Linux Device Drivers Development

Using PWMs with the sysfs interface

The PWM core sysfs root path is /sys/class/pwm/. It is the user space way to manage PWM devices. Each PWM controller/chip added to the system creates a pwmchipN directory entry under the sysfs root path, where N is the base of the PWM chip. The directory contains the following files:

• npwm: This is a read-only file, printing the number of PWM channels that the chip supports
• Export: This is a write-only file, allowing you to export a PWM channel for use with sysfs (this functionality is equivalent to the GPIO sysfs interface)
• Unexport: This unexports a PWM channel from sysfs (write-only)

The PWM channels are numbered using an index from 0 to pwm<n-1>. These numbers are local to the chip. Each PWM channel ...