[riot-notifications] [RIOT-OS/RIOT] cpu/stm32l4: add STOP and STANDBY low-power modes (#11173)

Alexandre Abadie notifications at github.com
Wed Mar 13 17:04:55 CET 2019

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### Contribution description

This PR is adding STOP and STANDBY low-power to stm32l4 MCU family. There are 3 levels of STOP modes for L4, this PR uses STOP1 because I found less constraint (more peripherals can be used during this mode). Even if possible, the SRAM2 retention is disabled during standby mode.

On a nucleo-l433rc or nucleo-l476rg, I got the following consumption results:
- stop: ~8.5uA
- standby: ~0.5uA

For standby mode, the wake-up pins are disabled because when enabling them, there's an important consumption increase (around 300uA). On the l4 boards I have, except l496zg, one of the wake-up pin (PA2) in connected to the stdio UART: this crashes the cpus when entering standby mode and this wake-up pin is enabled.

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### Testing procedure

- Build an flash `tests/periph_pm` on a nucleo-l476rg
- Plug a multimeter on the IDD pins in Amper mode measurement
- Switch to STANDBY mode:
> unblock 0
> unblock 1
> unblock_rtc 1 5
You should see a drop of consumption from 3.8mA to 0.5uA. After 5 seconds, the board reboots.
- Switch to STOP mode:
> unblock 1
> unblock_rtc 1 5
You should see a drop of consumption from 3.8mA to 8.5uA

Details steps to test your contribution:
- which test/example to compile for which board and is there a 'test' command
- how to know that it was not working/available in master
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### Issues/PRs references


Examples: Fixes #1234. See also #5678. Depends on PR #9876.

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-- Commit Summary --

  * cpu/stm32_common: implement low-power modes for L4
  * cpu/stm32l4: use pm_layered module

-- File Changes --

    M cpu/stm32_common/include/periph_cpu_common.h (3)
    M cpu/stm32_common/periph/pm.c (24)
    M cpu/stm32l4/Makefile.include (2)

-- Patch Links --


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