How to write applications which use our drivers ----------------------------------------------- You have several choices in accessing sensor devices using the drivers in our package. This document will briefly describe these methods, their advantages and disadvantages, and provide examples. From lowest-level to the highest-level, the access methods are: 1) Character device access to the i2c bus driver via /dev/i2c-x 2) I2C bus access functions as defined in kernel/include/i2c-dev.h 3A) /proc access to the chip device driver 3B) sysfs access to the chip device driver 4) libsensors library 5) sensors program Details: 1. Direct /dev access using ioctls ---------------------------------- Character device access to the i2c bus driver via ioctls on a /dev device. This device could be i2cx, i2c-x, or i2c/x, where x is an integer. The ioctls are defined in doc/dev-interface in the i2c package or Documentation/i2c/dev-interface in the linux kernel sources. This method does not use a chip device driver at all. However it does require the i2c-dev module. The driver must set an individual chip address on the bus via an ioctl, so it must use locking if multiple devices on the bus are being accessed. No access is provided for non-i2c busses such as ISA. For good examples, see prog/detect/i2cdetect.c and prog/detect/sensors-detect. 2. Direct /dev access using inline functions -------------------------------------------- I2C bus access inline functions as defined in kernel/include/i2c-dev.h, and in doc/dev-interface in the i2c package or Documentation/i2c/dev-interface in the linux kernel sources. Note that these used to be defined in in the kernel source tree. However, userspace applications are not supposed to include kernel headers, so the inline functions were removed from the kernel file in recent kernels. Use the header file in this package instead. This method does not use a chip device driver at all. However it does require the i2c-dev module. The driver must set an individual chip address on the bus via an ioctl, so it must use locking if multiple devices on the bus are being accessed. No access is provided for non-i2c busses such as ISA. For good examples, see prog/detect/i2cdetect.c, prog/dump/i2cdump.c, and prog/dump/i2cset.c. 3A. /proc access (2.4 kernels) ----------------------------- Chip drivers using the i2c-proc module create subdirectories in /proc/sys/dev/sensors which can be accessed directly by applications. Naming and content standards for the entries in these subdirectories is documented in the file doc/developers/proc. Note that these standards may not be strictly followed. If a new driver adheres to these standards then an application may be able to support new devices on-the-fly. /proc access provides a method to read and write sensor values for any driver using i2c-proc, including ISA chip drivers. This method also works well for shell and perl scripts written to access a specific device. Note that i2c-proc is standard in the kernel as of kernel 2.4.13. Note that most drivers provide only raw sensor readings via /proc; many readings must be scaled or adjusted, and these adjustments must often be changed by the user. An application using /proc must generally provide adjustment facilities and the requirements of the adjustments can be quite complex. If you need adjustment facilities, consider the libsensors library, below. For examples of programs using /proc accesses, see prog/eeprom/decode-dimms.pl, prog/matorb/displayit.pl, prog/maxilife/writelcd.sh, prog/rrd/sens_update_rrd, prog/pwm/fancontrol, and prog/pwm/pwmconfig. Also search freshmeat for sensors applications. 3B. sysfs access (2.6 kernels) ------------------------------ Chip drivers using the i2c-sensor module create subdirectories in the sysfs filesystem (usually /sys) which can be accessed directly by applications. Naming and content standards for the entries in these subdirectories is documented in the file Documentation/i2c/sysfs-interface in the 2.6 kernel source tree. Note that these standards may not be strictly followed. If a new driver adheres to these standards then an application may be able to support new devices on-the-fly. sysfs access provides a method to read and write sensor values for any driver using i2c-sensor, including ISA chip drivers. This method may also works well for shell and perl scripts written to access a specific device. Note that sysfs is standard in 2.6 kernels. Note that most drivers provide only raw sensor readings via /sys; many readings must be scaled or adjusted, and these adjustments must often be changed by the user. An application using /proc must generally provide adjustment facilities and the requirements of the adjustments can be quite complex. If you need adjustment facilities, consider the libsensors library, below. For an examples of a program using /sys accesses, see gkrellm. See also lib/proc.c and prog/dump/i2cbusses.c for examples. The sysfsutils package may also be helpful. Also search freshmeat for sensors and sysfs applications. 4. libsensors library --------------------- The libsensors library provides standardized access to all chip drivers. It also provides a translation layer with settings in /etc/sensors.conf so that your application sees adjusted (scaled) values using settings provided by the user. Other facilities are sensor renaming, limit setting, and ignoring individual sensors. The libsensors library supports both 2.4 and 2.6 kernels. Unfortunately there is little documentation for libsensors. See the 'sensors' application in prog/sensors for an example. The source for libsensors is in the lib/ directory. Another example is in prog/sensord. Also search freshmeat for sensors applications. One other limitation of libsensors is that it is relatively cumbersome to add support for new devices. Note that libsensors falls under the GPL, not the LGPL. In more human language, that means it is FORBIDDEN to link any application to the library, even to the shared version, if the application itself does not fall under the GPL. This may or may not be changed in the future. Contact us if you wish to discuss your application. For an examples of a program using libsensors accesses, see prog/sensors/sensors. Also search freshmeat for sensors applications. 5. sensors program ------------------ The 'sensors' program is a text-based application that uses libsensors. The output is fairly standardized; therefore this output could be used by other applications. One simple method is 'sensors|grep ALARM'.