TS-7250-V3 Magnetometer

This board includes an ST IIS2MDCTR 3 axis magnetometer.

The magnetometer is accessed through Linux's industrial IIO framework as lis2mdl_magn with channels:

• magn_x
• magn_y
• magn_z
• timestamp

For example:

root@tsimx6ul:~# iio_attr -c lis2mdl_magn -c magn_x
dev 'lis2mdl_magn', channel 'magn_x' (input), attr 'raw', value '630'
dev 'lis2mdl_magn', channel 'magn_x' (input), attr 'scale', value '0.001500'
root@tsimx6ul:~# iio_attr -c lis2mdl_magn -c magn_y
dev 'lis2mdl_magn', channel 'magn_y' (input), attr 'raw', value '-165'
dev 'lis2mdl_magn', channel 'magn_y' (input), attr 'scale', value '0.001500'
root@tsimx6ul:~# iio_attr -c lis2mdl_magn -c magn_z
dev 'lis2mdl_magn', channel 'magn_z' (input), attr 'raw', value '9'
dev 'lis2mdl_magn', channel 'magn_z' (input), attr 'scale', value '0.001500'

This shows a snapshot of the x, y, z values. To get the real world value, multiply the scale * the raw value. In this case:

• X: 0.945 mG (milligauss)
• Y: -0.2475 mG
• Z: 0.0135 mG

This driver also supports pulling continuous samples using the buffer interface. These can be accessed using iio_readdev:

iio_readdev lis2mdl_magn -T 0 -s 128 > samples.bin

The format of this file is specified with iio_attr:

root@tsimx6ul:~# iio_attr -c ism330dlc_accel
dev 'ism330dlc_accel', channel 'accel_x' (input, index: 0, format: le:S16/16>>0), found 4 channel-specific attributes
dev 'ism330dlc_accel', channel 'accel_y' (input, index: 1, format: le:S16/16>>0), found 4 channel-specific attributes
dev 'ism330dlc_accel', channel 'accel_z' (input, index: 2, format: le:S16/16>>0), found 4 channel-specific attributes
dev 'ism330dlc_accel', channel 'timestamp' (input, index: 3, format: le:S64/64>>0), found 0 channel-specific attributes

The samples are padded to the nearest 8-bytes, so this means the binary format is:

Bits	Description
15:0	accel_x, little endian, signed
15:0	accel_y, little endian, signed
15:0	accel_z, little endian, signed
63:0	timestamp, little endian, signed
15:0	Padding

The unix utility hexdump supports formatting options which can parse these fields:

root@tsimx6ul:~# hexdump samples.bin --format '1/2 "X:%d " 1/2 "Y:%d " 1/2 "Z:%d " 1/8 "TS:%d" 1/2 "" "\n"' | head -n 4
X:-95 Y:-163 Z:8221 TS:200185381271666439
X:-107 Y:-147 Z:8248 TS:200190332264480519
X:-100 Y:-155 Z:8263 TS:200195283888013063
X:-95 Y:-159 Z:8253 TS:200200232540667655

This gives the raw values which can then be multiplied by the scale to get the real world value.