I see someone has recently asked a question on this old post.
Controlling pwm using linux is nicely documented in kernel docs:
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-pwm
controlling simple servo takes period 20 ms and duty_cycle 1 - 2 ms, start
with these values
echo 20000000 > /sys/class/pwm/pwmchip[num]/pwm[num]/period
... rest is up to you
As for the 'howto' described by Tekuconcept in previous reply, I wouldn't
bother about modifying dtb files anymore:
-Upgrade kernel to 4.1 (since this post is originally about the 3.14 kernel)
--- add 'deb [arch=armhf] http://repos.rcn-ee.com/ubuntu trusty main'
to apt sources (modify to own needs), install new linux-image.
--- modify /boot/uEnv.txt or /boot/uboot/uEnv.txt so the new kernel is
loaded, I mixed up my original uEnv and the suggestions from:
https://eewiki.net/display/linuxonarm/BeagleBone+Black#BeagleBoneBlack-DealingwitholdBootloaderineMMC
--- dont screw up uEnv... (manual loading of kernel image in memory
using uboot console is possible with serial debugger but painfull...)
-clone 'bb-overlays' github repo and install
-clone 'universal-io' github repo and install
-reboot (took me an hour to figure this one out...)
Now you can 'config-pin overlay cape-universaln', 'config-pin P[num] pwm'.
(all in user space)
That's about it, works flawless. (took me a couple of days to figure
everything out though, as hobbyist it's fishing for the correct info on the
web...)
kind regards,
Dieter
On Wednesday, July 15, 2015 at 1:46:00 PM UTC+2, rod0...@gmail.com wrote:
>
> after doing so how do you control duty cycle, period...?
>
> On Thursday, April 16, 2015 at 7:29:59 AM UTC-6, TekuConcept wrote:
>>
>>
>> - config-pin [pin] [state] will mux the pins to the PWM Subsystems
>> - Modifying am33xx.dtsi under the dtb-rebuilder project such that:
>> epwmss0, epwmss1, and epwmss2 status = "okay", and their children,
>> ehrpwm0,
>> ehrpwm1, and erhpwm2 status = "okay", will enable the system clocks for
>> each subsystem. This equivalent to setting the following registers to the
>> given values in their respective order:
>>
>> reg[0x44E00000] = 0x0 *# CM_PER_L4L3_CLKSTCTRL.CLKTRCTRL = NO_SLEEP*
>> reg[0x44E000D4] = 0x2* # CM_PER_EPWMSS0_CLKCTRL.MODULEMODE = ENABLE*
>> reg[0x44E000CC] = 0x2 *# CM_PER_EPWMSS1_CLKCTRL.MODULEMODE = ENABLE*
>> reg[0x44E000D8] = 0x2* # CM_PER_EPWMSS2_CLKCTRL.MODULEMODE = ENABLE*
>>
>> - However, after all this, the PWM subsystems will still not work
>> because the Time Based Clocks are not enabled. To enable them, one would
>> need kernel elevated privileges: such as modifying the register through a
>> simple kernel module.
>>
>> reg[0x44E10664] = 0x7 # CONTROL_MODULE.pwmss_ctrl = pwmss0_tbclken |
>> (pwmss1_tbclken << 1) | (pwmss2_tbclken << 2)
>>
>> Using a simple kernel module I built for hardware debugging, I was able
>> to confirmed this. (Look at ioremap & iounmap under kernel module
>> development)
>>
>
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