Add support for related sensors (BMA42x)

[thecodechemist99]

Goal

I’m working on a PineTime project and would like to add support for the BMA421 (I just realized my PineTime still has the older sensor) and maybe also BMA425 sensors (to be able to support newer models, too) to this driver.

Implementation

General

The configuration files for both sensors are available, e.g. from this project.

BMA425

I went through the BMA425 datasheet pretty thoroughly and the relevant parts seem to be identical on first glance.
The only difference I found so far to the driver (though the datasheet is identical to the BMA423’s in this regard?) is the AccelConfigBandwidth enum. The datasheet specifies the values as 0x00, 0x01, 0x02 and so on, while the driver sets them to 0x00, 0x10, 0x20 and so on.

BMA421

Unfortunately, I couldn’t find a publicly available full datasheet for this sensor, only a two-page overview. But a first test with the config file linked above and the different chip id (0x11) added to ChipId worked fine at least for initializing the sensor.

Integration with the existing driver

I think we should discuss the best way to integrate the additional hardware into the driver. These are my suggestions, feel free to comment on them and make different suggestions if you think they would work better. Also, please add anything you deem relevant that I might have overlooked.

Config Files

The additional config files can just be added to config.rs aside the existing one.

Feature Flags

I would add feature flags for the different models. These could be used to determine which config file to read, and for other possibly necessary, model-depending changes.
The bma423 flag can be set as a default.

Chip ID

The chip id for the BMA421 can just be added to the ChipId struct as an additional entry. The BMA423 and BMA425 apparently have the same id.

Restrictions

Right now I can only test the BMA421 implementation on hardware.

[pyaillet]

Great summary!

The original driver came from experimentations made with a t-watch, but I happen to also have a PineTime and the DevKit 😄
I never took the time to play with it though. I think it's the occasion :)

Beside this, I agree with your plan. Maybe when enough progress is made we could be able to rename the crate to bma42x-rs.

[thecodechemist99]

That’s convenient 😄. Do you know how long you’ve had these? The wiki says they changed the sensor from the BMA421 to the BMA425 in July 2021. I actually bought my DevKit only a year ago, but apparently the DevKit shipped at least until then still with the old sensor inside.

Then my pinetime-rust repository might be a good place to look at 😉. Check the dev branch for the most up-to-date version. I’m currently working on getting all the hardware running with rust. The accelerometer is actually the last still entirely missing device.

Good idea 👍 .