I am using the ehrpwm2A PWM on P8_19. Usage of this requires the following
device tree overlay (BB-PWM2-00A0.dts):
/dts-v1/;
/plugin/;
/{
compatible = "ti,beaglebone", "ti,beaglebone-black";
part-number = "BB-PWM2";
version = "00A0";
fragment@0 {
target = <&am33xx_pinmux>;
__overlay__ {
pinctrl_spec: Panel_Pins {
pinctrl-single,pins = <
0x020 0x04 /* P8_19 MODE4 ehrpwm2A 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 = <&epwmss2>;
__overlay__ {
status = "okay";
};
};
fragment@3 {
target = <&ehrpwm2>;
__overlay__ {
status = "okay";
};
};
};
In the above device tree overlay, fragment 0 configures P8_19 to be the
output of PWM2A (instead of a GPIO or other function), and fragments 1, 2,
and 3 enable the needed on-chip peripherals. 'ocp' is on-chip-peripherals,
'epwmss' is PWM sub-system, and 'ehrpwm2' is PWM2.
Compile this overlay using:
dtc -O dtb -o BB-PWM2-00A0.dtbo -b 0 -@ BB-PWM2-00A0.dts
Copy to /lib/firmware:
sudo cp BB-PWM2-00A0.dtbo /lib/firmware
At this point, get to root:
sudo su
Load the device tree overlay (this must be done logged in as root, sudo
won't work – I think because of the redirect). Note that this path is
different than the earlier kernels due to a redesign of the cape manager:
root@arm:/home/ubuntu# echo BB-PWM >
/sys/devices/platform/bone_capemgr/slots
Check that overlay was loaded:
root@arm:/home/ubuntu# cat /sys/devices/platform/bone_capemgr/slots
0: PF---- -1
1: PF---- -1
2: PF---- -1
3: PF---- -1
4: P-O-L- 0 Override Board Name,00A0,Override Manuf,BB-PWM2
Check that the pin is configured to output the PWM2A:
root@arm:/home/ubuntu# cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins |
grep 0820
pin 8 (44e10820.0) 00000004 pinctrl-single
You need to see the pinmux at offset $820 have mode 4. If it is not 4,
your PWM may be working fine, but you won't see the signal on pin P8_19.
You should also see pwmchip0 appear at /sys/class/pwm:
root@arm:/home/ubuntu# ls /sys/class/pwm
pwmchip0
Change to pwmchip0 folder:
root@arm:/home/ubuntu# cd /sys/class/pwm/pwmchip0
Export the PWM to userspace:
root@arm:/sys/class/pwm/pwmchip0# echo 0 > export
You should now see a pwm0 folder:
root@arm:/sys/class/pwm/pwmchip0# ls
device export npwm power pwm0 subsystem uevent unexport
Change to the pwm0 folder, configure the PWM and enable it:
root@arm:/sys/class/pwm/pwmchip0/pwm0# ls
duty_cycle enable period polarity power uevent
root@arm:/sys/class/pwm/pwmchip0/pwm0# echo 1000000 > period
root@arm:/sys/class/pwm/pwmchip0/pwm0# echo 250000 > duty_cycle
root@arm:/sys/class/pwm/pwmchip0/pwm0# echo 1 > enable
I think the units of period and duty_cycle are both nanoseconds (not
confirmed with a scope). duty_cycle is not a percentage, so these setting
are running the PWM at 1kHz, 25% duty cycle.
Hope this helps!
On Wed, Sep 30, 2015 at 9:53 AM, Kevin Ault <[email protected]> wrote:
> I have the PWM working perfectly on the 4.1 kernel, and I am planning to
> post the solution to this thread within a few days.
>
> On Wed, Sep 30, 2015 at 12:36 AM, Khanh Nguyen <[email protected]>
> wrote:
>
>> No, I haven't been able to get kernel 4.1 and PWM working. I haven't
>> looked at the link you included either. I'll definitely take a look over
>> the weekend. Hey, can you send me the link to this post on google group? I
>> can't seem to find my post...
>>
>> Thanks,
>> Khanh
>>
>> On Sun, Sep 27, 2015 at 4:08 PM, <[email protected]> wrote:
>>
>>>
>>> Khanh,
>>>
>>> Have you got the PWMs working yet? This documentation (
>>> http://processors.wiki.ti.com/index.php/Linux_Core_PWM_User's_Guide)
>>> most closely matches what I am seeing under the 4.1 kernel, but I had to
>>> fall back on these same old overlays to even see the PWMs. Seem to able to
>>> export, configure, and enable the PWM, but I'm just not seeing anything on
>>> the output pin.
>>>
>>> -Kevin
>>>
>>>
>>> On Wednesday, September 9, 2015 at 3:20:19 AM UTC-5, Khanh Nguyen wrote:
>>>>
>>>> Hey guys, I'm working on a project where as I was using the
>>>> ocp.X/bone_pwm_P9_11 and such in kernel 3.8. I just recently updated my
>>>> Beaglebone black to kernel 4.1 and couldn't get PWM to work...
>>>>
>>>> I was trying to use dtc, rebuild the device tree overlay. I pulled the
>>>> old am33xx_pwm from
>>>> https://github.com/beagleboard/devicetree-source/blob/master/arch/arm/boot/dts/am33xx_pwm-00A0.dts
>>>> and some of these bad boys bone_pwm_PX_YZ from
>>>> https://github.com/beagleboard/devicetree-source/blob/master/arch/arm/boot/dts/bone_pwm_P8_13-00A0.dts.
>>>> I know that these are pretty old, but was just thinking maybe it would work
>>>> with the new kernel?
>>>>
>>>> Then I was able to build these device tree overlays and load them into
>>>> the /boot/uEnv.txt. However, when I went to /sys/devices/platform, I only
>>>> saw ocp:pwm and it's nothing like the old kernel 3.8 where you'd have duty,
>>>> period, and all that good stuff. Is this the right way to access PWM or I
>>>> had to use the example in the Bacon device tree overlay? If so, is there a
>>>> document on how to know which PWM pin to export?
>>>>
>>>> I've been playing with this new kernel for quite a while now and still
>>>> haven't got any luck. Any advice or pointers will be greatly appreciated.
>>>>
>>>> Thanks
>>>>
>>>> --
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