Messages in this thread | | | Date | Thu, 17 Mar 2022 23:32:06 -0400 | From | Dan Robertson <> | Subject | Re: [RFC] iio: accel: bma400: patches for todos |
| |
On Fri, Mar 18, 2022 at 03:22:27AM +0530, Jagath Jog J wrote: > Hello, > > To continue the contribution I chose the bma400 accelerometer device driver, > there are multiple todos, so thought of adding support for the same. > Currently, I am able to get the trigger buffer with data ready interrupt, > step counter and event for step change with bma400 accelero breakout board.
This is awesome! Thanks so much for checking out the driver. I enjoyed writing it. It seems like quite a capable device with lots of features I've yet to implement, and I had far less time free for development on the device than I had hoped. Any help would be _greatly_ appreciated.
> Below are the changes I have implemented for the bma400 driver in separate > patches > > 1. Conversion to device-managed function and remove the bma400_remove() > function. > 2. Added trigger buffer support with data ready interrupt. > 3. Added a separate channel for the step counter. > 4. Added event support for step change. > Can I send the above patches for review?
I used the driver for this device as a way to learn, so I by no means claim to be an expert, but I'll do my best to review and test patches sent. At a bare minimum I can be a shoulder to cry on and fellow to commiserate with :-)
> Sorry for all the mistakes that I have made in the previous ds1803 patch > series and I will make sure to avoid all those mistakes. > > In the bma400 driver, I am stuck on one point and your advice will be very > helpful. > > https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-iio > From IIO documentation for accelerometer device the calculation for > final value from the sysfs attributes of the accelerometer device for > the Z-axis will be > (in_accel_z_raw + in_accel_z_offset) * in_accel_scale = 9.8 m/s2 approximately. > > In the mainline kernel bma400 device driver, there are multiple-scale > values for different acceleration ranges +-2g, +-4g, etc. > > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > cat in_accel_scale_available > 0.038357 0.076714 0.153428 0.306856 > > With +-4g range > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > cat in_accel_scale > 0.076714 > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > cat in_accel_z_raw > 519 > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > echo "0.076714 * 506" | bc > 39.277568 > > With +- 2g range > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > echo 0.038357 > in_accel_scale > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > cat in_accel_scale > 0.038357 > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > cat in_accel_z_raw > 1012 > root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# > echo "0.038357 * 1012" | bc > 38.817284 > > The _raw value from the sensor is as per the datasheet but the final value for the > Z axis after applying scale for all ranges is around 38.8 which is not expected. > I tried by placing the sensor in a different position where the X-axis value should > be approximately 9.8 m/s2 but In this case also the value is around 38.8 m/s2 > > Is the above method to calculate the acceleration in the Z-axis correct or > am I missing something?
Based on your tests, a review of the code, and a re-read of the datasheet, I definitely calculated the BMA400_SCALE_MIN and BMA400_SCALE_MAX incorrectly.
> For confirmation I also tested the mpu6050 IMU. > > root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_scale_available > 0.000598 0.001196 0.002392 0.004785 > root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_scale > 0.000598 > root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_z_raw > 16706 > root@raspberrypi:/sys/bus/iio/devices/iio:device1# echo "0.000598 * 16706" | bc > 9.9801 > With MPU6050 I am getting 9.9801 m/s2 which is near to earth's acceleration due > to gravity 9.8 m/s2 > > For BMA400 I recalculated the scale values from sensitivity for different > acceleration ranges > https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bma400-ds000.pdf > > For +-2g - 1 LSB = 0.0095768 m/s2 > For +-4g - 1 LSB = 0.0191536 m/s2 > For +-4g - 1 LSB = 0.0383072 m/s2
Assuming you mean 8g for the last one here.
> Is the above method to calculate the scale values correct or am I missing > something?
Yeah, the scale is definitely off currently.
I think we need to change the following, if I'm reading the datasheet correctly.
- BMA400_SCALE_MIN to 9582 - BMA400_SCALE_MAX to 76659
Great catch and thanks for working on the device!
> Thank you > Jagath
Cheers,
- Dan
| |