RFC: Timer API

[rleh]

Currently the only Timer driver(s) in modm are written for STM32 and the API is very hardware-specific. See e.g. https://docs.modm.io/develop/api/nucleo-g474re/classmodm_1_1platform_1_1Timer8.html

I propose to rename the current API to TimerHal (similar to SpiHal) and to add APIs for different functionalities (PWM generation, encoder input, DC- and BLDC- motors, ...)

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cc @TomSaw @salkinium

[TomSaw]

I suggest two clearly separated, stacked APIs:

Low lvl Timer API - Feature complete

Gives unified, generic access to timers, independent of the MCU nor the MCU-family.
CTC, InputCapture, PWM single-slope, PWM dual-slope, Encoder-input, ...

High lvl Timer API - Application oriented

Inherits or aggregates Low lvl API and feels like a peripheral driver. Like with peripheral drivers, the application-designer don't wants to be confronted with the inner mechanisms and topologies. He/She/It just wants the functionality that makes use of Timers.

Examples

• Instead of exposing Input Capture there are methods like measureFrequency...
• Clear Timer Compare CTC will be configured with methods setFrequency...
• Facade different PWM-Modes (single-slope, dual-slope, ...) behind a unified set of methods. Not sure with this. It may be too much -> the border of simplification