A simple character device driver for reading a Bosch BMP180 sensor module
- http://derekmolloy.ie/writing-a-linux-kernel-module-part-2-a-character-device
- https://github.com/akoskovacs/kmod_example
- https://elinux.org/Interfacing_with_I2C_Devices#Beagleboard_I2C2_Enable
- https://beagleboard.org/static/BBxMSRM_latest.pdf
- https://cdn-shop.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf
- https://www.howtoforge.com/reading-files-from-the-linux-kernel-space-module-driver-fedora-14
The IIO bmp280 driver in mainline linux exposes the sensor readouts to sysfs.
The main expansion header on the BB-xM exposes the I2C2 interface. The others (total 4) are used by various connectors; HDMI, Camera, etc.
| Pin# | Description | BMP180 pin |
|---|---|---|
| 1 | VIO_1V8 | VIN |
| 23 | I2C2_SDA | SDA |
| 24 | I2C2_SCL | SCL |
| 28 | GND | GND |
The I2C2 interface shows up as /dev/i2c-1. This bus can be probed for devices with i2cdetect:
$ i2cdetect -r 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77
The BMP180's slave address is "0xEF (read) and 0xEE (write)" according to it's datasheet. Without the R/W bit that leaves 0x77.
Tell the kernel the device at this address is a BMP180 sensor:
$ echo "bmp180 0x77" | sudo tee /sys/bus/i2c/devices/i2c-1/new_device
The drivers will be loaded automagically:
$ lsmod|grep bmp
bmp280_i2c 16384 0
bmp280 20480 1 bmp280_i2c
Read the data:
$ cat /sys/bus/i2c/devices/1-0077/iio\:device1/in_*_input
101.463000000
23700
This requires the bmp280 driver is loaded and /sys/bus/i2c/devices/1-0077/iio\:device1/in_*_input is available.
$ git clone https://github.com/pgils/IITE-DRVO.git
$ cd IITE-DRVO
$ make insert
$ echo "pressure"|sudo tee /dev/drvoscd
$ sudo cat /dev/drvoscd
101.792000000
Compile the drvoscd driver for IITE-LINUX-xM
$ cd linux-stable
$ git apply ../IITE-DRVO/patches/0001-dts-omap-beagle-xm-map-bmp180-to-I2C2.patch
$ make ARCH=${CLFS_ARCH} CROSS_COMPILE=${CLFS_TARGET}- \
INSTALL_MOD_PATH=${CLFS}/targetfs modules_install
$ git clone https://github.com/pgils/IITE-DRVO.git
$ cd IITE-DRVO
$ make ARCH=${CLFS_ARCH} CROSS_COMPILE=${CLFS_TARGET}- \
INSTALL_MOD_PATH=${CLFS_TARGET_FS} \
-C ${CLFS_TARGET_FS}/lib/modules/5.6.12/build \
M=$PWD modules_install
$ cp arch/arm/boot/{zImage,dts/omap3-beagle-xm.dtb} ${CLFS_TARGET_FS}/boot/