Bluefruit.begin() causes high power consumption

[jpconstantineau]

Describe the bug
master HEAD-unreleased 0.22.0 has issues with high power consumption when using Bluefruit BLE functions.

Set up (mandatory)

• PC & IDE : Arduino 1.8.13 on Windows 10
• BSP : 0.21.0 vs master-HEAD (0.22.0 WIP)
• Board : nRF52840 module with no power circuitry (connected directly to Nordic Power Profiler)
• Sketch: hid_keyboard with delay(20); added to top of loop() to ensure that CPU has a chance to sleep and lower power consumption

To Reproduce
1 - load hid_keyboard example
2 - add delay(20); to loop(); and comment out while !serial line in setup();
3 - compile/flash with 0.21.0
4 - connect power profiler and get 1.477mA average current when advertising in fast mode and 257uA average current once it settles
5 - Install master-HEAD version of BSP as per readme.md instructions
6 - compile/flash with master-HEAD
7 - connect power profiler and get 7.451mA average current when advertising in fast mode and 6.408mA average current once it settles

Screenshots
See screenshots of power consumption indicated above. (links to come...)

Serial Log
None needed

Notes
A brief analysis by commenting things out indicates that Bluefruit.begin(); is what triggers the issue.
This means that some of the changes implemented to handle background tasks do not put the CPU in sleep mode.

[jpconstantineau]

Screenshots of Nordic Power Profiler:
0.21.0

master-HEAD (0.22.0 WIP)

[hathach]

it is probably due to the PR #466 which make use of the CC310 cryptocell subsystem for performing LESC pairing. Maybe we should enable when needed only. For now I don't have the bandwidth to look at this, however if you could verify the current is indeed started increased after #466 it will help me to later on when looking at the issue.

[jpconstantineau]

I went through the commits from 0.21.0 and on and did find the one that caused the high power consumption:

ce81b83 1.4mA 245uA
1eae55e 1.37mA 240uA
7e64023 1.37mA 241uA
dc2802a 7.44mA 6.4mA

It is indeed PR #466 that caused the issue.

[hathach]

thanks @jpconstantineau for testing and confirmation, I am currently on other work, will take a look at this later on.

[jpconstantineau]

Tested HEAD by reverting #466 away from all the commits on my own fork and can confirm that power consumption is still at 1.4mA and 241uA without the content of that PR#466 merge. Doing a git revert might be messier than fixing it but could be an option to bring everything else that was added after that PR.

[hathach]

Revert won't be an option. We will fix it when we have time to work on this later on.

[mark9064]

Do you think you will have time to revisit this issue soon? The increased power consumption is a deal breaker for a project of mine ☹️

[selman-nus]

BLE power consumption is also highly important for me. Waiting for any updates.

@jpconstantineau Is there a way to use power profiler kit on other boards? (Other than nrf52 devkit)

[jpconstantineau]

I have the first version of the power profiler. Although you need to have it on top of a dev kit, you can measure an external device (i.e. a custom board) by using the "External DUT" header to power your custom board.

The newer version of the power profiler does not need a dev kit.