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VersBinarii / bme280-rs

A platform agnostic Rust driver for the Bosch BM[PE]-280
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Fix sign extension of h4 and h5 calibration value #24

Closed mbuesch closed 1 year ago

mbuesch commented 1 year ago

The 12 bit signed values h4 and h5 are meant to be sign extended to signed 16 bit. The data sheet is ambiguous about this, but the official driver provided by Bosch does sign extension:

https://github.com/BoschSensortec/BME280_driver/blob/c47f06eb44fc96970f0abfcc941ec16425b2a9e6/bme280.c#L1528

Also see this example code for why this step cast makes a difference: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=99d2c26c65a324288c1a9c3a08eeb0dc

h_data[4] doesn't strictly need this step cast, but I included it for symmetry. The new mask 0xF0 is necessary with this sign extension cast.

This bug is very similar to this other bug in this other crate: https://github.com/newAM/bme280-multibus/pull/22