Unable to obtain low power use when idle

RE: Unable to obtain low power use when idle

helsing — Thu, 21 Sep 2023 13:21:56 GMT

Great to hear that you were able to lower the current.

[quote user="hahe"]The modem will draw a large current (a few mA) if it has not been initialized. After initialized the current will drop to a few uA. (This is listed as an errata/known issue, I will post the link later.)[/quote][quote user="rogierl"]Btw, initializing the modem in my code lowered the current draw by ~1mA and you mentioned that not initializing the modem causes a current draw of "a few" mA's. So this being lower than expected was actually a pointer in this direction. (in hindsight things like this are always much easier to see... ;))[/quote]

Sorry, I forgot to post the link to the Known Issue in Zephyr, "NCSDK-10106: Elevated current consumption when using applications without Modem library on nRF9160". This should lower the sleep current from 3mA down to a few uA. Check PR #5648 to see how the modem library is enabled when building samples for nRF960.

RE: Unable to obtain low power use when idle

rogierl — Wed, 20 Sep 2023 07:40:56 GMT

Ok.. I knew it had to be something trivial...

I think I have found the leak; somewhere hidden in my code I had the line:

core::ptr::write_volatile(0x4000_5C04 as *mut u32, 0x02);

Which is a mitigation for anomaly [17] Debug and Trace: LTE modem stops when debugging through SWD interface This erratum has been long-fixed in the production hardware revisions, so is never needed anymore. 🤦

Anyway, the mystery seems solved, so very happy with that. :) Now we can properly power-optimize the design further.

Btw, initializing the modem in my code lowered the current draw by ~1mA and you mentioned that not initializing the modem causes a current draw of "a few" mA's. So this being lower than expected was actually a pointer in this direction. (in hindsight things like this are always much easier to see... ;))

Anyway, I will close the ticket. Thanks for your time and help!

RE: Unable to obtain low power use when idle

rogierl — Tue, 19 Sep 2023 15:00:06 GMT

Hi Helsing,

Thanks for getting back! Yes indeed, I got in contact with the very helpful local Application Engineer. I had a nice conversation with him, but unfortunately this didn't materialize into concrete pointers to the issue at hand. (The FAE will be forwarding me some additional information/pointers regarding the issue).

In the mean time I did some more "fiddling" and got the power down to 1.2mA, not a huge improvement, but nevertheless an improvement. This was the result of disabling the DC/DC converter on the SoC. (peripherals.REGULATORS_NS.dcdcen.write(|w| w.dcdcen().disabled()))

So, in summary power use comes to this now:

Just call `wfi()`: 2.7mA
Init modem before: 1.7mA
Disable (i.e. don't enable) DC/DC convertor: 1.2mA
SYSTEM_OFF: 2-4µA

Note: the current draw in SYSTEM_OFF mode can be "wandering about" (up to a couple of 100µA). This looks to be caused by dangling GPIO lines, the lowest power in SYSTEM_OFF mode is obtained when all GPIO pins' SENSE setting is disabled.

For reference disabling most peripherals (code below), does not make seem to make any difference to the power use. Therefore I'd reckon that the peripherals weren't enabled in the first place. Something else must be sucking some power (maybe some peripheral in the _S (secure) partition, would that be a possibility? Or maybe some ARM core peripheral (already tried disabling SYSTICK)...?

For reference the (not very exciting, Rust) code for disabling most peripherals:

pub fn disable_periphs(p: &Peripherals) {
    defmt::println!("Disabling periphs!");

    p.UARTE0_NS.enable.write(|w| w.enable().disabled());
    p.UARTE1_NS.enable.write(|w| w.enable().disabled());
    p.UARTE2_NS.enable.write(|w| w.enable().disabled());
    p.UARTE3_NS.enable.write(|w| w.enable().disabled());

    p.TWIM0_NS.enable.write(|w| w.enable().disabled());
    p.TWIM1_NS.enable.write(|w| w.enable().disabled());
    p.TWIM2_NS.enable.write(|w| w.enable().disabled());
    p.TWIM3_NS.enable.write(|w| w.enable().disabled());

    p.TWIS0_NS.enable.write(|w| w.enable().disabled());
    p.TWIS1_NS.enable.write(|w| w.enable().disabled());
    p.TWIS2_NS.enable.write(|w| w.enable().disabled());
    p.TWIS3_NS.enable.write(|w| w.enable().disabled());

    p.SPIM0_NS.enable.write(|w| w.enable().disabled());
    p.SPIM1_NS.enable.write(|w| w.enable().disabled());
    p.SPIM2_NS.enable.write(|w| w.enable().disabled());
    p.SPIM3_NS.enable.write(|w| w.enable().disabled());

    p.SPIS0_NS.enable.write(|w| w.enable().disabled());
    p.SPIS1_NS.enable.write(|w| w.enable().disabled());
    p.SPIS2_NS.enable.write(|w| w.enable().disabled());
    p.SPIS3_NS.enable.write(|w| w.enable().disabled());

    p.PWM0_NS.enable.write(|w| w.enable().disabled());
    p.PWM1_NS.enable.write(|w| w.enable().disabled());
    p.PWM2_NS.enable.write(|w| w.enable().disabled());
    p.PWM3_NS.enable.write(|w| w.enable().disabled());

    p.SAADC_NS.enable.write(|w| w.enable().disabled());

    p.TIMER0_NS.tasks_stop.write(|w| w.tasks_stop().trigger());
    p.TIMER1_NS.tasks_stop.write(|w| w.tasks_stop().trigger());
    p.TIMER2_NS.tasks_stop.write(|w| w.tasks_stop().trigger());

    p.RTC0_NS.tasks_stop.write(|w| w.tasks_stop().trigger());
    p.RTC1_NS.tasks_stop.write(|w| w.tasks_stop().trigger());
}

RE: Unable to obtain low power use when idle

helsing — Fri, 15 Sep 2023 14:53:06 GMT

Hi Rogier, sorry for the delay. I understand that you are in contact with our FAE. Please let us know if you would like to continue parts of the discussion here.

RE: Unable to obtain low power use when idle

rogierl — Mon, 11 Sep 2023 10:43:06 GMT

helsing Any more insights on this?

RE: Unable to obtain low power use when idle

rogierl — Thu, 07 Sep 2023 09:05:04 GMT

Hi Helsing, thanks for your feedback on this!

Ok.. so the modem current drop has been accounted for 🙂 Good to know that the modem does need to be initialized for any application, even when the modem is not used.

Does this also explain the 1.5mA draw after setting "REGULATORS.SYSTEM_OFF" to 1 without initializing the modem (i.e. modem power domain isn't touched by this setting)?

Thing like this (e.g. the need for modem initialization) get lost in the Zephyr examples, as errata like this are handled/fixed "below the hood". The Zephyr example code I used to establish the 4µA baseline only included a single zephyr.h and issued a single printk(), that's it. All device initing is done outside of application's view. In many cases this probably is good thing, but it doesn't help to easily grasp what's really going on...

On your second note about the UART

As far as I know, I'm not using the UART, at least not in my application code. Would it be possible the SPM did enable the UART (or some other peripheral)? And when it does so in Secure environment, I guess I cannot disable it again from a NS application? Given the 1.7mA draw it seems that the HF clock is running, agree?

RE: Unable to obtain low power use when idle

helsing — Wed, 06 Sep 2023 12:51:57 GMT

Here is a quick update with a couple of thoughts that come to mind.

The modem will draw a large current (a few mA) if it has not been initialized. After initialized the current will drop to a few uA. (This is listed as an errata/known issue, I will post the link later.)
Is the UART disabled in the hello_world sample? Disabling the UART will also make the current drop.

RE: Unable to obtain low power use when idle

helsing — Tue, 05 Sep 2023 15:35:32 GMT

Hi Rogier, I just wanted to let you know I have started looking into this.