solitaire-c64/keyboard.c65

#IFNDEF __lib_keyboard
#DEFINE __lib_keyboard 1

GOTO __skip_lib_keyboard

// ============================================================================
// KEYBOARD INPUT DRIVER FOR COMMODORE 64
// ============================================================================
// Direct CIA keyboard matrix reading (no IRQ required)
// Uses non-interfering keyboard scan technique to avoid conflicts with
// joysticks on ports 1 and 2.
//
// Based on code from:
// https://codebase64.c64.org/doku.php?id=base:scanning_the_keyboard_without_joysticks_interfere
//
// This method converts keycodes to row/column values and performs double-check
// scanning to ensure joystick inputs don't interfere with keyboard detection.
//
// Usage:
//   #INCLUDE "keyboard.c65"
//   BYTE key
//   key_scan(key)
//   SWITCH key
//     CASE KEY_F1
//       // handle F1
//     CASE KEY_F3
//       // handle F3
//   ENDSWITCH
// ============================================================================

// CIA Port addresses
WORD CONST CIA_PORTA = $DC00     // Port A - ROW selection (write)
WORD CONST CIA_PORTB = $DC01     // Port B - COLUMN reading (read)
WORD CONST CIA_DDRA = $DC02      // Port A Data Direction Register
WORD CONST CIA_DDRB = $DC03      // Port B Data Direction Register

// Key constants (returned by key_scan)
BYTE CONST KEY_NONE = 0
BYTE CONST KEY_F1 = 1
BYTE CONST KEY_F3 = 2
BYTE CONST KEY_F7 = 3
BYTE CONST KEY_RUNSTOP = 4
BYTE CONST KEY_RETURN = 5

// C64 Keycode constants (for internal use)
// Based on: https://www.c64-wiki.com/wiki/Keyboard
BYTE CONST KEYCODE_RETURN = $01
BYTE CONST KEYCODE_F7F8 = $03
BYTE CONST KEYCODE_F1F2 = $04
BYTE CONST KEYCODE_F3F4 = $05
BYTE CONST KEYCODE_RUNSTOP = $3F

// Row and column lookup tables for keyboard scanning
LABEL key_row_table
ASM
  !8 $FE, $FD, $FB, $F7, $EF, $DF, $BF, $7F
ENDASM

LABEL key_column_table
ASM
  !8 $01, $02, $04, $08, $10, $20, $40, $80
ENDASM

// Key history for debouncing (one byte per tracked key)
BYTE key_history_f1
BYTE key_history_f3
BYTE key_history_f7
BYTE key_history_return
BYTE key_history_runstop

// ============================================================================
// FUNC key_check_raw
// Low-level keyboard check for a specific keycode
// Uses non-interfering scan method with double-check to avoid joystick conflicts
// Returns: result = 1 if pressed, 0 if not pressed
// This comes from here:
// https://codebase64.c64.org/doku.php?id=base:scanning_the_keyboard_without_joysticks_interfere
// ============================================================================
FUNC key_check_raw({BYTE keycode} io:{BYTE histv} out:{BYTE result})
  ASM
    lda |keycode|
    pha
    lsr
    lsr
    lsr
    tay
    lda key_row_table,y
    sta $dc00
    pla
    and #$07
    tay
    lda $dc01
    and key_column_table,y
    bne _nokey
    lda #$ff        ; key is checked 2nd time, to be sure
    sta $dc00       ; joy #1 and #2 are not interfering
    lda $dc01
    and key_column_table,y
    beq _nokey

    cmp |histv|     ; history value?
    bne _newkey
    clc             ; case #3, key is held down. keep history & set C=0
    bcc _backy

_nokey
    asl             ; case #1, no keypress, update history value 2x & set C=0
    clc
    !byte $24       ; BIT zero page - skips next 2-byte instruction
_newkey
    sec             ; case #2, key pressed&released. update history & set C=1
    sta |histv|

_backy
    lda #$ff
    sta $dc00       ; set default value
    lda #$7f
    sta $dc01       ; set default value

    ; Convert carry flag to result: C=1 -> pressed (1), C=0 -> not pressed (0)
    lda #0
    rol             ; shift carry into bit 0
    sta |result|
  ENDASM
FEND


// ============================================================================
// FUNC key_scan
// Scan keyboard and return which key is pressed
// Returns KEY_* constant (KEY_NONE if no relevant key pressed)
// Uses non-interfering keyboard scan to avoid joystick conflicts
// ============================================================================
FUNC key_scan(out:{BYTE key_pressed})
  BYTE check_result

  key_pressed = KEY_NONE

  // Set up DDR: Port A = output (rows), Port B = input (columns)
  ASM
    lda #$ff
    sta $dc02  // CIA_DDRA
    lda #$00
    sta $dc03  // CIA_DDRB
  ENDASM

  // Check F1
  key_check_raw(KEYCODE_F1F2, key_history_f1, check_result)
  IF check_result > 0
    key_pressed = KEY_F1
  ENDIF

  // Check F3
  IF key_pressed == KEY_NONE
    key_check_raw(KEYCODE_F3F4, key_history_f3, check_result)
    IF check_result > 0
      key_pressed = KEY_F3
    ENDIF
  ENDIF

  // Check F7
  IF key_pressed == KEY_NONE
    key_check_raw(KEYCODE_F7F8, key_history_f7, check_result)
    IF check_result > 0
      key_pressed = KEY_F7
    ENDIF
  ENDIF

  // Check RUN/STOP
  IF key_pressed == KEY_NONE
    key_check_raw(KEYCODE_RUNSTOP, key_history_runstop, check_result)
    IF check_result > 0
      key_pressed = KEY_RUNSTOP
    ENDIF
  ENDIF

  // Check RETURN
  IF key_pressed == KEY_NONE
    key_check_raw(KEYCODE_RETURN, key_history_return, check_result)
    IF check_result > 0
      key_pressed = KEY_RETURN
    ENDIF
  ENDIF
FEND


LABEL __skip_lib_keyboard

#IFEND