PWM is enabled but no voltage is observed


I have a following issue with BBB PWM. It seems to be fully operational from software point but I observe no voltage on voltmeter. It shows like 0,11 V and no changes at all when I change duty.

On BBB I have installed recent Arch Linux and did following:

echo am33xx_pwm > /sys/devices/bone_capemgr.8/slots

echo bone_pwm_P8_13 > /sys/devices/bone_capemgr.8/slots

echo 0 > export

after I got following files:

ls /sys/class/pwm/pwm0

device duty_ns period_ns polarity power run subsystem uevent

and applied

echo 1000000 > period_ns

echo 250000 > duty_ns

echo 1 > run

and got 0,11V, changing duty_ns has l can’t get even more them 1V. But I expected 3,3V with period 1000000 and duty 100000.

[root@alarm pwm0]# cat /sys/kernel/debug/pwm

platform/48304100.ecap, 1 PWM device

pwm-0 ((null) ):

platform/48304200.ehrpwm, 2 PWM devices

pwm-0 ((null) ):

pwm-1 ((null) ):

platform/48302200.ehrpwm, 2 PWM devices

pwm-0 ((null) ):

pwm-1 ((null) ):

platform/48300100.ecap, 1 PWM device

pwm-0 ((null) ):

What could be the issue?
Thank you.

Have you tried

modprobe pwm_test

on your console? I guess after that you can see voltage on oscilloscope, otherwise you are missing pwm_test.ko in /lib/modules/<uname -r>/kernel/drivers/pwm/ folder.