Maximum value of PWM period

[NPal.2]

Hi all,

I have configured TIM1_CH3N as a pwm channel.

I am trying to do some PWM functionality here.

I am following current tutorial here. When i tried to provide a period of 10 sec it fails to take up the value.

I get following error :

root@stm32mp157a-visionsom-rgb-emmc-mx:/usr/local/firmware_demos# echo 10000000000 > /sys/class/pwm/pwmchip4/pwm2/duty_cycle pwm2
sh: write error: Invalid argument

100000000

Is there some limit to what value we can provide here?

[Paul1]

Haven't looked in detail at STM32 you are using, but possibly PWM limited to counter (16bit=65535), with prescaler (16bit=65535).

Increase the prescaler (16bit) for slower counting, or change the PWM clock source.

i.e. 100000000 = 10000*10000 = Prescale 10000 * Period 10000

i.e. 100000000 = 50000*2000 = Prescale 2000 * Period 50000

etc.

i.e. .

[S.Ma]

Seems to be a good cubemx opportunity to improve....

[NPal.2]

Hi @Community member​ : Thanks for response. It seems that on Linux front one does not have much control over these. I believe this can be controlled finely on the bare metal front. I am looking for a solution on the Linux front.

[PatrickF · Accepted solution]

Hi,

this is a Linux framework limitation which is using a 32-bits parameter with fixed 1us resolution. So maximum period and duty_cycle are 2^32, i.e. about 4.3 seconds.

I'm not expert, but there is probably other way under Linux (e.g a task started every 1 second which will then manage a GPIO)

Another solution (e.g. if you want TIMx specific features like multichannel, inverted output, etc...) is to handle the TIM with Cortex-M4, then you have full management of TIM count-clock/prescaler/counter/etc...

Regards.

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[NPal.2]

Hi @PatrickF​ Thanks for the clarity. I will use these inputs to solve things at my end. This really helps.

[NPal.2]

Hi @PatrickF​ : Thanks for the answer. Coming back to it , is there lower limit too? I can't seem to set the PWM period for 10ms. It shows up response as Device or resource busy and further going down to 1ms , it straight away says invalid argument.