I've been looking around for quite a number of days now and while there is
quite a lot of information on the subject, most of it appears to be
outdated and/or insufficient for my system. I have a BBB Rev C running the
default Debian (uname -r returns "kernel 8.13-bone70"). I have tried a few
guides step by step to no avail
(https://briancode.wordpress.com/2015/01/06/working-with-pwm-on-a-beaglebone-black/,
http://hipstercircuits.com/enable-pwm-on-beaglebone-with-device-tree-overlays/)
Basing my attempts off of these and Derek Molloy's tutorial on GPIO with
Device Tree Overlays (which work just fine), this is my .dts file
> /* Simple PWM overlay */
>
> /dts-v1/;
> /plugin/;
>
> / {
> compatible = "ti,beaglebone", "ti,beaglebone-black";
>
> /* identification */
> part-number = "SJP-PWM";
> version = "00A0";
>
> /* state the resources this cape uses */
> exclusive-use =
> "P9.21",
> "P9.22",
>
> "ehrpwm0A",
> "ehrpwm0B";
>
> fragment@0 {
> target = <&am33xx_pinmux>;
> __overlay__ {
> bb_ehrpwm0_pins: pinmux_bb_ehrpwm0_pins {
> pinctrl-single,pins = <
> 0x154 0x03 /* P9_21 muxRegOffset, Mode3 (ehrpwm0B) */
> 0x150 0x03 /* P9_22
> muxRegOffset, Mode3 (ehrpwm0A) */
> >;
> };
> };
> };
> /************************/
> /* Pin Multiplexing */
> /************************/
>
> fragment@1 {
> target = <&ocp>;
> __overlay__ {
> P9_21_pinmux {
> compatible = "bone-pinmux-helper";
> pinctrl-names = "default";
> pinctrl-0 = <&bb_ehrpwm0_pins>;
> status = "okay";
> };
> };
> };
>
> /**************************/
> /* Enable PWM Devices */
> /**************************/
>
> fragment@2 {
> target = <&epwmss0>;
> __overlay__ {
> status = "okay";
> };
> };
>
> fragment@3 {
> target = <&ehrpwm0>;
> __overlay__ {
> status = "okay";
> };
> };
> };
>
When I compile and load the overlay, the pwmchip0 directory appears in
/sys/class/pwm much as I expected. I can also
sudo sh -c "echo 1 > /sys/class/pwm/export" to get the pwm1 directory
(which should correspond to ehrpwm0a on pin P9_22, right?)
This is as far as I get however, as no combination of setting period_ns,
duty_ns and run produces any output. What am I missing?
Thanks,
Stefan
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