NRF91 power save mode with CONFIG_SERIAL=y

[MosheSmartAmr]

Hi,

as I understand (and tried), in order to get low power consumption on the NRF91, I need to to get CONFIG_SERIAL=n.

However , I need the uart to be enabled (for short periods of time every few hours).

Is it possible to Change this flag at runtime ?

Thanks,

Moshe

[Yusuke]

I don't know how to solve the issue, but this might help you.

https://github.com/zephyrproject-rtos/zephyr/pull/7034

[Bjørn Kvaale]

You cannot change flags in runtime, but you can turn off the uart RX if needed. See this code for more info.

[Yusuke]

Hi, Bjorn. Thank you so much! This code works out.

void disable_uart(){
        NRF_UARTE0->TASKS_STOPTX = 1;
        NRF_UARTE0->TASKS_STOPRX = 1;

        NRF_UARTE3->TASKS_STOPTX = 1;
        NRF_UARTE3->TASKS_STOPRX = 1;
}

void enable_uart(){
        NRF_UARTE0->TASKS_STARTRX = 1;

        NRF_UARTE3->TASKS_STARTRX = 1;
}

A current around 25uA is consumed on DK v0.8.5 while the UART RX is off. Is this reasonable value? I read datasheet and it doesn't describe current consumption of UART. Let me know the value, if you have measured.

[Bjørn Kvaale]

That seems roughly correct, depending on what you are doing. Maybe this blog post could also help a bit.

[jbrzozoski]

Looking around in the guts of Zephyr and NRFX, the UARTE drivers already have some level of support for disabling them in run-time.  It looks like most of that functionality is tied into the API enabled via CONFIG_SYS_POWER_MANAGEMENT, but that is currently not supported on the nRF9160.  Is that support on the roadmap anywhere?