Add missing free function to lp and us ticker HAL APIs

[ghost]

Description

The current HAL specification for tickers does not provide a method to disable them, which is an issue for low power mode. This PR adds free functions similar to that defined in the RTC HAL API to both the us ticker and lp ticker APIs.

Status

IN DEVELOPMENT

Migrations

NO

Todos

• Add function declaration to HAL header files
• Add support for boards currently using the API.

[0xc0170]

Does this need to go to feature branch and have all targets implemented?

If this API is defined, shouldn't be used somewhere? Us ticker is always running at the moment (overflow to count 64bit timestamp) - how does this work with this extension?

Shall lp ticker be disabled?

[ghost]

It should go to the ticker feature branch until it's implemented on the necessary boards.

The tickers should stop counting after being freed if they were initialised, I'm not certain of the behaviour yet if multiple tickers rtc/us/lp are running and share the same counter.

[bulislaw]

I think you need to rebase your code on top of the rtos ticker branch and update the undefined behaviour section on the beginning of the header.

[0xc0170]

@scartmell-arm Please advice what is the destination branch, still points to master - seems incorrect.

[0xc0170]

@scartmell-arm Can you rebase please after changing the destination branch?

[pan-]

Could you explain how and when the ticker free function is supposed to be used ?

A module calling us_ticker_free after it's use of the us_ticker may interfere with other parts of the application that are currently using the peripheral.

[bulislaw]

We are adding way of powering things off to all HAL APIs, the driver will need to figure out how to use it. I'm not sure it will be possible to do for all the drivers for Mbed OS 5, due to backward compatibility requirements. As for us ticker I don't want it being used by Mbed OS if we can avoid it, therefore it will be up to the user to manage it's lifetime.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 958
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/5856/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 643
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/5856/

[mbed-ci]

Test : SUCCESS

Build number : 785
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/5856/785

[0xc0170]

/morph uvisor-test