Associate III

Question

Can FreeRTOS software timer generate PWM?

Forum|Forum|1 month ago
April 29, 2026
6 replies
679 views

Hello, i am using F446 and i am contemplating using FreeRTOS CMSIS V2 software timer to generate PWM to control motors via motor drivers (IC chipset). Is this possible? Or must I use the hardware timer, TIM1~7 ?

Andrew Neil

Super User

@HMSEdinburge wrote:
must I use the hardware timer, TIM1~7 ?

Why would you not want to use them? This is exactly what they're for !

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.

H

HMSEdinburgeAuthor

Associate III

Ok, but can this FreeRTOS software timer produce PWM like the hardware timer? Can they driver a motor?

Please share source code of software timer generating PWM, thx.

Andrew Neil

Super User

Of course it can be done - just like bit-banging any other interface.

But you will never reach anywhere near the performance of a dedicated hardware timer.

Your code will need to manually make every single output transition and timer adjustment - and fit this around whatever else your code is doing.

But it's just software; you can easily try it out - but pay particular attention to the CPU usage ...

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.

LCE

Principal II

Then check if the hardware timers are really needed for the stuff they are doing now.

If your PWM is really slow (like <= 1 kHz carrier or so), then maybe software can handle this well enough.

Otherwise - not at least a 10 kHz interrupt available or so?

But all this doesn't really make sense in a device that has hardware / timers built for that purpose.

H

HMSEdinburgeAuthor

Associate III

all my hardware timer TIM1~7 all used, therefore only left software timer, but can software timer able to drive an external motor?

Andrew Neil

Super User

@HMSEdinburge wrote:
can software timer able to drive an external motor?

A timer - whether software or hardware - just toggles an output pin.

It makes no difference to the timer (whether SW or HW) what is externally connected to that pin.

As @LCE said, the limitation on using SW timers is going to be the maximum speed achievable.

Also the CPU load.

But, again, you can easily just try it out: write some code to toggle a pin, watch it on your scope, check CPU utilisation...

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.

G

Gyessine

Technical Moderator

Hello @HMSEdinburge
Well, it's doable but as @Andrew Neil and @LCE but do not expect high precision. Software timers can be used for motor control in low-precision or low-frequency applications. However, they are not a substitute for hardware timers when precise timing is required.

If the software timer you want to create have the same frequency and period as one of the hardware timers, you can create a variable that captures the hardware timer CNT register. Compare this variable with specified value (like a custom ARR) as a condition to perform the required task when the CNT register reaches the desired value for the software timer. This approach may improve precision slightly.

BR
Gyessine

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mƎALLEm

Technical Moderator

As said by @Andrew Neil ,

There are 14 timers in STM32F446:

You are using half of timers resources in your case only 1 to 7 in your case.. So why bothering yourself with the software timer usage?

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H

HMSEdinburgeAuthor

Associate III

Hi there, i got total 63 motors to control. F446 has 14 timer, TIM6 and TIM7 is a general timer, does not have CCR and AAR registers, so cant use for PWM.

Anyone has the source code for software timer using FreeRTOS CMSIS V

mƎALLEm

Technical Moderator

@HMSEdinburge wrote:

Hi there, i got total 63 motors to control.

Anyone has the source code for software timer using FreeRTOS CMSIS V

63 motors to be controlled with STM32F446 with FreeRTOS software timer to generate PWM?

I don't think this is feasible. Think about the CPU load and the accuracy of the PWM duty cycle!

This is something that needs to be done with hardware ..

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AScha.3

Super User

Hi,

to get good info, you should also give some good info:

- how many motors need control at same time ?

- which kind of motor and driver ? (DC, stepper, 3-phase ...etc)

- needed speed of pwm or control signal ?

- and resolution of pwm needed (how many steps from 0...100% ) ?

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H

HMSEdinburgeAuthor

Associate III

These are the motors i m using, BLDC, stepper, servo actuators, stepper motor need 1/32 steps, BLDC needs PWM, and their various motor drivers, gate drivers etc. Total 63 motors.