Add 'capslock backlight' feature to Iron180

[Gondolindrim]

Description

Some Iron180 users have shown interest in only having the caps lock LED soldered and for it to work as a caps lock indicator.

This PR adds a CAPSLOCK_BACKLIGHT define in config.h which in turn enables a led state function in iron180.c that toggles backlight and breathing according to caps lock. The PR also contains README instructions.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[zvecr]

Any reason to go custom over cores BACKLIGHT_CAPS_LOCK implementation?

[Gondolindrim]

Any reason to go custom over cores BACKLIGHT_CAPS_LOCK implementation?

As far as I tested, BACKLIGHT_CAPS_LOCK does not play well with breathing: it works fine for static light but if breathing is on, the LEDs keep on breathing no matter the state of caps lock. This is also reproduced using the controls in VIA. The code of the PR handles breathing properly (then again, as far as I tested).

[fauxpark]

That sounds like something that should be fixed in core code, rather than reimplemented here.

[Gondolindrim]

That sounds like something that should be fixed in core code, rather than reimplemented here.

I DM'd @zvecr at length about this. The thing is, the core code implementation's intent is to treat breathing as a different state than backlight itself; in other words, breathing is not supposed to be turned on and off when backlight is respectively enabled or disabled because they are supposed to be two different features.

Now since zvecr is a developer and a key member I took his statement as a somewhat "official" QMK opinion on it. However, the intended effect I want for Iron180 is for breathing to be turned on and off with the backlight, hence why the keyboard-level implementation in favour of the core-level implementation.

So in this discussion me and zvecr agreed that maybe we ought to leave the core implementation as it is; the discussion now is what would be the best way to implement this feature in the keyboard-level. According to zvecr the functions I used, videlicet, backlight_enable(), backlight_disable(), breathing_enable() and breathing_disable() will write to EEPROM, hence the way it is implemented now will operate EEPROM every time caps lock is pressed which would not be a particular problem were Iron180 not powered by STM32F072 which uses the EEPROM simulation in flash, potentially wearing flash. Maybe I should, instead of enable-disable, just operate with backlight and breathing brightness or levels?

EDIT: typos