Controller Input Tutorial

This tutorial covers reading SNES controllers including button detection and multi-player support.

SNES Controller Layout

    L                              R
┌───────────────────────────────────────┐
│     ┌───┐                   ┌───┐     │
│     │ ↑ │              (X)  │ X │     │
│ ┌───┼───┼───┐      (Y)   (A)├───┤     │
│ │ ← │   │ → │ [SEL][STA] │ Y │ A │    │
│ └───┼───┼───┘            ├───┼───┤    │
│     │ ↓ │                │ B │        │
│     └───┘                └───┘        │
└───────────────────────────────────────┘

Button Constants

OpenSNES defines these button masks in input.h:

// D-Pad
#define KEY_UP      0x0800
#define KEY_DOWN    0x0400
#define KEY_LEFT    0x0200
#define KEY_RIGHT   0x0100
 
// Face Buttons
#define KEY_A       0x0080
#define KEY_B       0x8000
#define KEY_X       0x0040
#define KEY_Y       0x4000
 
// Shoulder Buttons
#define KEY_L       0x0020
#define KEY_R       0x0010
 
// Start/Select
#define KEY_START   0x1000
#define KEY_SELECT  0x2000

Reading Controllers

Direct Register Access (Recommended)

#include <snes.h>
 
u16 pad;
 
while (1) {
    WaitForVBlank();
 
    // Wait for auto-joypad read to complete
    while (REG_HVBJOY & 0x01) {}
 
    // Read controller 1
    pad = REG_JOY1L | (REG_JOY1H << 8);
 
    // Check for disconnected controller
    if (pad == 0xFFFF) {
        // No controller connected
        continue;
    }
 
    // Check buttons
    if (pad & KEY_A) {
        // A button pressed
    }
    if (pad & KEY_UP) {
        // D-pad up pressed
    }
}

Reading Controller 2

u16 pad1, pad2;
 
// Wait for auto-joypad
while (REG_HVBJOY & 0x01) {}
 
// Read both controllers
pad1 = REG_JOY1L | (REG_JOY1H << 8);
pad2 = REG_JOY2L | (REG_JOY2H << 8);

Edge Detection

Detect button presses (not just held state):

u16 pad_current;
u16 pad_previous = 0;
u16 pad_pressed;
 
while (1) {
    WaitForVBlank();
    while (REG_HVBJOY & 0x01) {}
 
    // Read current state
    pad_current = REG_JOY1L | (REG_JOY1H << 8);
 
    // Detect new presses (down this frame, not last frame)
    pad_pressed = pad_current & ~pad_previous;
 
    // Save for next frame
    pad_previous = pad_current;
 
    // Skip if disconnected
    if (pad_current == 0xFFFF) {
        pad_pressed = 0;
    }
 
    // Now use pad_pressed for one-shot actions
    if (pad_pressed & KEY_A) {
        // A was just pressed (fires once)
        player_jump();
    }
 
    // Use pad_current for continuous actions
    if (pad_current & KEY_RIGHT) {
        // Right is held (fires every frame)
        player_x++;
    }
}

Movement Example

u16 player_x = 128;
u16 player_y = 112;
 
void update_player(u16 pad) {
    // Movement with boundary checking
    if (pad & KEY_UP) {
        if (player_y > 0) player_y--;
    }
    if (pad & KEY_DOWN) {
        if (player_y < 224) player_y++;
    }
    if (pad & KEY_LEFT) {
        if (player_x > 0) player_x--;
    }
    if (pad & KEY_RIGHT) {
        if (player_x < 248) player_x++;
    }
}

Two-Player Example

// Player positions
u16 p1_x = 64, p1_y = 112;
u16 p2_x = 192, p2_y = 112;
 
while (1) {
    WaitForVBlank();
    while (REG_HVBJOY & 0x01) {}
 
    // Read both controllers
    u16 pad1 = REG_JOY1L | (REG_JOY1H << 8);
    u16 pad2 = REG_JOY2L | (REG_JOY2H << 8);
 
    // Player 1 movement
    if (pad1 != 0xFFFF) {
        if (pad1 & KEY_UP)    { if (p1_y > 0) p1_y--; }
        if (pad1 & KEY_DOWN)  { if (p1_y < 224) p1_y++; }
        if (pad1 & KEY_LEFT)  { if (p1_x > 0) p1_x--; }
        if (pad1 & KEY_RIGHT) { if (p1_x < 248) p1_x++; }
    }
 
    // Player 2 movement
    if (pad2 != 0xFFFF) {
        if (pad2 & KEY_UP)    { if (p2_y > 0) p2_y--; }
        if (pad2 & KEY_DOWN)  { if (p2_y < 224) p2_y++; }
        if (pad2 & KEY_LEFT)  { if (p2_x > 0) p2_x--; }
        if (pad2 & KEY_RIGHT) { if (p2_x < 248) p2_x++; }
    }
 
    // Update sprites
    oamSet(0, p1_x, p1_y, 0, 0, 0, 0);  // Player 1
    oamSet(1, p2_x, p2_y, 0, 0, 0, 1);  // Player 2
    oamUpdate();
}

Button Combinations

// Check for multiple buttons
if ((pad & KEY_A) && (pad & KEY_B)) {
    // A + B pressed together
}
 
// Check for button + direction
if ((pad & KEY_A) && (pad & KEY_DOWN)) {
    // Down + A (e.g., slide attack)
}
 
// Create combo masks
#define COMBO_HADOUKEN (KEY_DOWN | KEY_RIGHT | KEY_A)
if ((pad & COMBO_HADOUKEN) == COMBO_HADOUKEN) {
    // All combo buttons pressed
}

Menu Navigation

u8 menu_selection = 0;
const u8 MENU_ITEMS = 4;
 
if (pad_pressed & KEY_UP) {
    if (menu_selection > 0) {
        menu_selection--;
    }
}
if (pad_pressed & KEY_DOWN) {
    if (menu_selection < MENU_ITEMS - 1) {
        menu_selection++;
    }
}
if (pad_pressed & KEY_A) {
    // Confirm selection
    activate_menu_item(menu_selection);
}
if (pad_pressed & KEY_B) {
    // Cancel / go back
    close_menu();
}

Hardware Registers

For reference, the joypad registers:

Register	Address	Description
REG_JOY1L	$4218	Controller 1, low byte
REG_JOY1H	$4219	Controller 1, high byte
REG_JOY2L	$421A	Controller 2, low byte
REG_JOY2H	$421B	Controller 2, high byte
REG_JOY3L	$421C	Controller 3 (multitap)
REG_JOY3H	$421D	Controller 3 (multitap)
REG_JOY4L	$421E	Controller 4 (multitap)
REG_JOY4H	$421F	Controller 4 (multitap)
REG_HVBJOY	$4212	Status (bit 0 = auto-read busy)

Tips

1. Always wait for auto-joypad - Check REG_HVBJOY & 0x01 before reading
2. Check for disconnected controllers - 0xFFFF means no controller
3. Use edge detection for menus - Prevents rapid-fire selection
4. Use held state for movement - Smoother continuous motion

Example

See examples/input/two_players/ for a complete two-player demo.

Next Steps

• Audio & Music
• Input API Reference