is there a chance a hardware timer ISR not be triggered in a busy system?

Weizzh
Posts: 9
Joined: Mon Nov 22, 2021 9:32 am

is there a chance a hardware timer ISR not be triggered in a busy system?

Postby Weizzh » Fri Jan 21, 2022 6:57 am

HI there.
I set a hardware timer work at 4000 hz. When the isr is triggered, I will read some gpio status to a buffer. When the buffer is full, send a messsge to a queue and then other tasks can do some data processing for example publishing these data through mqtt.
Well, the data I get is bad. I found some data lost somewhere. The isr seemes to be triggered less than 4000 times.
Is there any chance the isr not triggered because of other tasks?
I tried to set the isr to ESP_INTR_FLAG_HIGH, and this time the isr isn't triggered even once. Am I missing something?

hustenhabas
Posts: 18
Joined: Tue Sep 14, 2021 2:18 pm

Re: is there a chance a hardware timer ISR not be triggered in a busy system?

Postby hustenhabas » Fri Jan 21, 2022 8:41 pm

Hello. Ive had this problem recently and it was because I was sending the Timer ISR event to a xQueue. What I did to fix it was handling the event inside the ISR and not sending it to xQueueRecive somewhere. My timer was 104 microseconds and it worked (My project was a bitbanged uart so i needed a very precise timer interrupt).

wrong example:

Code: Select all

void timer_isr() {
	xQeueSend()
}
void task_loop() {
	xQueueRecive()
	DoStuff()
}
right example:

Code: Select all

void timer_isr() {
	DoStuff();
}
if you use a task to recive the queue events it might get suspended to run other tasks. Increasing its priority was not enogth for me

Weizzh
Posts: 9
Joined: Mon Nov 22, 2021 9:32 am

Re: is there a chance a hardware timer ISR not be triggered in a busy system?

Postby Weizzh » Sun Jan 23, 2022 6:11 am

Thanks. It worked.
I've changed the code from

Code: Select all

void timer_isr() {
	xQeueSend()
}
void task_loop() {
	xQueueRecive()
	DoStuff()
}
to

Code: Select all

void timer_isr()
{
	set_a_flag
}

void observer_task
{
	loop()
	{
		check the flag
		xQueueSend
		clear the flag
	}
}
void task_loop()
 {
	xQueueRecive()
	DoStuff()
}
In fact, it is not the first time xXXXfromISR() functions of freeRTOS don't work as expected.
Hope these fetures can be tested thoroughly so developers can acknowledge more details.

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