Add a button HAL and corresponding drivers

[g-oikonomou]

This pull proposes a platform-independent button API (and corresponding example) that has the following key features:

• Provides a uniform way to determine button-related events (which are no longer a sensors_event).

  • On button press (button_hal_press_event)
  • On button release (button_hal_release_event)
  • On continuous button press, generated with a period of 1 second (button_hal_periodic_event). (I did consider making the period configurable, but I think it's over-design.).

  This allows us to do something on button press, something else on continuous press for 5 seconds, something yet different on release.

• Supports an arbitrary number of buttons.

• Handles software debounce internally, on press as well as on release.

• The PR assumes that a platform already supports the new GPIO HAL. Platform developers/maintainers only need to define their platform's buttons, using a single macro call. Something as simple as:

  BUTTON_HAL_BUTTON(key_left, "Key Left", BOARD_IOID_KEY_LEFT, \
                    GPIO_HAL_PIN_CFG_PULL_UP, BOARD_BUTTON_HAL_INDEX_KEY_LEFT, \
                    true);
  
  BUTTON_HAL_BUTTON(key_right, "Key Right", BOARD_IOID_KEY_RIGHT, \
                    GPIO_HAL_PIN_CFG_PULL_UP, BOARD_BUTTON_HAL_INDEX_KEY_RIGHT, \
                    true);
  

This design brings a number of benefits:

• We expose a simple single button API to examples
• A button is no longer a sensor and therefore not bound to the requirements of the sensors API.
• We no longer make assumptions in os/ as to how many buttons a platform will have, nor of what the symbol names will be.
• We have a single implementation of a s/w debounce, instead of dozens of instances of it. Platform/product developers don't need to spend time understanding/implementing these things.
• Minimizes code duplication: Most current platform button drivers are simply a different platform's driver pasted across.
• All platform buttons support the same features (whereas previously some supported press duration events, some did not).

Platforms currently supported:

• All CC13xx/CC26xx
• All CC2538

[simonduq]

We had a discussion on an earlier version of this branch didn't we? Was trying to find it so we can link to it and followup.

[g-oikonomou]

Closing this till further notice

[g-oikonomou]

I have done a major rework of this pull and I am re-opening it.

Now uses the GPIO HAL, so basically if a device supports the GPIO HAL, it automatically also supports buttons.

I am editing the OP to reflect recent changes.

Tested with Launchpad/CC2650, zoul/firefly, zoul/remote-reva.

More testing to come. Help with testing welcome.

[g-oikonomou]

After a chat with @nfi last night:

• The interrupt handler now just polls a process. Debounce management is scheduled by the process.
• Added a way to retrieve the count of buttons on a device.
• Added a way to retrieve a button by index (0, 1, ... button_hal_button_count - 1).

Tested on launchpad/cc2650 and zoul/remote-reva

[nfi]

I have tested the ipso-object example on Zolertia Firefly with button CoAP notifications up to Leshan and I think everything looks good.

[g-oikonomou]

Can we like merge this? :)

[joakimeriksson]

Yes, let's get it in! I updated branch now - can do the merge after that.