Hi,
In case someone still needs a solution to this problem, I've written a
small kernel patch: ti_ehr_pwm.patch
<https://sites.google.com/site/avterekhov/ti_ehr_pwm.patch> and a short
description of how to apply it:
https://randomlinuxhacks.wordpress.com/2014/09/16/changing-pwm-period-on-beaglebone-black/
So far it works for me.
On Thursday, June 26, 2014 8:10:26 AM UTC+2, jmc...@gmail.com wrote:
>
> I also tried this and had no luck :-/
>
> PWM on the BBB is turning out to be more work than I had thought.
>
> On Monday, January 6, 2014 12:13:37 PM UTC-8, Anto Dominic wrote:
>>
>> Thanks,
>>
>> Tried your trick.... even replaced the new dtbo file.... but even after
>> that I am getting the default value for Period ( ie, 5000000) and duty (ie,
>> 0) ... Is there any step that you missed in between...??. Anyways thanks
>> for the tip..:)
>>
>> On Monday, 8 July 2013 08:44:54 UTC+5:30, tohr...@gmail.com wrote:
>>>
>>> Hello,
>>>
>>> you can change period by changing dtbo files.
>>>
>>> 1 Generate dts file from original dtbo file
>>> dtc -I dtb -O dts -o /lib/firmware/bone_pwm_P8_13-00A0.dts /lib/firmware
>>> /bone_pwm_P8_13-00A0.dtbo
>>>
>>> 2 Change period
>>> open file "/lib/firmware/bone_pwm_P8_13-00A0.dts" with editor at
>>> lines around line 26:
>>> pwm_test_P8_13 {
>>> compatible = "pwm_test";
>>> pwms = <0xdeadbeef 0x1 0x7a120 0x1>;
>>>
>>> and change to following, for example change period to 100000ns=0.1ms
>>>
>>> pwm_test_P8_13 {
>>> compatible = "pwm_test";
>>> pwms = <0xdeadbeef 0x1 100000 0x1>;
>>>
>>> where
>>> -3rd parameter of line"pwms = ~" is period.
>>> -period (and other parameters) can be written in either decimal or
>>> hexadecimal of 0xABC format.
>>> -default period 0x7a120 is 5000000 in decimal.
>>> -As you mentioned, Both A and B output for one eHRPWM must have same
>>> period setting.
>>> If not, the second device will fail to setup at "echo (device)>
>>> /sys/devices/bone_capemgr.*/slots" command.
>>>
>>> 3 Compile to new dtbo file
>>> dtc -O dtb -o bone_pwm_P8_13-00A0.dtbo -b 0 -@ bone_pwm_P8_13-00A0.dts
>>>
>>> You'd better back up original dtbo file before overwriting it.
>>>
>>> 4 Use new dtbo file.
>>> echo bone_pwm_P8_13 > /sys/devices/bone_capemgr.*/slots
>>>
>>>
>>>
>>> 2013年6月4日火曜日 16時33分00秒 UTC+9 sultanof.ilo...@gmail.com:
>>>>
>>>> Hey,
>>>> yes sure, duty must be (0 <= duty <= period). Otherwise you would try
>>>> to to set a pwm duty cycle of less than 0% or more than 100%. Returning an
>>>> error to the user is a proper way to handle this.
>>>>
>>>> As mentioned above EHRPWM1 and EHRPWM2 share the same base period (or
>>>> respectively the base frequency). If I enable both PWM ouputs, writing to
>>>> the period files always results in an error. Enabeling only one of the two
>>>> outputs lets me change the periods.
>>>> This does make sense after all. I assume the necessary crosschecking of
>>>> the conditions (0 <= duty <= period) for related PWM outputs is simply not
>>>> implemented yet or mayby just faulty.
>>>>
>>>> Am Montag, 3. Juni 2013 12:25:15 UTC+2 schrieb lawe...@gmail.com:
>>>>>
>>>>> Hi
>>>>>
>>>>> I'm just starting out, but here is what I found. Hopefully it can help
>>>>> you.
>>>>> The period must be greater than duty.
>>>>> This worked fine for me:
>>>>> echo 100000 > /sys/devices/ocp.2/pwm_test_P9_14.12/period
>>>>> Period is given in ns. Duty is given in ns on/off depending on
>>>>> polarity.
>>>>>
>>>>
>>>
--
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