Fix temperature sign in bme280 and bmp280 drivers

[brghena]

Pull Request Overview

Temperature is a 20-bit, two's complement value in both the BME280 and BMP280 chips. Further, the datasheets provide example code, which treats all units as signed, 32-bit values while doing math.

This came up when considering #2967 and looking through temperature sensor drivers and datasheets. I wanted to decouple it though, since it's chip-specific changes.

Functionally, this PR should make no difference except for temperatures below zero Celsius. They still won't work right until #2967 lands, but that's an easy fix.

Testing Strategy & Help Wanted

I don't have hardware for these sensors! @dcz-self and @alistair23 are you able to ensure I didn't break temperature readings?

TODO or Help Wanted

• [ ] Test BME280
• [ ] Test BMP280

Documentation Updated

• [N/A] Updated the relevant files in /docs, or no updates are required.

Formatting

• [X] Ran make prepush.

[brghena]

For double-checking me, see pages 25-26 here: https://www.mouser.com/datasheet/2/783/BST-BME280-DS002-1509607.pdf and page 22 here: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bmp280-ds001.pdf

[brghena]

Thanks so much for testing this @alistair23. Would you mind running the temperature app again now that I added a commit?

[alistair23]

Same problem, I get values like this:

check run BME280 Temperature... 
Temperature: 9330
    [ok]
check run BME280 Humidity... 
Humidity: 4294967186
    [ok]

[brghena]

Alright, I've got a BME280 breakout coming and will debug. Thanks for trying this out @alistair23

[phil-levis]

@brghena ping!

[hudson-ayers]

@brghena reminder on this if you get the chance to work on it! Once it is ready again feel free to re-assign Johnathan