AM335x Starter Kit board SDK8.0 PWM problem

xin Ryan

Dear All,
Stdudy SDK8.0 on AM335x Starter Kit board, download SDK8.0 and creat SD system
Debug PWM module follow TI AM335X WIKI:
I want to modify PWM module Attribute(Period, Duty and so on)

root@am335x-evm:~# uname -r
3.14.26-g2489c02
root@am335x-evm:~# ls /sys/class/pwm/pwmchip0
device export npwm power subsystem uevent unexport
root@am335x-evm:~# echo 0 >/sys/class/pwm/pwmchip0/export
-sh: echo: write error: Device or resource busy

I don't know whether to modify the kernel code?

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Ryan,

Check this wiki: http://processors.wiki.ti.com/index.php/Linux_Core_PWM_User's_Guide

0 xin Ryan over 10 years ago in reply to Biser Gatchev-XID

Expert 1140 points

Hi
I am in accordance with the Link operation.
Do not agree with the WIKI description.
Board is AM335x Starter Kit, SDK8.0 download TI website

0 Yordan Kovachev over 10 years ago in reply to xin Ryan

TI__Guru**** 161600 points

Hi Ryan,

I encountered the same problem, when trying to write in /sys/class/pwm/pwmchip0/export.

You need to enable your PWM driver & rebuild your kernel.

You can do that either with menuconfig, as shown in the wiki, or by adding:
CONFIG_PWM=y
CONFIG_PWM_SYSFS=y
CONFIG_PWM_TIECAP=y
CONFIG_PWM_TIPWMSS=y
in your .config file.

Then the commands:
echo 0 > /sys/class/pwm/pwmchip0/export
echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable
will work.

Best Regards,
Yordan

0 xin Ryan over 10 years ago in reply to Yordan Kovachev

Expert 1140 points

Hi,

Thank your help

Do you debug on SDK8.0?

But I study SDK8.0 under Starter Kit board

Build Kernel configure file use the singlecore-omap2plus_defconfig

I found the confiure file is opened:

Debugging

0 xin Ryan over 10 years ago in reply to xin Ryan

Expert 1140 points

Add configure;

3686 CONFIG_PWM=y
3687 CONFIG_PWM_SYSFS=y
3688 # CONFIG_PWM_PCA9685 is not set
3689 CONFIG_PWM_TIECAP=y
3690 CONFIG_PWM_TIEHRPWM=y
3691 CONFIG_PWM_TIPWMSS=y

0 Yordan Kovachev over 10 years ago in reply to xin Ryan

TI__Guru**** 161600 points

Yes, I work on AM335x Starter Kit, running SDK8.0 (kernel 3.14.26).
I used menuconfig to enable the PWM driver.

Best Regards,
Yordan

0 xin Ryan over 10 years ago in reply to Yordan Kovachev

Expert 1140 points

Hi,
   The problem is found, but maybe study
   1.Our BSP is SDK8.0, so use the same defconfig file
   2.My board is indeed Starter Kit
   3. Now the Class node is haved, but I modify the code(linux-3.14.26/drivers/pwm/core.c)
   root@am335x-evm:~# echo 0 >/sys/class/pwm/pwmchip0/export
   -sh: echo: write error: Device or resource busy
   pwm_export_store() ----> pwm_request_from_chip() ------->pwm_device_request()
   if (test_bit(PWMF_REQUESTED, &pwm->flags))
return -EBUSY;
The last, I mask the code
Now, function is OK, but I don't known the root case.

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AM335x Starter Kit board SDK8.0 PWM problem