Zephyr RTC Alarm versus k_timer_start

[Jamal_nRF]

Dear Customer Support,

Wanted to open a case to follow up on this old one Case ID: 335484  

 nRF52840 with Zephyr RTOS: How to use RTC with struct rtc_time? 

I initially looked at the counter alarm under

https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/drivers/counter/alarm/src

using rtc0 and counter_set_channel_alarm

Test environment nRF52840, but this seems to be pretty generic to any other nRF platform

I have few high level questions:

1-what would be the pros and cons of using the Zephyr counter alarm feature versus using the plain Zephyr k_timer_start with a registered callback?

2-with the counter alarm feature, there is an upper limitation on the alarm duration around 8 second, as obtained by

counter_get_top_value or counter_get_max_top_value

how to increase that maximum tick value to configure a higher duration value?

3-if we force the device into a power off state using sys_poweroff(), is there a possibility to wake up the device through an RTC callback

There is an available sample that shows how to wake up using a button press, so the idea is to replace the button by a RTC wake up

Thank you

Jamal

PS

I will have more follow up questions later...

[Kazi Afroza Sultana]

Hello,

Here are the answers of your questions from the first thread:

1. the counter/alarm functionality does not handle timer rollover (overflow), meaning that whenever the underlying peripheral, RTC or TIMER, counts from 0 -> MAX, this will be the maximum duration of your alarm. k_timer handles overflow/rollover.
2. Library does not handle rollover. See the implementation for more specific details: https://github.com/nrfconnect/sdk-zephyr/blob/v3.7.99-ncs1-branch/drivers/counter/counter_nrfx_rtc.c
3. Only nRF54L can have the GRTC running in systemoff and wake up on GRTC. Other nRF devices has only combinatory logic (level triggered, for instance button press) that can be enabled in system off.

[Jamal_nRF]

Re: Only nRF54L can have the GRTC running in systemoff and wake up on GRTC.

This is important information!

Reviewing the product specification document nRF52840_PS_v1.11.pdf / Sectin 5.2.1.1 Sleep

There is a mention of "System ON, no RAM retention, wake on RTC (running from LFRC clock)"

But no mention of "wake on RTC" when in System OFF state

However, there is a mention of "System OFF, no RAM retention, wake on LPCOMP"

What is LPCOMP?

I understand that a button press configuration would allow a wake up from System OFF state. There is a sample demonstrating that.

Jamal