I've managed to create a dtbo for pwm that doesn't make the system barf at
me. It shows up properly when I cat slots and I can see the pin assignments
in pins. I'm not really understanding what the file does and what I can
find for documentation on writing dts files never seems to resemble any of
the overlays on the bone.
The first one I wrote I basically hacked up another file that enabled a
single pwm ( ehrpwm2A) so I tried to make it work for ehrpwm0A and
ehrpwm0B. I ended up with this
/dts-v1/;
/plugin/;
/{
compatible = "ti,beaglebone", "ti,beaglebone-black",
"ti,beaglebone-green";
part-number = "PDM-PWM0";
version = "00A0";
exclusive-use =
/* PINS */
"P9.29",
"P9.31",
/* devices */
"ehrpwm0A",
"ehrpwm0B";
fragment@0 {
target = <&am33xx_pinmux>;
__overlay__ {
pinctrl_spec: Panel_Pins {
pinctrl-single,pins = <
0x190 0x03 /* P9_29 MODE3 ehrpwm0A PWM */
0x194 0x03 /* P9_31 MODE3 ehrpwm0B PWM */
>;
};
};
};
fragment@1 {
target = <&ocp>;
__overlay__ {
test_helper: helper {
compatible = "bone-pinmux-helper";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_spec>;
status = "okay";
};
};
};
fragment@2 {
target = <&epwmss0>;
__overlay__ {
status = "okay";
};
};
fragment@3 {
target = <&ehrpwm0>;
__overlay__ {
status = "okay";
};
};
};
Like I said, it seems to load OK and /sys/class/pwm shows pwmchip0 but I
don't have anything to actually test the PWM with at the moment. Does this
look correct?
The exclusive_use part is pretty obvious.
I'm wondering if the names defined by lines like "pinctrl_spec: Panel_Pins"
are pre-defined secret codes required to make things work or if they're
just arbitrary labels assigned by the person creating the file?
In fragment one there's "test_helper: helper" which looks like an arbitrary
label - but is it?
I would think that in "target = <whatever>" the "whatever" has to be the
proper name/device/whatever it is (like tscadc for analog inputs).
Then one other thing. I copied this file, renamed it PDM-PWM1-00A0.dts,
changed the partno, defined pins, etc to be ehrpwm1
/dts-v1/;
/plugin/;
/{
compatible = "ti,beaglebone", "ti,beaglebone-black",
"ti,beaglebone-green";
part-number = "PDM-PWM1";
version = "00A0";
exclusive-use =
/* PINS */
"P8.36",
"P8.34",
/* devices */
"ehrpwm1A",
"ehrpwm1B";
fragment@0 {
target = <&am33xx_pinmux>;
__overlay__ {
pinctrl_spec: Panel_Pins {
pinctrl-single,pins = <
0x0C8 0x02 /* P8_36 MODE3 ehrpwm1A PWM */
0x0CC 0x02 /* P9_34 MODE3 ehrpwm1B PWM */
>;
};
};
};
fragment@1 {
target = <&ocp>;
__overlay__ {
test_helper: helper {
compatible = "bone-pinmux-helper";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_spec>;
status = "okay";
};
};
};
fragment@2 {
target = <&epwmss1>;
__overlay__ {
status = "okay";
};
};
fragment@3 {
target = <&ehrpwm1>;
__overlay__ {
status = "okay";
};
};
};
and it seems to behave, I get pwmchip2 in /sys/class/pwm and it shows up in
slots but in pins only the first file's pins are shown as assigned.
I don't know if the name Panel_Pins can't be the same in the two files or
if maybe fragment 1's "pinctrl-0" needs to have a different number or
what...
Any enlightenment and guidance would be massivly appreciated.
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