ehrpwm period fails to be changed

Mike Worster

I'm seeing an issue with updating the PWM period via the serial console. When I go to write a period via the sysfs I get an invalid argument error.

As I understand it, each PWM chip must have the same value for period for each submodule (ie PWMchip1:pwm0 and PWMchip1:pwm1 must have matching periods). However I'm trying to understand the nuances of setting this via the sysfs entries:

It's clear that even if both are disabled and have a 0 duty cycle, the periods can't be changed:

[root /sys/class/pwm/pwmchip1]# cat pwm0/enable
0
[root /sys/class/pwm/pwmchip1]# cat pwm1/enable
0
[root /sys/class/pwm/pwmchip1]# cat pwm0/duty_cycle
0
[root /sys/class/pwm/pwmchip1]# cat pwm1/duty_cycle
0
[root /sys/class/pwm/pwmchip1]# cat pwm0/period
50000
[root /sys/class/pwm/pwmchip1]# cat pwm1/period
50000
[root /sys/class/pwm/pwmchip1]# echo 60000 > pwm0/period
[  202.183000] ehrpwm 48300200.ehrpwm: Period value conflicts with channel 1
-sh: echo: write error: Invalid argument
[root /sys/class/pwm/pwmchip1]# echo 60000 > pwm1/period
[  209.133209] ehrpwm 48300200.ehrpwm: Period value conflicts with channel 0
-sh: echo: write error: Invalid argument

However, if I remove one of the submodules, then it seems I can set a period just fine:

[root /sys/class/pwm/pwmchip1]# echo 1 > unexport
[root /sys/class/pwm/pwmchip1]# ls
device     npwm       pwm0       uevent
export     power      subsystem  unexport
[root /sys/class/pwm/pwmchip1]#
[root /sys/class/pwm/pwmchip1]# echo 60000 > pwm0/period
[root /sys/class/pwm/pwmchip1]# echo 1 > export
[root /sys/class/pwm/pwmchip1]# cat pwm1/period
50000
[root /sys/class/pwm/pwmchip1]# cat pwm0/period
60000

What seems odd to me here, is that the periods do not match. I thought they had to be the same. If that is not the case, then why can't I adjust the periods while I have both pwm0 and pwm1 exported?

Once I get in this state of both having different periods, I can continue to modify pwm0 as I wish, but pwm1 can't be modified:

[root /sys/class/pwm/pwmchip1]# echo 70000 > pwm1/period
[  287.953025] ehrpwm 48300200.ehrpwm: Period value conflicts with channel 0
-sh: echo: write error: Invalid argument
[root /sys/class/pwm/pwmchip1]# echo 70000 > pwm0/period
[root /sys/class/pwm/pwmchip1]# cat pwm0/period
70000
[root /sys/class/pwm/pwmchip1]# cat pwm1/period
50000

The only modification that seems to be allowed is to set pwm1 to pwm0's value. However once that occurs neither pwm1 nor pwm0 can be changed anymore.

[root /sys/class/pwm/pwmchip1]# echo 70000 > pwm1/period
[root /sys/class/pwm/pwmchip1]# cat pwm1/period
70000
[root /sys/class/pwm/pwmchip1]#
[root /sys/class/pwm/pwmchip1]# echo 50000 > pwm0/period
[  330.573006] ehrpwm 48300200.ehrpwm: Period value conflicts with channel 1
-sh: echo: write error: Invalid argument

I hope it's not just me, and this seems like a very odd behavior to others. Can someone please help me understand why the PWM period is working like this?

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

Hi,

I will forward this to the SW team.

0 Yordan Kovachev over 8 years ago

TI__Guru**** 161600 points

Hi Mike,

Could you share which SDK is this, so I can test it on my BBB?

Best Regards,
Yordan

0 Mike Worster over 8 years ago in reply to Yordan Kovachev

Expert 1575 points

Yordan Kovachev said:
Hi Mike,

Could you share which SDK is this, so I can test it on my BBB?

This is actually a custom build for our board, but it's based heavily off the 7.00.00.00 SDK for the AM335x EVM

-Mike

0 Yordan Kovachev over 8 years ago in reply to Mike Worster

TI__Guru**** 161600 points

Hi Mike,

I tested this on my BBB, and here is the result:
root@am335x-evm:~# cd /sys/class/pwm/
root@am335x-evm:/sys/class/pwm# ls
pwmchip0 pwmchip2
root@am335x-evm:/sys/class/pwm# cd pwmchip0/
root@am335x-evm:/sys/class/pwm/pwmchip0# ls
device export npwm power subsystem uevent unexport
root@am335x-evm:/sys/class/pwm/pwmchip0#
root@am335x-evm:/sys/class/pwm/pwmchip0#
root@am335x-evm:/sys/class/pwm/pwmchip0#
root@am335x-evm:/sys/class/pwm/pwmchip0#
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm0/enable
cat: can't open 'pwm0/enable': No such file or directory
root@am335x-evm:/sys/class/pwm/pwmchip0# ls
device export npwm power subsystem uevent unexport
root@am335x-evm:/sys/class/pwm/pwmchip0# echo 0 > export
root@am335x-evm:/sys/class/pwm/pwmchip0# echo 1 > export
root@am335x-evm:/sys/class/pwm/pwmchip0# ls
device npwm pwm0 subsystem unexport
export power pwm1 uevent
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm0/enable
0
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm1/enable
0
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm0/duty_cycle
0
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm1/duty_cycle
0
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm0/period
0
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm1/period
0
root@am335x-evm:/sys/class/pwm/pwmchip0# echo 60000 > pwm0/period
root@am335x-evm:/sys/class/pwm/pwmchip0# echo 60000 > pwm1/period
root@am335x-evm:/sys/class/pwm/pwmchip0#

As you can see I don't get the
"[ 202.183000] ehrpwm 48300200.ehrpwm: Period value conflicts with channel 1
-sh: echo: write error: Invalid argument"
error message, and I am able to set 60000 in pwm0/period & pwm1/period without any problems. Moreover, after executing the above commands, the period of pwm0 & pwm1 is the same:
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm0/period
60000
root@am335x-evm:/sys/class/pwm/pwmchip0# cat pwm1/period
60000
root@am335x-evm:/sys/class/pwm/pwmchip0#

My environment is: Beaglebone Black, running SDK7.0: Linux am335x-evm 3.12.10-ti2013.12.01 #1 Tue Sep 8 15:08:17 EEST 2015 armv7l GNU/Linux

What I did was add the following lines in am335x-bone-common.dtsi:
ocp {
epwmss0: epwmss@48300000 {
status = "okay";
ehrpwm0: ehrpwm@48300200 {
pinctrl-names = "default";
pinctrl-0 = <&ehrpwm0_pins>;
status = "okay";
};
};

epwmss1: epwmss@48302000 {
status = "okay";
ehrpwm1: ehrpwm@48302200 {
pinctrl-names = "default";
pinctrl-0 = <&ehrpwm1_pins>;
status = "okay";
};
};

And the following pinmux settings:
ehrpwm0_pins: ehrpwm0_pins {
pinctrl-single,pins = <
0x150 (PIN_OUTPUT_PULLUP | MUX_MODE3)
0x154 (PIN_OUTPUT_PULLUP | MUX_MODE3)
>;
};

ehrpwm1_pins: ehrpwm1_pins {
pinctrl-single,pins = <
0x48 (PIN_OUTPUT_PULLUP | MUX_MODE6)
0x4C (PIN_OUTPUT_PULLUP | MUX_MODE6)
>;
};

Best Regards,
Yordan

0 Brad Griffis over 8 years ago in reply to Yordan Kovachev

TI__Guru*** 125430 points

Mike/Yanko,

This behavior appears to be defined in ./drivers/pwm/pwm-tiehrpwm.c:

        /*
         * Period values should be same for multiple PWM channels as IP uses
         * same period register for multiple channels.
         */
        for (i = 0; i < NUM_PWM_CHANNEL; i++) {
                if (pc->period_cycles[i] &&
                                (pc->period_cycles[i] != period_cycles)) {
                        /*
                         * Allow channel to reconfigure period if no other
                         * channels being configured.
                         */
                        if (i == pwm->hwpwm)
                                continue;

                        dev_err(chip->dev, "Period value conflicts with channel %d\n",
                                        i);
                        return -EINVAL;
                }
        }

The first part of the "if" statement would skip the check in the case that pc->period_cycles[i] is equal to zero. That was the case in Yanko's experiment, but not in Mike's experiment. I see the period gets set back to zero when you free a PWM. So I think if you wanted to make a change to the period you would need to first free the PWM and then configure it.

Brad

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ehrpwm period fails to be changed