Fix for PWM resume issue, SWINTEGRATION-57

[billwatersiii]

Summary of changes

This is a workaround for the problem described here - #15135 (comment)

The PwmOut::resume() function in mbed-os/drivers/source/PwmOut.cpp sets the "percentage of the period" (the duty cycle) before it sets the period.

void PwmOut::resume()
{
    core_util_critical_section_enter();
    if (!_initialized) {
        PwmOut::init();
        PwmOut::write(_duty_cycle);
        PwmOut::period_us(_period_us);
    }
    core_util_critical_section_exit();
}

We capture the duty cycle in microseconds when the PwmOut::write()->pwmout_write() function is called. We do not update the duty cycle when the PwmOut::period_us()->pwmout_period_us() function is called. Before this update, we didn't have the percent value to do so. With this update, the percent value is saved whenever pwmout_write() is called. And the percentage is used, when appropriate, in the pwmout_period_us() function. If the duty cycle is updated with a time value before the pwmout_period_us() function is called, that percentage will not be used.

There are no Greentea or Unittest that cover this functionality. The problem can be observed on the output of the pin. This was manually tested by multiple team members at Infineon.

Impact of changes

Likely none. If there is an impact, it will be positive. The PWM signal will now be correct and as expected after PwmOut::resume() is called.

Migration actions required

Not applicable

Documentation

None

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

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Reviewers

@ARMMbed/team-cypress

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[ciarmcom]

@billwatersiii, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[ifyall]

Approved

[0xc0170]

CI started

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[billwatersiii]

@0xc0170, the checks that are failing don't have anything to do with the one file that I modified in this pull request. Is this something that you can look into and resolve?

[0xc0170]

Yes, looking at it now.

[0xc0170]

There was a fix merged few days back #15138 - can you rebase this pull request? I'll restart testing.

Pull request has been modified.

[billwatersiii]

@0xc0170, the rebase is complete. Please restart testing.

[0xc0170]

Ci restarted

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jenkins-ci/mbed-os-ci_build-cloud-example-ARM	✔️
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jenkins-ci/mbed-os-ci_build-example-GCC_ARM	✔️
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