Document EventFlags wait function timeout units

[sarahmarshy]

Description

The EventFlags class does not specify a unit of time for its timeout.

• wait_all
• wait_any

I tried to follow the callstack, but I didn't find the units for this timeout.

Issue request type

[ ] Question
[ X] Enhancement
[ ] Bug

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-203

[kjbracey]

Possible that this carries through a lot of stuff - many descriptions in the rtos namespace including that are cut-and-paste from CMSIS-RTOS documentation following that form.

Basic rule is that every time specified in the rtos namespace is in CMSIS-RTOS "ticks", which CMSIS-RTOS never defines itself. But for Mbed OS we have specified that the RTOS tick is a millisecond (see Kernel::get_ms_count()).

I see some things like ThisThread::flags_wait_all_for have the same wording, but changed the variable name to millisec, which seems like it might do?

Also, the fact that it's "ticks" is also significant - waiting for 5 ticks will take 4.000 to 5.000 milliseconds, depending on phase relative to the next tick. It doesn't aim for precisely 5 millisecond duration (unlike wait_us(5000).

[0Grit]

#9077

[kegilbert]

@sarahmarshy #9670

The above PR should have addressed this, let me know if you have remaining concerns for this issue! Otherwise it should be good to close.