qmk_firmware/quantum/process_keycode/process_printer_bb.c

#include "process_printer.h"
#include "action_util.h"

bool printing_enabled = false;
uint8_t character_shift = 0;

#define SERIAL_PIN_DDR DDRD
#define SERIAL_PIN_PORT PORTD
#define SERIAL_PIN_MASK _BV(PD3)
#define SERIAL_DELAY 52

inline static
void serial_delay(void) {
  _delay_us(SERIAL_DELAY);
}

inline static
void serial_high(void) {
  SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
}

inline static
void serial_low(void) {
  SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
}

inline static
void serial_output(void) {
  SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
}


void enabled_printing() {
	printing_enabled = true;
	serial_output();
	serial_high();
}

void disable_printing() {
	printing_enabled = false;
}

uint8_t shifted_numbers[10] = {0x21, 0x40, 0x23, 0x24, 0x25, 0x5E, 0x26, 0x2A, 0x28, 0x29};

// uint8_t keycode_to_ascii[0xFF][2];

// keycode_to_ascii[KC_MINS] = {0x2D, 0x5F};

void print_char(char c) {
  uint8_t b = 8;
  serial_output();
  while( b-- ) {
    if(c & (1 << b)) {
      serial_high();
    } else {
      serial_low();
    }
    serial_delay();
  }
}

void print_string(char c[]) {
	for(uint8_t i = 0; i < strlen(c); i++)
		print_char(c[i]);
}

bool process_printer(uint16_t keycode, keyrecord_t *record) {
	if (keycode == PRINT_ON) {
		enabled_printing();
		return false;
	}
	if (keycode == PRINT_OFF) {
		disable_printing();
		return false;
	}

	if (printing_enabled) {
		switch(keycode) {
			case KC_EXLM ... KC_RPRN:
			case KC_UNDS:
			case KC_PLUS:
			case KC_LCBR:
			case KC_RCBR:
			case KC_PIPE:
			case KC_TILD:
				keycode &= 0xFF;
			case KC_LSFT:
			case KC_RSFT:
				if (record->event.pressed) {
					character_shift++;
				} else {
					character_shift--;
				}
				return false;
			break;
		}

		switch(keycode) {
			case KC_F1:
				if (record->event.pressed) {
					print_string("This is a line of text!\n\n\n");
				}
				return false;
			case KC_ESC:
				if (record->event.pressed) {
					print_char(0x1B);
				}
				return false;
			break;
			case KC_SPC:
				if (record->event.pressed) {
					print_char(0x20);
				}
				return false;
			break;
			case KC_A ... KC_Z:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x41 + (keycode - KC_A));
					} else {
						print_char(0x61 + (keycode - KC_A));
					}
				}
				return false;
			break;
			case KC_1 ... KC_0:
				if (record->event.pressed) {
					if (character_shift) {
							print_char(shifted_numbers[keycode - KC_1]);
					} else {
							print_char(0x30 + ((keycode - KC_1 + 1) % 10));
					}
				}
				return false;
			break;
			case KC_ENT:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x0C);
					} else {
						print_char(0x0A);
					}
				}
				return false;
			break;
			case KC_BSPC:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x18);
					} else {
						print_char(0x1A);
					}
				}
				return false;
			break;
			case KC_DOT:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x3E);
					} else {
						print_char(0x2E);
					}
				}
				return false;
			break;
			case KC_COMM:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x3C);
					} else {
						print_char(0x2C);
					}
				}
				return false;
			break;
			case KC_SLSH:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x3F);
					} else {
						print_char(0x2F);
					}
				}
				return false;
			break;
			case KC_QUOT:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x22);
					} else {
						print_char(0x27);
					}
				}
				return false;
			break;
			case KC_GRV:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x7E);
					} else {
						print_char(0x60);
					}
				}
				return false;
			break;
			case KC_MINS:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x5F);
					} else {
						print_char(0x2D);
					}
				}
				return false;
			break;
			case KC_EQL:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x2B);
					} else {
						print_char(0x3D);
					}
				}
				return false;
			break;
			case KC_LBRC:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x7B);
					} else {
						print_char(0x5B);
					}
				}
				return false;
			break;
			case KC_RBRC:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x7D);
					} else {
						print_char(0x5D);
					}
				}
				return false;
			break;
			case KC_BSLS:
				if (record->event.pressed) {
					if (character_shift) {
						print_char(0x7C);
					} else {
						print_char(0x5C);
					}
				}
				return false;
			break;
		}
	}
	return true;

}