qmk_firmware/keyboards/handwired/trackpoint/keymaps/default/keymap.c

#include QMK_KEYBOARD_H

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    [0] = LAYOUT(
        KC_BTN1,    KC_BTN3,    KC_BTN2
    )
};