EFM32: Sleep function does not cause the MCU to go to a sleep mode

[seppestas]

In mbed-os 5 and later versions of the mbed 2 SDK (aka mbed-dev), the sleep() function does not cause EFM32 MCUs to sleep properly, even when no sleep levels have been blocked.

When testing on the EFM32 Happy Gecko 322 using the EFM32HG_STK3400 target the MCU still consumes 3.49mA at 3v3 when calling sleep in a loop. I was able to reproduce this in:

• mbed-os 5 at f4864dc
• the pre-compiled mbed lib at 093f2bd7b9eb
• mbed-dev revision d5399cc887bb

I tested both on the STK3400 devkit and a custom breakout board for the EFM32HG322 MCU.

Using mbed-dev at revision d6373279a6f1 using a custom build script and the mbed online compiler I did not have this issue yet. I am still trying to build this revision using the mbed tools.

I still plan to test on other EFM32 MCU's, but since a lot of code is shared I'm guessing the results will be similar.

---

Bug

Target
EFM32

Toolchain:
GCC_ARM

Toolchain version:
4.9.3

mbed-cli version:
1.0.0

[chrissnow]

I had a similar problem with the PG, it's to do with sleep being disabled in debug builds.

#ifdef NDEBUG
#if DEVICE_SLEEP
    hal_sleep();
#endif /* DEVICE_SLEEP */
#endif /* NDEBUG */

if you define NDEBUG it should sleep correctly.

[chrissnow]

Also you may need to power cycle the processor to get it out of debug mode after programming or it still wont sleep.

[seppestas]

Thanks @chrissnow, this seemed to be the problem indeed! I did not know about the hal_sleep functionality. IIRC this was not there in mbed 2 yet.

It would be nice to have this sort of stuff documented on e.g the Power-Management cookbook. Notice the example won't work in the Debug build (which seems to be the default).

Edit: I checked: the sleep_api.h file only contained the sleep and deepsleep function in the version of mbed I used before.

[bulislaw]

Actually I think we need to update that, and made the board not go to sleep only in the debug profile, as opposed to the default developand the release. I'll try to cook something up later today. And update the build profile docs.

[seppestas]

@bulislaw great, thanks.

Let me know if I can be of help, I'm currently looking into the power consumption of leuart on the EFM32 Happy Gecko and I'm building up some interesting scope images.

[bulislaw]

#4097 changes to sleep

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-360

[cmonr]

Closing as issue appear to be fixed.