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Diffstat (limited to 'docs/feature_backlight.md')
| -rw-r--r-- | docs/feature_backlight.md | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/docs/feature_backlight.md b/docs/feature_backlight.md index aa747f90e7..97421c0432 100644 --- a/docs/feature_backlight.md +++ b/docs/feature_backlight.md @@ -10,8 +10,30 @@ These keycodes control the backlight. Most keyboards use this for single color i |---------|------------------------------------------| |`BL_TOGG`|Turn the backlight on or off | |`BL_STEP`|Cycle through backlight levels | -|`BL_x` |Set a specific backlight level between 0-9| -|`BL_ON` |An alias for `BL_9` | -|`BL_OFF` |An alias for `BL_0` | +|`BL_ON` |Set backlight to max brightness | +|`BL_OFF` |Turn backlight off | |`BL_INC` |Increase backlight level | |`BL_DEC` |Decrease 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 (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. |