PROCESSOR-SDK-AM62X: Why can two PWMs only use the same period value?

Hello Daniel,

Thank you for the query.

Daniel Cheng1 said:

Pin define

B17	EHRPWM2_A	EHRPWM	PWM,Buzzer Control
A17	EHRPWM2_B	EHRPWM	PWM,LCM Backlight Control

These seem to be complementary PWMs.

Is the query related to Hardware or Software.

Regards,

Sreenivasa 

Hi Sreenivasa 

The customer wants to know how to control the buzzer and backlight brightness to different frequencies? Can the same set of pwm be used or do two sets of pwm be used to control different frequencies?

Thanks

Daniel

Hello Daniel,

Thank you.

Is customer referencing to an SK or is this a customer design?

I would expect separate PWMs to be used for brightness and Buzzer control.

Regards,

Sreenivasa

Hi Sreenivasa

The customer's custom board design is based on SK-AM62B-P1.

Customers are currently using PWM2_A and PWM2_B.

So does the custom hardware design have to be designed as PWM2_A and PWM1_A or PWM2_A&PWM0_A?

Why does the design of PWM2_A and PWM2_B not work properly?

Thanks

Daniel

Hello Daniel,

Daniel Cheng1 said:

Why does the design of PWM2_A and PWM2_B not work properly?

You need to share the schematics for me to review or check internally.

Regards,

Sreenivasa

Hi 

Please check this schematics, thanks

Hello Scott, 

Thank you.

Have you reviewed the TRM. EPWN section to configure the PWM ouput to work independently.

Please share the configuration used in the software.

Regards,

Sreenivasa 

Hello  Sreenivasa

please see the picture log that Daniel provided.

we try to set different period and failed

thanks

Hello Scott, 

Thank you.

I will have to assign the query to a software expert.

Let me check and update.

Regards,

Sreenivasa

Hello Scott, 

I am assigning to the expert.

Can you confirm if you are using Linix.

Regards,

Sreenivasa

I follow TI SDK  https://software-dl.ti.com/processor-sdk-linux/esd/AM62X/10_01_10_04_Buildroot/exports/docs/buildroot/Overview.html

Buildroot is an open-source, simple, and efficient tool for building complete Linux systems for embedded devices

From dmesg log

Linux version 6.6.58 (scott@BuildServer) (aarch64-buildroot-linux-gnu-gcc.br_real (Buildroot 2024.05.3) 13.3.0, GNU ld (GNU Binutils) 2.41) #33 SMP PREEMPT Wed Jul  2 16:23:56 CST 2025

Hi Sreenivasa

Please help to assign the ticket. thanks

Hello Scott,

Thank you for following, the thread has been assigned for the expert to support.

Regards,

Sreenivasa

Hello all,

Help me understand exactly what you are doing in your test setup here.

If you are controlling the EPWM instance from Linux, please note that the PWM period and duty cycle for both output A and output B must be configured BEFORE enabling either of the PWM channels. The Linux driver does not support modifying the PWM period while either PWM output is active.

So if you enabled output A, and THEN tried to configure output B, the Linux driver would complain.

Regards,

Nick

More information about using the TI PWM driver is in the Linux SDK docs here: https://software-dl.ti.com/processor-sdk-linux/esd/AM62X/11_00_09_04/exports/docs/linux/Foundational_Components/Kernel/Kernel_Drivers/PWM.html 

Hi Saulnier

thanks for the explain

My understanding is if we choose either one of them (in our case is EHRPWM2_B backlight will enabled during linux boot) and the period is fixed.

We can't change the other one EHRPWM2_A by sysfs due to the period is fixed by backlight.

Is it correct? 

Hello Scott,

That is my understanding.

If you know what the period of PWM2_A needs to be during boot time, perhaps you could configure both periods before enabling the backlight? Or disable the backlight during runtime for just long enough to set the period for both PWM outputs, before re-enabling the backlight?

I have not looked into the exact implementation of "backlight uses one PWM output of a PWM module, a different driver uses the other PWM output". It might require some software hacking if you need 2 different drivers interacting with the same PWM module, rather than a userspace application configuring the outputs during runtime.

Regards,

Nick