qmk_firmware/docs/custom_matrix.md

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# Custom Matrix
QMK provides a mechanism to supplement or replace the default matrix scanning routine with your own code.
The reasons to use this feature include:
* Extra hardware between the keyboard's switches and MCU pins
* I/O multiplexer
* Line decoder
* Irregular switch matrix
* Simultaneous use of `COL2ROW` and `ROW2COL`
## Prerequisites
Implementing custom matrix usually involves compilation of an additional source file. It is recommended that for consistency, this file is called `matrix.c`.
Add a new file to your keyboard directory:
```
keyboards/<keyboard>/matrix.c
```
And to configure compilation for the new file, add this to your `rules.mk`:
```make
SRC += matrix.c
```
## 'lite'
Provides a default implementation for various scanning functions, reducing the boilerplate code when implementing custom matrix.
To configure it, add this to your `rules.mk`:
```make
CUSTOM_MATRIX = lite
```
And implement the following functions in a `matrix.c` file in your keyboard folder:
```c
void matrix_init_custom(void) {
// TODO: initialize hardware here
}
bool matrix_scan_custom(matrix_row_t current_matrix[]) {
bool matrix_has_changed = false;
// TODO: add matrix scanning routine here
return matrix_has_changed;
}
```
## Full Replacement
When more control over the scanning routine is required, you can choose to implement the full scanning routine.
To configure it, add this to your rules.mk:
```make
CUSTOM_MATRIX = yes
```
And implement the following functions in a `matrix.c` file in your keyboard folder:
```c
matrix_row_t matrix_get_row(uint8_t row) {
// TODO: return the requested row data
}
void matrix_print(void) {
// TODO: use print() to dump the current matrix state to console
}
void matrix_init(void) {
// TODO: initialize hardware and global matrix state here
// Unless hardware debouncing - Init the configured debounce routine
debounce_init(MATRIX_ROWS);
// This *must* be called for correct keyboard behavior
matrix_init_kb();
}
uint8_t matrix_scan(void) {
bool changed = false;
// TODO: add matrix scanning routine here
// Unless hardware debouncing - use the configured debounce routine
changed = debounce(raw_matrix, matrix, MATRIX_ROWS, changed);
// This *must* be called for correct keyboard behavior
matrix_scan_kb();
return changed;
}
```
And also provide defaults for the following callbacks:
```c
__attribute__((weak)) void matrix_init_kb(void) { matrix_init_user(); }
__attribute__((weak)) void matrix_scan_kb(void) { matrix_scan_user(); }
__attribute__((weak)) void matrix_init_user(void) {}
__attribute__((weak)) void matrix_scan_user(void) {}
```