PWM
On this page, you will find usefull informations to configure and use the Pulse Width Modulation (PWM) capabilities of your APF9328 board.
Your board is capable of driving 2 PWM signals:
- one is linked to the LCD controller and allow to control the LCD backlight
- the other can be used to generate a PWM signal in several mode:
- audio playback
- real PWM
Configuration
First be sure to have the PWM Linux driver activated:
$ make linux26-menuconfig
And in Device Drivers ---> Armadeus specific drivers choose:
Then rebuild your system:
$ 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/2.6.23.1/extra/pwm/pwm.ko
or (if you have reflashed your rootfs):
# modprobe pwm
- Create device file if not existing (Major is dynamically allocated)
# DEV=`cat /proc/devices | grep imx-pwm | cut -d " " -f 1`; mknod /dev/pwm c $DEV 0
PWM Mode
Remark:
- The pwm has a resolution of 1uS
Now you have access to /sys/class/pwm/ functionnalities:
- to activate PWM:
# echo 1 > /sys/class/pwm/pwm0/active
- to de-activate PWM:
# echo 0 > /sys/class/pwm/pwm0/active
- to change frequency (for example 500 Hz):
# echo 500 > /sys/class/pwm/pwm0/frequency
- to change period (for example 100us):
# echo 100 > /sys/class/pwm/pwm0/period
- to change duty cycle (for example 50.0%)
# echo 500 > /sys/class/pwm/pwm0/duty
Audio Mode
Audio playback mode is working since v0.5 of PWM driver (thanks to SebastienR). You can play 8, 16 & 32 KHz 8bit linear RAW sound. It's recommended to play 8kHz one, as they use less CPU ressources. To convert a sound to the right format we recommend to use SoX (on Linux). For exemple:
[host]$ sox /usr/share/sounds/KDE_Chimes_1.ogg -r 8192 -b -u -c 1 Chimes.raw -r -> sampling rate -b -> byte/8bit signal -u -> linear /not compressed -c 1 -> Mono / 1 channel
Then you can test it using target/linux/modules/pwm/test/testplaymode:
[host:/.../armadeus]$ make -C target/linux/modules/pwm/test/ [host:/.../armadeus]$ cp target/linux/modules/pwm/test/testplaymode $NFS_DIR [host:/.../armadeus]$ cp target/linux/modules/pwm/test/KDE_Startup_2.raw $NFS_DIR
on target do:
# testplaymode
or
# testplaymode KDE_Startup_2.raw
