# Backlighting
-Many keyboards support backlit keys by way of individual LEDs placed through or underneath the keyswitches. QMK is able to control the brightness of these LEDs by switching them on and off rapidly in a certain ratio, a technique known as *Pulse Width Modulation*, or PWM. By altering the duty cycle of the PWM signal, it creates the illusion of dimming.
+Many keyboards support backlit keys by way of individual LEDs placed through or underneath the keyswitches. This feature is distinct from both the [RGB underglow](feature_rgblight.md) and [RGB matrix](feature_rgb_matrix.md) features as it usually allows for only a single colour per switch, though you can obviously install multiple different single coloured LEDs on a keyboard.
+
+QMK is able to control the brightness of these LEDs by switching them on and off rapidly in a certain ratio, a technique known as *Pulse Width Modulation*, or PWM. By altering the duty cycle of the PWM signal, it creates the illusion of dimming.
The MCU can only supply so much current to its GPIO pins. Instead of powering the backlight directly from the MCU, the backlight pin is connected to a transistor or MOSFET that switches the power to the LEDs.
-## Usage
+## Driver configuration
Most keyboards have backlighting enabled by default if they support it, but if it is not working for you, check that your `rules.mk` includes the following:
-```make
-BACKLIGHT_ENABLE = yes
+```makefile
+BACKLIGHT_ENABLE = software # Valid driver values are 'yes,software,no'
```
-You should then be able to use the keycodes below to change the backlight level.
+See below for help on individual drivers.
## Keycodes
+Once enabled the following keycodes below can be used to change the backlight level.
|Key |Description |
|---------|------------------------------------------|
|`BL_DEC` |Decrease the backlight level |
|`BL_BRTG`|Toggle backlight breathing |
-## Caveats
+## Backlight Functions
-This feature is distinct from both the [RGB underglow](feature_rgblight.md) and [RGB matrix](feature_rgb_matrix.md) features as it usually allows for only a single colour per switch, though you can obviously use multiple different coloured LEDs on a keyboard.
+|Function |Description |
+|----------|-----------------------------------------------------------|
+|`backlight_toggle()` |Turn the backlight on or off |
+|`backlight_enable()` |Turn the backlight on |
+|`backlight_disable()` |Turn the backlight off |
+|`backlight_step()` |Cycle through backlight levels |
+|`backlight_increase()` |Increase the backlight level |
+|`backlight_decrease()` |Decrease the backlight level |
+|`backlight_level(x)` |Sets the backlight level to specified level |
+|`get_backlight_level()` |Return the current backlight level |
+|`is_backlight_enabled()`|Return whether the backlight is currently on |
-Hardware PWM is only supported on certain pins of the MCU, so if the backlighting is not connected to one of them, a software PWM implementation triggered by hardware timer interrupts will be used.
+### Backlight Breathing Functions
-Hardware PWM is supported according to the following table:
+|Function |Description |
+|----------|---------------------------------------------------|
+|`breathing_toggle()` |Turn the backlight breathing on or off |
+|`breathing_enable()` |Turns on backlight breathing |
+|`breathing_disable()` |Turns off backlight breathing |
-| Backlight Pin | Hardware timer |
-|---------------|-------------------------|
-|`B5` | Timer 1 |
-|`B6` | Timer 1 |
-|`B7` | Timer 1 |
-|`C6` | Timer 3 |
-|`D4` | Timer 1 (ATmega32A only)|
-| other | Software PWM |
+## Common Driver Configuration
-The [audio feature](feature_audio.md) also uses hardware timers. Please refer to the following table to know what hardware timer the software PWM will use depending on the audio configuration:
+To change the behavior of the backlighting, `#define` these in your `config.h`:
-| Audio Pin(s) | Audio Timer | Software PWM Timer |
-|--------------|-------------|--------------------|
-| `C4` | Timer 3 | Timer 1 |
-| `C5` | Timer 3 | Timer 1 |
-| `C6` | Timer 3 | Timer 1 |
-| `B5` | Timer 1 | Timer 3 |
-| `B6` | Timer 1 | Timer 3 |
-| `B7` | Timer 1 | Timer 3 |
-| `Bx` & `Cx` | Timer 1 & 3 | None |
+|Define |Default |Description |
+|---------------------|-------------|--------------------------------------------------------------------------------------|
+|`BACKLIGHT_LEVELS` |`3` |The number of brightness levels (maximum 31 excluding off) |
+|`BACKLIGHT_CAPS_LOCK`|*Not defined*|Enable Caps Lock indicator using backlight (for keyboards without dedicated LED) |
+|`BACKLIGHT_BREATHING`|*Not defined*|Enable backlight breathing, if supported |
+|`BREATHING_PERIOD` |`6` |The length of one backlight "breath" in seconds |
+|`BACKLIGHT_ON_STATE` |`0` |The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low |
-When all timers are in use for [audio](feature_audio.md), the backlight software PWM will not use a hardware timer, but instead will be triggered during the matrix scan. In this case the backlight doesn't support breathing and might show lighting artifacts (for instance flickering), because the PWM computation might not be called with enough timing precision.
+### Backlight On State
-## Configuration
+Most backlight circuits are driven by an N-channel MOSFET or NPN transistor. This means that to turn the transistor *on* and light the LEDs, you must drive the backlight pin, connected to the gate or base, *high*.
+Sometimes, however, a P-channel MOSFET, or a PNP transistor is used. In this case, when the transistor is on, the pin is driven *low* instead.
-To change the behaviour of the backlighting, `#define` these in your `config.h`:
+This functionality is configured at the keyboard level with the `BACKLIGHT_ON_STATE` define.
-|Define |Default |Description |
-|---------------------|-------------|-------------------------------------------------------------------------------------------------------------|
-|`BACKLIGHT_PIN` |`B7` |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
-|`BACKLIGHT_PINS` |*Not defined*|experimental: see below for more information |
-|`BACKLIGHT_LEVELS` |`3` |The number of brightness levels (maximum 15 excluding off) |
-|`BACKLIGHT_CAPS_LOCK`|*Not defined*|Enable Caps Lock indicator using backlight (for keyboards without dedicated LED) |
-|`BACKLIGHT_BREATHING`|*Not defined*|Enable backlight breathing, if supported |
-|`BREATHING_PERIOD` |`6` |The length of one backlight "breath" in seconds |
-|`BACKLIGHT_ON_STATE` |`0` |The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low |
+## AVR driver
-## Backlight On State
+On AVR boards, the default driver currently sniffs the configuration to pick the best scenario. To enable it, add this to your rules.mk:
+```makefile
+BACKLIGHT_ENABLE = yes
+```
+
+### Caveats
+
+Hardware PWM is supported according to the following table:
+
+|Backlight Pin|AT90USB64/128|ATmega16/32U4|ATmega16/32U2|ATmega32A|ATmega328P|
+|-------------|-------------|-------------|-------------|---------|----------|
+|`B1` | | | | |Timer 1 |
+|`B2` | | | | |Timer 1 |
+|`B5` |Timer 1 |Timer 1 | | | |
+|`B6` |Timer 1 |Timer 1 | | | |
+|`B7` |Timer 1 |Timer 1 |Timer 1 | | |
+|`C4` |Timer 3 | | | | |
+|`C5` |Timer 3 | |Timer 1 | | |
+|`C6` |Timer 3 |Timer 3 |Timer 1 | | |
+|`D4` | | | |Timer 1 | |
+|`D5` | | | |Timer 1 | |
+
+All other pins will use software PWM. If the [Audio](feature_audio.md) feature is disabled or only using one timer, the backlight PWM can be triggered by a hardware timer:
+
+|Audio Pin|Audio Timer|Software PWM Timer|
+|---------|-----------|------------------|
+|`C4` |Timer 3 |Timer 1 |
+|`C5` |Timer 3 |Timer 1 |
+|`C6` |Timer 3 |Timer 1 |
+|`B5` |Timer 1 |Timer 3 |
+|`B6` |Timer 1 |Timer 3 |
+|`B7` |Timer 1 |Timer 3 |
-Most backlight circuits are driven by an N-channel MOSFET or NPN transistor. This means that to turn the transistor *on* and light the LEDs, you must drive the backlight pin, connected to the gate or base, *low*.
-Sometimes, however, a P-channel MOSFET, or a PNP transistor is used. In this case you must `#define BACKLIGHT_ON_STATE 1`, so that when the transistor is on, the pin is driven *high* instead.
+When both timers are in use for Audio, the backlight PWM will not use a hardware timer, but will instead be triggered during the matrix scan. In this case, breathing is not supported, and the backlight might flicker, because the PWM computation may not be called with enough timing precision.
-## Multiple backlight pins
+### AVR Configuration
+
+To change the behavior of the backlighting, `#define` these in your `config.h`:
+
+|Define |Default |Description |
+|---------------------|-------------|--------------------------------------------------------------------------------------------------------------|
+|`BACKLIGHT_PIN` |`B7` |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this |
+|`BACKLIGHT_PINS` |*Not defined*|experimental: see below for more information |
+
+### Multiple backlight pins
Most keyboards have only one backlight pin which control all backlight LEDs (especially if the backlight is connected to an hardware PWM pin).
In software PWM, it is possible to define multiple backlight pins. All those pins will be turned on and off at the same time during the PWM duty cycle.
To activate multiple backlight pins, you need to add something like this to your user `config.h`:
-~~~c
+```c
#define BACKLIGHT_LED_COUNT 2
#undef BACKLIGHT_PIN
#define BACKLIGHT_PINS { F5, B2 }
-~~~
+```
-## Hardware PWM Implementation
+### Hardware PWM Implementation
When using the supported pins for backlighting, QMK will use a hardware timer configured to output a PWM signal. This timer will count up to `ICRx` (by default `0xFFFF`) before resetting to 0.
The desired brightness is calculated and stored in the `OCRxx` register. When the counter reaches this value, the backlight pin will go low, and is pulled high again when the counter resets.
The breathing effect is achieved by registering an interrupt handler for `TIMER1_OVF_vect` that is called whenever the counter resets, roughly 244 times per second.
In this handler, the value of an incrementing counter is mapped onto a precomputed brightness curve. To turn off breathing, the interrupt handler is simply disabled, and the brightness reset to the level stored in EEPROM.
-## Software PWM Implementation
+### Timer Assisted PWM Implementation
When `BACKLIGHT_PIN` is not set to a hardware backlight pin, QMK will use a hardware timer configured to trigger software interrupts. This time will count up to `ICRx` (by default `0xFFFF`) before resetting to 0.
When resetting to 0, the CPU will fire an OVF (overflow) interrupt that will turn the LEDs on, starting the duty cycle.
The breathing effect is the same as in the hardware PWM implementation.
-## Backlight Functions
+## ARM Driver
-|Function |Description |
-|----------|-----------------------------------------------------------|
-|`backlight_toggle()` |Turn the backlight on or off |
-|`backlight_enable()` |Turn the backlight on |
-|`backlight_disable()` |Turn the backlight off |
-|`backlight_step()` |Cycle through backlight levels |
-|`backlight_increase()` |Increase the backlight level |
-|`backlight_decrease()` |Decrease the backlight level |
-|`backlight_level(x)` |Sets the backlight level to specified level |
-|`get_backlight_level()` |Return the current backlight level |
-|`is_backlight_enabled()`|Return whether the backlight is currently on |
+While still in its early stages, ARM backlight support aims to eventually have feature parity with AVR. To enable it, add this to your rules.mk:
+```makefile
+BACKLIGHT_ENABLE = yes
+```
-### Backlight Breathing Functions
+### Caveats
+
+Currently only hardware PWM is supported, not timer assisted, and does not provide automatic configuration.
+
+?> STMF072 support is being investigated.
+
+### ARM Configuration
+
+To change the behavior of the backlighting, `#define` these in your `config.h`:
+
+|Define |Default |Description |
+|------------------------|-------------|-------------------------------------------------------------------------------------------------------------|
+|`BACKLIGHT_PIN` |`B7` |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PWM_DRIVER` |`PWMD4` |The PWM driver to use, see ST datasheets for pin to PWM timer mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PWM_CHANNEL` |`3` |The PWM channel to use, see ST datasheets for pin to PWM channel mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PAL_MODE` |`2` |The pin alternative function to use, see ST datasheets for pin AF mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
-|Function |Description |
-|----------|----------------------------------------------------------|
-|`breathing_toggle()` |Turn the backlight breathing on or off |
-|`breathing_enable()` |Turns on backlight breathing |
-|`breathing_disable()` |Turns off backlight breathing |
+## Software PWM Driver
+
+Emulation of PWM while running other keyboard tasks, it offers maximum hardware compatibility without extra platform configuration. The tradeoff is the backlight might jitter when the keyboard is busy. To enable, add this to your rules.mk:
+```makefile
+BACKLIGHT_ENABLE = software
+```
+
+### Software PWM Configuration
+
+To change the behavior of the backlighting, `#define` these in your `config.h`:
+
+|Define |Default |Description |
+|-----------------|-------------|-------------------------------------------------------------------------------------------------------------|
+|`BACKLIGHT_PIN` |`B7` |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PINS` |*Not defined*|experimental: see below for more information |
+
+### Multiple backlight pins
+
+Most keyboards have only one backlight pin which control all backlight LEDs (especially if the backlight is connected to an hardware PWM pin).
+In software PWM, it is possible to define multiple backlight pins. All those pins will be turned on and off at the same time during the PWM duty cycle.
+This feature allows to set for instance the Caps Lock LED (or any other controllable LED) brightness at the same level as the other LEDs of the backlight. This is useful if you have mapped LCTRL in place of Caps Lock and you need the Caps Lock LED to be part of the backlight instead of being activated when Caps Lock is on.
+
+To activate multiple backlight pins, you need to add something like this to your user `config.h`:
+
+```c
+#undef BACKLIGHT_PIN
+#define BACKLIGHT_PINS { F5, B2 }
+```
projects / qmk_firmware.git / blobdiff