forked from mfulz_github/qmk_firmware
40 lines
2.2 KiB
Markdown
40 lines
2.2 KiB
Markdown
# Backlighting
|
|
|
|
<!-- FIXME: Describe how backlighting works in QMK -->
|
|
|
|
## Backlight Keycodes
|
|
|
|
These keycodes control the backlight. Most keyboards use this for single color in-switch lighting.
|
|
|
|
|Key |Description |
|
|
|---------|------------------------------------------|
|
|
|`BL_TOGG`|Turn the backlight on or off |
|
|
|`BL_STEP`|Cycle through backlight levels |
|
|
|`BL_ON` |Set the backlight to max brightness |
|
|
|`BL_OFF` |Turn the backlight off |
|
|
|`BL_INC` |Increase the backlight level |
|
|
|`BL_DEC` |Decrease the backlight level |
|
|
|`BL_BRTG`|Toggle backlight breathing |
|
|
|
|
Note that for backlight breathing, you need to have `#define BACKLIGHT_BREATHING` in your config.h.
|
|
|
|
## Configuration Options in `config.h`
|
|
|
|
* `BACKLIGHT_PIN B7` defines the pin that controlls the LEDs. Unless you design your own keyboard, you don't need to set this.
|
|
* `BACKLIGHT_LEVELS 3` defines the number of brightness levels (maximum 15 excluding off).
|
|
* `BACKLIGHT_BREATHING` if defined, enables backlight breathing. Note that this is only available if `BACKLIGHT_PIN` is B5, B6 or B7.
|
|
* `BREATHING_PERIOD 6` defines the length of one backlight "breath" in seconds.
|
|
|
|
## Notes on Implementation
|
|
|
|
To change the brightness when using pins B5, B6 or B7, the PWM (Pulse Width Modulation) functionality of the on-chip timer is used.
|
|
The timer is a counter that counts up to a certain TOP value (`0xFFFF` set in ICR1) before resetting to 0.
|
|
We also set an OCR1x register.
|
|
When the counter reaches the value stored in that register, the PWM pin drops to low.
|
|
The PWM pin is pulled high again when the counter resets to 0.
|
|
Therefore, OCR1x basically sets the duty cycle of the LEDs and as such the brightness where `0` is the darkest and `0xFFFF` the brightest setting.
|
|
|
|
To enable the breathing effect, we register an interrupt handler to be called whenever the counter resets (with `ISR(TIMER1_OVF_vect)`).
|
|
In this handler, which gets called roughly 244 times per second, we compute the desired brightness using a precomputed brightness curve.
|
|
To disable breathing, we can just disable the respective interrupt vector and reset the brightness to the desired level.
|