Interrupt System

Overview

Una Aventura Inesperada uses the Nintendo DS interrupt system for responsive input handling and time-based animations. The game configures three interrupt sources: IRQ_KEYS for player input, IRQ_TIMER0 for dialog debouncing, and IRQ_TIMER1 for sprite animation.

Interrupt Configuration

The ConfigurarInterrupciones() function (main.c:242) sets up all interrupt handlers during initialization:

void ConfigurarInterrupciones() {
    // Enable keyboard interrupts
    irqSet(IRQ_KEYS, TeclasJugador);
    irqEnable(IRQ_KEYS);
    REG_KEYCNT = 0x7FFF;
    
    // Dialog timer (TIMER0)
    irqEnable(IRQ_TIMER0);
    irqSet(IRQ_TIMER0, HabilitarBotonesDialogo);
    TIMER_DATA(0) = 32768;
    TIMER_CR(0) = TIMER_DIV_1024 | TIMER_ENABLE | TIMER_IRQ_REQ;
    timerPause(0);
    
    // Animation timer (TIMER1)
    irqEnable(IRQ_TIMER1);
    irqSet(IRQ_TIMER1, ActualizarAnimacion);
    TIMER_DATA(1) = 32768;
    TIMER_CR(1) = TIMER_DIV_1024 | TIMER_ENABLE | TIMER_IRQ_REQ;
}

IRQ_KEYS: Player Input

Configuration

IRQ_KEYS

Interrupt Source

Triggers when configured buttons are pressed on the DS.

REG_KEYCNT

u16

default:"0x7FFF"

Key interrupt control register. The value 0x7FFF enables interrupts for all buttons.Special values:

0x7FFF - All buttons enabled (during gameplay)
0x3FFF - Reduced button set (during dialogs, main.c:659)

Callback: TeclasJugador()

The TeclasJugador() interrupt handler (main.c:271) processes directional input and handles collision detection:

void TeclasJugador() {
    // UP button (REG_KEYINPUT == 0x03BF)
    if (movimientosJugador > 0 && 
        REG_KEYINPUT == 0x03BF && 
        posJugFila > 0 && 
        esPartidaAcabada == false && 
        mapMemory[(posJugFila-1)*32+posJugColumna] != 18 && 
        mapMemory[(posJugFila-1)*32+posJugColumna] != 28) {
        
        // Box collision at 2 tiles ahead
        if(mapMemory[(posJugFila-2)*32+posJugColumna] == 19) {
            MoverObstaculo(0);
        }
        // Enemy collision (tiles 5 or 42)
        else if(mapMemory[(posJugFila-2)*32+posJugColumna] == 5 || 
                mapMemory[(posJugFila-2)*32+posJugColumna] == 42) {
            int enemActual = -1;
            for (int i=0; i<numeroDeEnemigos && enemActual == -1; i++) {
                if(posJugFila-2 == posicionesEnemigo[i].y && 
                   posJugColumna == posicionesEnemigo[i].x) {
                    enemActual = i;
                }
            }
            MoverEnemigo(0, enemActual);
        }
        
        // If path is clear, move player
        if(mapMemory[(posJugFila-2)*32+posJugColumna] != 19 && 
           mapMemory[(posJugFila-2)*32+posJugColumna] != 5 && 
           puedeJugadorMoverse == true) {
            
            // Restore floor tiles
            mapMemory[(posJugFila)*32+posJugColumna] = 
                ComprobarSuelo((posJugFila)*32+posJugColumna, mapaAcutal);
            mapMemory[(posJugFila)*32+(posJugColumna+1)] = 
                ComprobarSuelo((posJugFila)*32+(posJugColumna+1), mapaAcutal);
            mapMemory[(posJugFila+1)*32+posJugColumna] = 
                ComprobarSuelo((posJugFila+1)*32+posJugColumna, mapaAcutal);
            mapMemory[(posJugFila+1)*32+(posJugColumna+1)] = 
                ComprobarSuelo((posJugFila+1)*32+(posJugColumna+1), mapaAcutal);
            
            posJugFila -= 2; // Move 2 tiles (2x2 sprite)
            
            // Draw player sprite on new position
            pos_mapMemory = posJugFila*32 + posJugColumna;
            mapMemory[pos_mapMemory] = ElegirFondoJugador(0, pos_mapMemory);
            
            pos_mapMemory = posJugFila*32 + (posJugColumna+1);
            mapMemory[pos_mapMemory] = ElegirFondoJugador(1, pos_mapMemory);
            
            pos_mapMemory = (posJugFila+1)*32 + posJugColumna;
            mapMemory[pos_mapMemory] = ElegirFondoJugador(2, pos_mapMemory);
            
            pos_mapMemory = (posJugFila+1)*32 + (posJugColumna+1);
            mapMemory[pos_mapMemory] = ElegirFondoJugador(3, pos_mapMemory);
        }
        
        movimientosJugador--;
        puedeJugadorMoverse = true;
        ActualizarBarraMovimientos();
    }
    // ... similar code for DOWN (0x037F), LEFT (0x03DF), RIGHT (0x03EF)
}

Input Register Values

The REG_KEYINPUT register is checked against specific values to detect directional input:

0x03BF

REG_KEYINPUT value

UP button pressed

0x037F

REG_KEYINPUT value

DOWN button pressed (main.c:323)

0x03DF

REG_KEYINPUT value

LEFT button pressed (main.c:362)

0x03EF

REG_KEYINPUT value

RIGHT button pressed (main.c:399)

The interrupt only fires when REG_KEYCNT is configured. During dialogs, the game sets REG_KEYCNT = 0x3FFF (main.c:659) to disable certain inputs, then restores 0x7FFF when gameplay resumes (main.c:796).

IRQ_TIMER0: Dialog Timing

Purpose

Timer 0 implements input debouncing for dialogs. Without this timer, a single screen touch would advance through all dialogs instantly.

Configuration

irqEnable(IRQ_TIMER0);
irqSet(IRQ_TIMER0, HabilitarBotonesDialogo);
TIMER_DATA(0) = 32768;
TIMER_CR(0) = TIMER_DIV_1024 | TIMER_ENABLE | TIMER_IRQ_REQ;
timerPause(0); // Initially paused

TIMER_DATA(0)

u16

default:"32768"

Initial timer value. The timer counts up from this value to 65535 before overflowing.Calculation:

Clock: BUS_CLOCK / 1024 (see TIMER_DIV_1024)
Ticks until overflow: 65535 - 32768 = 32767
Time: ~0.5 seconds

TIMER_CR(0)

Timer Control

Control flags for Timer 0:

TIMER_DIV_1024 - Divide bus clock by 1024
TIMER_ENABLE - Start the timer
TIMER_IRQ_REQ - Generate interrupt on overflow

Callback: HabilitarBotonesDialogo()

This simple callback (main.c:780) re-enables dialog button input after the debounce delay:

void HabilitarBotonesDialogo() {
    esActivoBotonesDialogos = true;
    timerPause(0);
}

Usage Flow

Dialog opens - CrearDialogo() sets esActivoBotonesDialogos = false (main.c:968)
Player selects option - Touch input is processed
Timer starts - timerUnpause(0) called (main.c:965)
~0.5s later - HabilitarBotonesDialogo() fires, re-enabling buttons
Timer pauses - Ready for next dialog

The timer remains paused between dialogs to conserve CPU cycles. It only runs during the debounce period.

IRQ_TIMER1: Animation Updates

Purpose

Timer 1 drives sprite animation by toggling between two animation frames (F1 and F2) for the player, NPCs, and enemies.

Configuration

irqEnable(IRQ_TIMER1);
irqSet(IRQ_TIMER1, ActualizarAnimacion);
TIMER_DATA(1) = 32768;
TIMER_CR(1) = TIMER_DIV_1024 | TIMER_ENABLE | TIMER_IRQ_REQ;
// No pause - runs continuously during gameplay

TIMER_DATA(1)

u16

default:"32768"

Same timing as Timer 0: ~0.5 seconds per frame, resulting in ~2 FPS animation.

Callback: ActualizarAnimacion()

The ActualizarAnimacion() interrupt handler (main.c:981) updates all sprite animations:

void ActualizarAnimacion() {
    if(esFotograma1Activo == true) {
        // Update NPC to Frame 1 (tiles 38-41)
        pos_mapMemory = posNpcFila*32 + posNpcColumna;
        mapMemory[pos_mapMemory] = 38;
        
        pos_mapMemory = posNpcFila*32 + (posNpcColumna+1);
        mapMemory[pos_mapMemory] = 39;
        
        pos_mapMemory = (posNpcFila+1)*32 + posNpcColumna;
        mapMemory[pos_mapMemory] = 40;
        
        pos_mapMemory = (posNpcFila+1)*32 + (posNpcColumna+1);
        mapMemory[pos_mapMemory] = 41;
        
        // Update all living enemies to Frame 1 (tiles 5, 14-16)
        for(int i = 0; i < numeroDeEnemigos; i++) {
            if(posicionesEnemigo[i].vivo == true) {
                pos_mapMemory = posicionesEnemigo[i].y*32 + posicionesEnemigo[i].x;
                mapMemory[pos_mapMemory] = 5;
                
                pos_mapMemory = posicionesEnemigo[i].y*32 + (posicionesEnemigo[i].x+1);
                mapMemory[pos_mapMemory] = 14;
                
                pos_mapMemory = (posicionesEnemigo[i].y+1)*32 + posicionesEnemigo[i].x;
                mapMemory[pos_mapMemory] = 15;
                
                pos_mapMemory = (posicionesEnemigo[i].y+1)*32 + (posicionesEnemigo[i].x+1);
                mapMemory[pos_mapMemory] = 16;
            }
        }
        esFotograma1Activo = false;
    } else {
        // Update NPC to Frame 2 (tiles 30-33)
        pos_mapMemory = posNpcFila*32 + posNpcColumna;
        mapMemory[pos_mapMemory] = 30;
        
        pos_mapMemory = posNpcFila*32 + (posNpcColumna+1);
        mapMemory[pos_mapMemory] = 31;
        
        pos_mapMemory = (posNpcFila+1)*32 + posNpcColumna;
        mapMemory[pos_mapMemory] = 32;
        
        pos_mapMemory = (posNpcFila+1)*32 + (posNpcColumna+1);
        mapMemory[pos_mapMemory] = 33;
        
        // Update all living enemies to Frame 2 (tiles 42-45)
        for(int i = 0; i < numeroDeEnemigos; i++) {
            if(posicionesEnemigo[i].vivo == true) {
                pos_mapMemory = posicionesEnemigo[i].y*32 + posicionesEnemigo[i].x;
                mapMemory[pos_mapMemory] = 42;
                
                pos_mapMemory = posicionesEnemigo[i].y*32 + (posicionesEnemigo[i].x+1);
                mapMemory[pos_mapMemory] = 43;
                
                pos_mapMemory = (posicionesEnemigo[i].y+1)*32 + posicionesEnemigo[i].x;
                mapMemory[pos_mapMemory] = 44;
                
                pos_mapMemory = (posicionesEnemigo[i].y+1)*32 + (posicionesEnemigo[i].x+1);
                mapMemory[pos_mapMemory] = 45;
            }
        }
        esFotograma1Activo = true;
    }
    
    // Always update player animation (tiles 0/34, 8/35, 9/36, 10/37)
    pos_mapMemory = posJugFila*32 + posJugColumna;
    mapMemory[pos_mapMemory] = ElegirFondoJugador(0, pos_mapMemory);
    
    pos_mapMemory = posJugFila*32 + (posJugColumna+1);
    mapMemory[pos_mapMemory] = ElegirFondoJugador(1, pos_mapMemory);
    
    pos_mapMemory = (posJugFila+1)*32 + posJugColumna;
    mapMemory[pos_mapMemory] = ElegirFondoJugador(2, pos_mapMemory);
    
    pos_mapMemory = (posJugFila+1)*32 + (posJugColumna+1);
    mapMemory[pos_mapMemory] = ElegirFondoJugador(3, pos_mapMemory);
}

Animation Frame Mapping

esFotograma1Activo

bool

Global flag toggled by ActualizarAnimacion() to alternate between Frame 1 and Frame 2.

NPC Animation:

Frame 1: Tiles 38, 39, 40, 41
Frame 2: Tiles 30, 31, 32, 33

Enemy Animation:

Frame 1: Tiles 5, 14, 15, 16
Frame 2: Tiles 42, 43, 44, 45

Player Animation:

Frame 1: Tiles 0/6, 8/11, 9/12, 10/13 (depends on floor type)
Frame 2: Tiles 34, 35, 36, 37

The player’s animation tiles are selected by ElegirFondoJugador() (main.c:464), which chooses different tiles based on the underlying floor type to create composite sprites.

Timer Control

The game pauses and resumes timers to manage performance:

Pausing Timers

timerPause(0);  // Stop dialog timer (main.c:253, 782)
timerPause(1);  // Stop animations during dialogs (main.c:940)

Resuming Timers

timerUnpause(0); // Start dialog debounce (main.c:965)
timerUnpause(1); // Resume animations in gameplay (main.c:794)

Timer 1 is paused during dialogs (main.c:940) to freeze animations and improve performance. It resumes when GenerarNivel() is called (main.c:794).

Interrupt Priorities

The Nintendo DS processes interrupts in hardware-defined priority order:

IRQ_KEYS - Highest priority (immediate input response)
IRQ_TIMER0 - Medium priority (dialog timing)
IRQ_TIMER1 - Lower priority (animations can wait)

In practice, conflicts are rare because:

Input interrupts fire only on button changes
Timers overflow at 0.5-second intervals
Animations update tile indices (fast operation)

Performance Considerations

Interrupt Overhead:

TeclasJugador(): approximately 100-200 cycles (tile map updates)
HabilitarBotonesDialogo(): less than 10 cycles (boolean assignment)
ActualizarAnimacion(): approximately 500-1000 cycles (updates 2-12 sprites)

All interrupts complete well within the 1/60th second frame budget.

Getting Started

Game Design

Development

Technical Reference

Overview

Interrupt Configuration

IRQ_KEYS: Player Input

Configuration

Callback: TeclasJugador()

Input Register Values

IRQ_TIMER0: Dialog Timing

Purpose

Configuration

Callback: HabilitarBotonesDialogo()

Usage Flow

IRQ_TIMER1: Animation Updates

Purpose

Configuration

Callback: ActualizarAnimacion()

Animation Frame Mapping

Timer Control

Pausing Timers

Resuming Timers

Interrupt Priorities

Performance Considerations

Build docs developers (and LLMs) love

Getting Started

Game Design

Development

Technical Reference

​Overview

​Interrupt Configuration

​IRQ_KEYS: Player Input

​Configuration

​Callback: TeclasJugador()

​Input Register Values

​IRQ_TIMER0: Dialog Timing

​Purpose

​Configuration

​Callback: HabilitarBotonesDialogo()

​Usage Flow

​IRQ_TIMER1: Animation Updates

​Purpose

​Configuration

​Callback: ActualizarAnimacion()

​Animation Frame Mapping

​Timer Control

​Pausing Timers

​Resuming Timers

​Interrupt Priorities

​Performance Considerations

Build docs developers (and LLMs) love

Overview

Interrupt Configuration

IRQ_KEYS: Player Input

Configuration

Callback: TeclasJugador()

Input Register Values

IRQ_TIMER0: Dialog Timing

Purpose

Configuration

Callback: HabilitarBotonesDialogo()

Usage Flow

IRQ_TIMER1: Animation Updates

Purpose

Configuration

Callback: ActualizarAnimacion()

Animation Frame Mapping

Timer Control

Pausing Timers

Resuming Timers

Interrupt Priorities

Performance Considerations