How to use LPTIM_TimeOut for a simple one-shot delay ?

[Strooom]

I'm trying to realize some simple timings/delays in my application using the LPTIM, and although most of it is working, I don't understand it 100%.

So the LPTIM is set up to run on the LSE clock (32768 Hz) (with a prescaler of 16, so the LPTIM is running at 2048 Hz)

To start a delay there is this HAL function :

HAL_LPTIM_TimeOut_Start_IT(&lptim1, uint32_t Period, uint32_t Timeout)

but why are there 2 parameters ?

If I set Timeout to (eg). 2048, I get the LPTIM interrupt one second later.

But what is Period doing ? What value should it be set in this simple case ?

If I set Period to (eg) 2048 as well, I observed that the first time, I get 2 interrupts, io 1...

Also I found that the timer after expiring, is restarted automatically, so I have to stop it. Would it be possible to start it as a one-shot timer, so it expires automatically ?

It all seemed like a simple application of LPTIM, but I could not find how to do it in the HAL docs not in the forums..

Thanks.

[Strooom]

I think I found a solution in the following way :

Using HAL_LPTIM_SetOnce_Start_IT() to start the timer. It still has two parameters, but I set the 'Period' to 0xFFFF and the 'Pulse' to the timeout time wanted.

Then this generates 2 interrupts : compareMatch and reload, but by adding only HAL_LPTIM_CompareMatchCallback() to handle the timer expire event, it works. The other interrupt (reload) is also firing but it calls an empty HAL_LPTIM_AutoReloadMatchCallback().

I think it could be disabled with some lower level calls, but the available HAL function enables both.

[Amel NASRI]

Hi @Strooom​ ,

To understand more how the LPTIM Timout works, I invite you to look to:

• one of the LPTIM_Timeout examples in STM32CubeL4 package like STM32CubeL4/Projects/NUCLEO-L432KC/Examples/LPTIM/LPTIM_Timeout
• "Timeout wakeup mode" paragraph in AN4865 Low-power timer (LPTIM) applicative use cases on STM32 MCUs and MPUs.

-Amel

[Strooom]

Hi Amel, thanks for your help. Actually I did consult those sources, but I did not find the answer there. Those examples are all focused on using the LPTIM to generate or handle hardware signals. My need was a pure software timer, so I can put the MCU into sleep for some time, and have it wake up after that. It's basically like a HAL_Delay() but then in (ultra) low power.