How can I set PWM to input capture mode in Linux for EV1 board?

[cfilipescu]

I am trying to configure the TIM2_CH4 to capture mode on EV1 board so I can sense a fan speed from a PWM fan but I keep getting

cat: read error: Connection timed out

I have configured the timer as follows:

&timers2{
 pinctrl-names = "default", "sleep";
 pinctrl-0 = <&tim2_pins_mx>;
 pinctrl-1 = <&tim2_sleep_pins_mx>;
 status = "okay";
 
 /* USER CODE BEGIN timers2 */
 dma-names = "ch3";
 pwm {
 /* enable PWM on TIM2 */
 status = "okay";
 };
 /* USER CODE END timers2 */
};

 tim2_pins_mx: tim2_mx-0 {
 pins {
 pinmux = <STM32_PINMUX('A', 3, AF1)>; /* TIM2_CH4 */
 bias-disable;
 drive-push-pull;
 slew-rate = <0>;
 };
 };
 
 tim2_sleep_pins_mx: tim2_sleep_mx-0 {
 pins {
 pinmux = <STM32_PINMUX('A', 3, ANALOG)>; /* TIM2_CH4 */
 };
 };

I am using TIM12_CH1 to generate a pulse and I have shorted the two pins on the board.

What am I doing wrong? Is there a better way to detect the sense on a PWM fan?

[PatrickF]

Hi,

this wiki page could help you:

https://wiki.st.com/stm32mpu/wiki/PWM_overview#How_to_use_PWM_capture_with_sysfs_interface

Regards.

[cfilipescu]

Hi @PatrickF​ ,

That is the link I used but it doesn't seem to work, is there any other helpful material or example?

[cfilipescu]

I needed to remove the following line:

dma-names = "ch3";

The instructions are misleading.

[PatrickF]

Hi @cfilipescu​ ,

I agree Wiki is misleading or most probably outdated.

Looking at DTS, for timer2 CH4, it should have been

 dma-names = "ch4";

to use DMAMUX channel TIM2_CH4

We will ask for a wiki update/clarification.

Regards.

[PatrickF]

I got confirmation that wiki is OK.

In fact, PWM capture will use two timer channels (e.g. timer capture 1+2 for CH1 or CH2 pins and timer capture 3+4 for CH3 or CH4 pins) but one single DMA request to get period and duty-cycle ("ch1" DMA for timer capture 1+2 and "ch3" DMA for timer capture 3+4),

In your DT, you probably missed to enable the relevant DMAMUX channel, e.g.

 /* Enable DMA "ch3" for PWM input on TIM2_CH4 */
	dmas = <&dmamux1 20 0x400 0x5>;
 dma-names = "ch3";

but I have not tested it.

Regards.

Regards,

Patrick