KL03 LLWU wakeup — no module sources?

[jrychter]

I recently started using the KL03 and really like it. It's a good combination of features for an excellent price, and comes in very useful QFN16 and QFN24 packages. But, just as I wanted to use it for a sensor node project, I noticed this on page 235 of the SFRM:

19.1 Chip-specific LLWU information

This device has no LLWU module wakeup source and uses the external pin inputs only of LLWU_P4 and LLWU_P7 as wakeup source to the LLWU module.

This has far-reaching consequences. In particular, it means that the only way to wake up from VLLSx modes is by external pin input. If you're building a sensor node, you want the node to wake up periodically to do something (e.g. check temperature), send the result, and then go to sleep. Most sensor nodes will spend most of their lifetime sleeping. And yet in the KL03, which is described in the datasheet as:

Ideal solution for Internet of Things edge nodes design with ultra small form factor and ultra low power consumption.

… there seems to be no way to implement this behavior using VLLS sleep. If we enter VLLS, we can only wake up through external input, which might not be available (think a temperature monitoring node).

So, the lowest consumption sleep mode that can be used without requiring LLWU module input is VLPS. At a nominal 2.2uA instead of VLLS0 with 0.265uA we're talking 7.3x larger power consumption. I can't help but wonder — am I missing another method to implement sensor nodes that need periodic wakeup? Or is that an oversight when specifying the chip?

[kerryzhou]

Hi Jan Rychter,

      Mark is correct, although the LLWU module don't contain the internal wakeup source, but you still can use the internal peripheral interrupt to wake up the VLLSx power mode.

      Eg, LPTMR, RTC using LPO clock source in VLLS1/3 module, because 1Khz LPO is OFF in VLLS0, then you can't use the LPTMR and RTC to wakeup the VLLS0.

      From the above, I suggest you use the VLL1/3 power mode, then use RTC or LPTMR with 1Khz LPO clock source to wakeup the low leakage mode.

      If you use the KSDK1.3.0, you will find the sample code for FRDM-KL03 is using RTC to wakeup VLL1/3, after you install the KSDK1.3.0, you can find the sample code in the folder:

C:\Freescale\KSDK_1.3.0\examples\frdmkl03z\demo_apps\power_manager_hal_demo

Wish it helps you!

If you still have question, please let me know!

Have a great day,
Jingjing

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[jrychter]

Oh, so *that's* what I was missing! Thanks for explaining! That's very good news.

I'm still slightly puzzled though, as I don't understand the mechanism of the wakeup. It isn't strictly necessary, but I would like to understand it better.

LPTMR peripheral documentation says:

The LPTMR interrupt is generated asynchronously to the system clock and can be used to generate a wakeup from any low-power mode, including the low-leakage modes, provided the LPTMR is enabled as a wakeup source.

It doesn't mention LLWU, but normally "wakeup source" means "LLWU wakeup source", how can I enable another wakeup source if not in the LLWU?

Also, the "Power Management" section says (for VLLS1):

NVIC is disabled; LLWU is used to wake up

I'm assuming it's the AWIC which does the processing and performs wakeup, then?

I'm guessing the relevant section is 7.4 "Entering and exiting power modes" (page 82), which says:

For VLLS modes, the wake-up sources are limited to LLWU generated wake- ups,LPTMR, CMP, SRTC,NMI_b pin, or RESET_b pin assertions.

But that doesn't list RTC as a wakeup source.

(and yes, I meant VLLS1 not VLLS0, I was hoping to use VLLS1 sleep and LPTMR or RTC wakeup for the sensor nodes)

In any case, many thanks for your explanations, Mark and Jingjing.

[mjbcswitzerland]

Hi

SRTC

I think this is a typo in the user manual - therefore the RTC is mentioned.

Regards

Mark

[mjbcswitzerland · Accepted solution]

Hi

The LPTMR and RTC (and CMP) can be used to exit the low leakage modes in the KL03 (all via a reset).

I think the line that followed the one that you referenced hints to this - they just don't pass through the LLWU module as is the more usual case.

See the peripheral chapters of these sources for additional details.

Regards

Mark

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