Sleep tracing

[bulislaw]

Dependencies

• Sleep handbook improvements #423

Description

Add explanations how to use the new sleep tracing mechanism.

Content

After merging #423 and rebase, this will look like:

Sleep tracing

Mbed OS can help you to understand the sleep patterns of your device, specifically who is holding a sleep locks preventing your board to enter the deep sleep. To enable the tracing, all you need to do is to define MBED_SLEEP_TRACING_ENABLED macro. You can do it by modifying your mbed_app.json config file or appending -DMBED_SLEEP_TRACING_ENABLED to mbed compile command.

Mbed OS will print sleep traces on the standard output, which by default is UART. Some of the events that we track:

• Locking deep sleep: LOCK: <file name>, ln: <line in file>, lock count: <number of locks held>
• Unlocking deep sleep: UNLOCK: <file name>, ln: <line in file>, lock count: <number of locks held>
• Entering sleep: Mbed OS will print a list of locks preventing the board from entering a deep sleep:

Sleep locks held:
[id: <file name 1>, count: <number of locks>]
[id: <file name 2>, count: <number of locks>]

Example trace can look like:

LOCK: mbed_rtx_idle.cpp, ln: 129, lock count: 2
Sleep locks held:
[id: mbed_wait_api_, count: 1]
[id: mbed_rtx_idle., count: 1]
UNLOCK: mbed_rtx_idle.cpp, ln: 131, lock count: 1
LOCK: mbed_rtx_idle.cpp, ln: 129, lock count: 2
Sleep locks held:
[id: mbed_wait_api_, count: 1]
[id: mbed_rtx_idle., count: 1]
UNLOCK: mbed_rtx_idle.cpp, ln: 131, lock count: 1

Note: Sleep tracing is a debug feature and should only be enabled during development cycle. Its heavy use of UART can affect the device performance.

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CC: @scartmell-arm

[AnotherButler]

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