There are a lot of hidden functions in QMK that are incredible useful, or may add a bit of functionality that you've been wanting. Functions that are specific to certain features are not included here, as those will be on their respective feature page.
The first is the `update_tri_layer(x, y, z)` function. This function check to see if layers `x` and `y` are both on. If they are both on, then it turns on layer `z`. Otherwise, if both `x` and `y` are not both on (either only one is, or neither is), then it turns off layer `z`.
The other function is `update_tri_layer_state(state, x, y, z)`. This function is meant to be called from the [`layer_state_set_*` functions](custom_quantum_functions.md#layer-change-code). This means that any time that you use a keycode to change the layer, this will be checked. So you could use `LT(layer, kc)` to change the layer and it will trigger the same layer check.
1. You cannot access the `z` layer without having `x` and `y` layers on, since if you try to activate just layer `z`, it will run this code and turn off layer `z` before you could use it.
2. Because layers are processed from the highest number `z` should be a higher layer than `x` and `y` or you may not be able to access it.
Alternatively, you don't have to immediately "return" the value. This is useful if you want to add multiple tri layers, or if you want to add additional effects.
To use this, you would use `set_single_persistent_default_layer(layer)`. If you have a name defined for your layer, you can use that instead (such as _QWERTY, _DVORAK or _COLEMAK).
This will set the default layer, update the persistent settings, and play a tune if you have [Audio](feature_audio.md) enabled on your board, and the default layer sounds set.
?> There are a large number of predefined songs in [quantum/audio/song_list.h](https://github.com/qmk/qmk_firmware/blob/master/quantum/audio/song_list.h) that you can use.
There is the `RESET` quantum keycode that you can use. But if you want to reset the board as part of a macro, rather than hitting a key separately, you can do that.
If you're having issues with Audio, RGB Underglow, backlighting or keys acting weird, then you can reset the EEPROM (persistent setting storage). To force an EEPROM reset, use the [`EEP_RST` keycode](quantum_keycodes.md) or [Bootmagic Lite](feature_bootmagic.md) functionality. If neither of those are an option, then you can use a custom macro to do so.
If you want to send a random character to the host computer, you can use the `tap_random_base64()` function. This [pseudorandomly](https://en.wikipedia.org/wiki/Pseudorandom_number_generator) selects a number between 0 and 63, and then sends a key press based on that selection. (0–25 is `A`–`Z`, 26–51 is `a`–`z`, 52–61 is `0`–`9`, 62 is `+` and 63 is `/`).