There are no sensor drivers in the system at present, but now that the
HAL rework is complete I wanted to port a few drivers over to Mynewt
just to properly test the HW and HAL out. Existing sensor drivers is one
of the key factors to draw people into any embedded RTOS/system, so I
think it's important to get this right to pull people into the Mynewt
ecosystem.
I'm curious what kind of organization would make the most sense moving
forward, though. Assuming some drivers are included in the core mynewt
repo instead of being in independent libraries, what would be an ideal
root location to place them in the file structure?
- hw/drivers/sensors ?
The problem is that hw/drivers already has things like adc and uart
implementations or nimble which is quite a different concept, though
it's not entirely inappropriate all the same.
And inside sensors (or wherever) you'll have another problem: should you
have a single flat list of all drivers by device name, or do you want to
organize them by type/manufacturer/etc.:
* hw/drivers/sensors/bmp085/*
* hw/drivers/sensors/bmp280/*
* hw/drivers/sensors/tsl2651/*
* hw/drivers/sensors/lsm303dlhc/*
* hw/drivers/sensors/bno055/*
Or do you want to organize them by family (which is nice in some ways
but very awkward in others with certain SoCs):
* hw/drivers/sensors/pressure/bmp085/*
* hw/drivers/sensors/pressure/bmp280/*
* hw/drivers/sensors/light/tsl2561/*
* hw/drivers/sensors/accelerometers/lsm303dlhc/* <-- This is also a
magnetometer!
* hw/drivers/sensors/orientation???/bno055/* <-- this is an accel, mag
and gyro with sensor fusion for orientation
Or does manufacturer make more sense:
* hw/drivers/sensors/bosch/bmp085/*
* hw/drivers/sensors/bosch/bmp280/*
* hw/drivers/sensors/bosch/bno055/*
* hw/drivers/sensors/taos/tsl2561/* <-- Complicated since Taos was
purchased and is now AMS, which is a recurring theme these days
* hw/drivers/sensors/st/lsm303dlhc/*
It would likely be useful to have some sort of basic meta-data as well
about the sensor types since some ICs can contain multiple sensors, such
as the bmp280 being a pressure sensor but also having temperature data,
or the lsm303dlhc being a 3 axis accelerometer and magnetometer. This
meta-data isn't critical, but could be useful as a filter at some point
using the newt tool or the newt 'newt vals' type functionality.
Adding drivers to the core repo is problematic in that it creates a
maintenance burden, but I think drivers are also a huge pull for people
to use the system and an important reference to keep up to date with
changes in the HAL over time. There should at least be one reference for
each bus like I2C, SPI, ADC and UART (GPS etc.) that makes use of the
power management API, etc. Having a maintained reference driver will
reduce support requirements long term, and ensure best practices are
followed by people contributing other drivers in the future.
Kevin
PS: Some sort of sensor API is also worth considering to have a common
data type and standard SI units and meta-data for all sensors (min/max
data values, output speed, etc.), but that's another discussion entirely.
