Messages in this thread | | | Date | Fri, 18 Mar 2022 03:22:27 +0530 | From | Jagath Jog J <> | Subject | [RFC] iio: accel: bma400: patches for todos |
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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.
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? 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?
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 Is the above method to calculate the scale values correct or am I missing something?
Thank you Jagath
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