pwm via /sys/class/pwm/pwm0

[sandstein]

Hi

I have just enabled the pwm with "dtoverlay=pwm-2chan" in the config.txt on raspbian with a 4.1.7-v7+ kernel.

It gives me a nice directory /sys/class/pwm/pwmchip0 after exporting channel 0 via a "echo 0 > export"
No i have set up the pwm:
cd pwm0
echo 20000000 > period
echo 1000000 > duty_cycle
echo 1 > enable

But unfortunatly i can not see anything on output gpio18 checked with an oszilloscope. I think i read somewhere
that i need to play sound once to get the clock enabled for pwm but also starting aplay does not change anything.
My question now is what am i missing to get working hw pwm output?

Thanks
Tim

[joan]

I don't know.

However there are alternative methods to start PWM on the hardware channels, e.g. http://abyz.co.uk/rpi/pigpio/pigs.html#HP

[fsr]

what am i missing to get working hw pwm output?

This works for me on a rPi2 running Jessie:

Code: Select all

speaker-test -Dhw:CARD=ALSA,DEV=0 -f300 -c1 -p100 -P2 -l1 > /dev/null 2>&1

[mishal]

In order to avoid pinmux conflict one must either use audio DT-overlay or pwm DT-overlay.
so the first step is to comment dtparam=audio=on
Second - is to switch clock to pwm. How? I don't know.