# List of Useful Core Functions To Make Your Keyboard Better
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.
## (OLKB) Tri Layers
There are actually separate functions that you can use there, depending on what you're after.
### `update_tri_layer(x, y, z)`
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 runs on layer `z`. Otherwise, if both `x` and `y` are not both on (either only one is, or neither is), then it runs off layer `z`.
This function is useful if you want to create specific keys that have this functionality, but other layer keycodes won't do this.
#### Example
```c
bool process_record_user(uint16_t keycode, keyrecord_t *record) {
switch (keycode) {
case LOWER:
if (record->event.pressed) {
layer_on(_LOWER);
update_tri_layer(_LOWER, _RAISE, _ADJUST);
} else {
layer_off(_LOWER);
update_tri_layer(_LOWER, _RAISE, _ADJUST);
}
return false;
break;
case RAISE:
if (record->event.pressed) {
layer_on(_RAISE);
update_tri_layer(_LOWER, _RAISE, _ADJUST);
} else {
layer_off(_RAISE);
update_tri_layer(_LOWER, _RAISE, _ADJUST);
}
return false;
break;
}
return true;
}
```
### `update_tri_layer_state(state, x, y, z)`
The other function is `update_tri_layer_state(state, x, y, z)`. This function is meant to be called from they [`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.
The caveat to this method is that 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.
#### Example
```c
uint32_t layer_state_set_user(uint32_t state) {
return update_tri_layer_state(state, _LOWER, _RAISE, _ADJUST);
}
```
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.
```c
uint32_t layer_state_set_user(uint32_t state) {
state = update_tri_layer_state(state, _LOWER, _RAISE, _ADJUST);
state = update_tri_layer_state(state, _RAISE, _SYMB, _SPECIAL);
return state;
}
```
## Setting the Persistent Default Layer
Do you want to set the default layer, so that it's retained even after you unplug the board? If so, this is the function for you.
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.
To configure the default layer sounds, you would want to define this in your `config.h` file, like this:
```c
#define DEFAULT_LAYER_SONGS { SONG(QWERTY_SOUND), \
SONG(COLEMAK_SOUND), \
SONG(DVORAK_SOUND) \
}
```
?> 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.
## Reseting the keyboard
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.
And to do so, add `reset_keyboard()` to your function or macro, and this will reset to bootloader.
## Wiping the EEPROM (Persistent Storage)
If you're having issues with Audio, RGB Underglow, backlighting or keys acting weird, then you can reset the EEPROM (persistent setting storage). Bootmagic is one way to do this, but if that isn't enabled, then you can use a custom macro to do so.
To wipe the EEPROM, run `eeconfig_init()` from your function or macro to reset most of the settings to default.
## Tap random key
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 `/`).
?> Needless to say, but this is _not_ a cryptographically secure method of generating random Base64 keys or passwords.
## Software Timers
It's possible to start timers and read values for time-specific events. Here's an example:
```c
static uint16_t key_timer;
key_timer = timer_read();
if (timer_elapsed(key_timer) < 100) {
// do something if less than 100ms have passed
} else {
// do something if 100ms or more have passed
}
```
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/*
ChibiOS - Copyright (C) 2006..2018 Giovanni Di Sirio
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
/**
* @file memstreams.c
* @brief Memory streams code.
*
* @addtogroup memory_streams
* @{
*/
#include <string.h>
#include "hal.h"
#include "memstreams.h"
/*===========================================================================*/
/* Driver local definitions. */
/*===========================================================================*/
/*===========================================================================*/
/* Driver exported variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Driver local variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Driver local functions. */
/*===========================================================================*/
static size_t _writes(void *ip, const uint8_t *bp, size_t n) {
MemoryStream *msp = ip;
if (msp->size - msp->eos < n)
n = msp->size - msp->eos;
memcpy(msp->buffer + msp->eos, bp, n);
msp->eos += n;
return n;
}
static size_t _reads(void *ip, uint8_t *bp, size_t n) {
MemoryStream *msp = ip;
if (msp->eos - msp->offset < n)
n = msp->eos - msp->offset;
memcpy(bp, msp->buffer + msp->offset, n);
msp->offset += n;
return n;
}
static msg_t _put(void *ip, uint8_t b) {
MemoryStream *msp = ip;
if (msp->size - msp->eos <= 0)
return MSG_RESET;
*(msp->buffer + msp->eos) = b;
msp->eos += 1;
return MSG_OK;
}
static msg_t _get(void *ip) {
uint8_t b;
MemoryStream *msp = ip;
if (msp->eos - msp->offset <= 0)
return MSG_RESET;
b = *(msp->buffer + msp->offset);
msp->offset += 1;
return b;
}
static const struct MemStreamVMT vmt = {_writes, _reads, _put, _get};
/*===========================================================================*/
/* Driver exported functions. */
/*===========================================================================*/
/**
* @brief Memory stream object initialization.
*
* @param[out] msp pointer to the @p MemoryStream object to be initialized
* @param[in] buffer pointer to the memory buffer for the memory stream
* @param[in] size total size of the memory stream buffer
* @param[in] eos initial End Of Stream offset. Normally you need to
* put this to zero for RAM buffers or equal to @p size
* for ROM streams.
*/
void msObjectInit(MemoryStream *msp, uint8_t *buffer,
size_t size, size_t eos) {
msp->vmt = &vmt;
msp->buffer = buffer;
msp->size = size;
msp->eos = eos;
msp->offset = 0;
}
/** @} */
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