implement the harmonized set_temp_offset() / calibrate_temperature() interface. The BME280 calibration is tracked in #108 and will be implemented when the BME280 driver (#9) is completed.

Related

• PR tests: Add multidriver temperature comparison scenario for calibration. #100 — Multidriver temperature comparison test
• wsen-hids: Fix missing AUTO_INCREMENT bit in multi-byte register reads. #109 — WSEN-HIDS AUTO_INCREMENT bug fix

[nedseb]

All 5 existing temperature drivers now implement the harmonized set_temp_offset() / calibrate_temperature() interface. The BME280 calibration is tracked separately in #108 (blocked by #9). Closing this umbrella issue.