Difference between revisions of "PWM"

Revision as of 00:01, 9 April 2007

On this page, you will find usefull informations to configure and use the Pulse Width Modulation (PWM) capabilities of your APF9328 board.

Your is capable of driving 2 PWM signals:

• one is linked to the LCD controller and allow to control LCD backlight, see LCD page for more informations
• the other can be used to generate PWM signals in several mode:

* audio playback
* real PWM

Configuration

First be sure to have the PWM Linux driver activated:

$ make linux-menuconfig

File:PWMconfig.png

$ make

Installation

Either copy generated module target/linux/modules/pwm/pwm.ko to your system with TFTP or NFS or reflash the generated rootfs

Usage

Load the module:

# insmod /lib/modules/2.6.18.1/extra/pwm/pwm.ko

or (if you have reflashed your rootfs):

# modprobe pwm

PWM Mode

Remark:

• The pwm has a resolution of 1uS

Now you have access to /sys/class/pwm/ functionnalities:

• to activate PWM:

# echo 1 > /sys/class/pwm/pwm0/active

• to de-activate PWM:

# echo 0 > /sys/class/pwm/pwm0/active

• to change frequency (for example 500 Hz):

# echo 500 > /sys/class/pwm/pwm0/frequency

• to change period (for example 100us):

# echo 100 > /sys/class/pwm/pwm0/period

• to change duty cycle (for example 50.0%)

# echo 500 > /sys/class/pwm/pwm0/duty

Audio Mode

Audio playback mode is not fully functionnal/tested yet. Ask JulienB if you really need it...

Links

• SoX, sound format converter
• http://en.wikipedia.org/wiki/Pulse-width_modulation