### Initialize and Use Socket Networking with libctru

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes the SOC service with a provided buffer and size, enabling BSD-style socket networking. Demonstrates getting local IP info, performing DNS lookups, and establishing a basic TCP connection.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>

#define SOC_ALIGN 0x1000
#define SOC_BUFFERSIZE 0x100000

static u32* socBuffer;

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Allocate buffer for SOC service
    socBuffer = (u32*)memalign(SOC_ALIGN, SOC_BUFFERSIZE);
    if (!socBuffer) {
        printf("Failed to allocate SOC buffer\n");
        return 1;
    }

    Result res = socInit(socBuffer, SOC_BUFFERSIZE);
    if (R_FAILED(res)) {
        printf("socInit failed: %08lX\n", res);
        free(socBuffer);
        return 1;
    }

    // Get local IP info
    struct in_addr ip, netmask, broadcast;
    SOCU_GetIPInfo(&ip, &netmask, &broadcast);
    printf("IP: %s\n", inet_ntoa(ip));
    printf("Netmask: %s\n", inet_ntoa(netmask));

    // DNS lookup example
    struct hostent* host = gethostbyname("example.com");
    if (host) {
        printf("\nexample.com resolves to:\n");
        for (int i = 0; host->h_addr_list[i]; i++) {
            struct in_addr addr;
            memcpy(&addr, host->h_addr_list[i], sizeof(addr));
            printf("  %s\n", inet_ntoa(addr));
        }
    }

    // Simple TCP connection example
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock >= 0) {
        struct sockaddr_in server;
        server.sin_family = AF_INET;
        server.sin_port = htons(80);
        server.sin_addr = *(struct in_addr*)host->h_addr_list[0];

        if (connect(sock, (struct sockaddr*)&server, sizeof(server)) == 0) {
            const char* request = "GET / HTTP/1.0\r\nHost: example.com\r\n\r\n";
            send(sock, request, strlen(request), 0);

            char buffer[1024];
            int received = recv(sock, buffer, sizeof(buffer) - 1, 0);
            if (received > 0) {
                buffer[received] = '\0';
                printf("\nResponse (first %d bytes):\n%.200s...\n", received, buffer);
            }
        }
        close(sock);
    }

    printf("\nPress START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    socExit();
    free(socBuffer);
    gfxExit();
    return 0;
}

```

--------------------------------

### Perform HTTP GET Request with libctru

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes the HTTP client service and performs a GET request to a specified URL. Handles response status, downloads content, and frees allocated memory. Requires httpcInit before use and httpcExit upon completion.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>

Result httpGet(const char* url, u8** outData, u32* outSize) {
    httpcContext context;
    Result res;

    res = httpcOpenContext(&context, HTTPC_METHOD_GET, url, 0);
    if (R_FAILED(res)) return res;

    // Add headers
    httpcAddRequestHeaderField(&context, "User-Agent", "3DS-Homebrew/1.0");
    httpcAddRequestHeaderField(&context, "Connection", "close");

    // Start request
    res = httpcBeginRequest(&context);
    if (R_FAILED(res)) {
        httpcCloseContext(&context);
        return res;
    }

    // Get response code
    u32 statusCode;
    res = httpcGetResponseStatusCode(&context, &statusCode);
    if (R_FAILED(res) || statusCode != 200) {
        httpcCloseContext(&context);
        return res;
    }

    // Get content size
    u32 contentSize;
    res = httpcGetDownloadSizeState(&context, NULL, &contentSize);

    // Download data
    u8* buffer = (u8*)malloc(contentSize + 1);
    u32 downloadedSize;
    res = httpcDownloadData(&context, buffer, contentSize, &downloadedSize);
    buffer[downloadedSize] = '\0';

    *outData = buffer;
    *outSize = downloadedSize;

    httpcCloseContext(&context);
    return res;
}

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Initialize services
    Result res = httpcInit(0);
    if (R_FAILED(res)) {
        printf("httpcInit failed: %08lX\n", res);
        return 1;
    }

    printf("Fetching data...\n");

    u8* data;
    u32 size;
    res = httpGet("http://example.com/", &data, &size);

    if (R_SUCCEEDED(res)) {
        printf("Downloaded %lu bytes:\n\n", size);
        // Print first 500 chars
        printf("%.500s...\n", (char*)data);
        free(data);
    } else {
        printf("Request failed: %08lX\n", res);
    }

    printf("\nPress START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    httpcExit();
    gfxExit();
    return 0;
}

```

--------------------------------

### IPC Header Parsing Example Output

Source: https://github.com/devkitpro/libctru/wiki/IPC-command-headers

This is an example output from the IPCParseHeader tool, demonstrating how a raw hexadecimal IPC header value is translated into its constituent parts: command ID, normal parameters, and translate parameters, along with the corresponding IPC_MakeHeader function call.

```text
$>IPCParseHeader 0x080b0102
0x80B0102 =>
        id: 0x80B
        normal: 4
        translate: 2
IPC_MakeHeader(0x80B,4,2); // 0x80B0102

```

--------------------------------

### Initialize Graphics Subsystem (gfxInit)

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes the graphics subsystem for both screens with default or custom settings. Use this to set up framebuffers, enable stereoscopic 3D, and manage display modes. Requires including <3ds.h>.

```c
#include <3ds.h>

int main(int argc, char* argv[]) {
    // Initialize with default settings (BGR8 format, double buffering)
    gfxInitDefault();

    // Alternative: Custom initialization with specific formats
    // gfxInit(GSP_RGBA8_OES, GSP_BGR8_OES, false);

    // Enable stereoscopic 3D on the top screen
    gfxSet3D(true);

    // Enable 800px wide mode (New 3DS only, non-square pixels)
    // gfxSetWide(true);

    // Main loop
    while (aptMainLoop()) {
        hidScanInput();
        u32 kDown = hidKeysDown();

        if (kDown & KEY_START) break;

        // Get framebuffer for rendering
        u16 width, height;
        u8* fb = gfxGetFramebuffer(GFX_TOP, GFX_LEFT, &width, &height);

        // Clear to black (framebuffer is in portrait orientation)
        memset(fb, 0, width * height * 3);

        // Flush and swap buffers
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}
```

--------------------------------

### Initialize and use sockets in libctru

Source: https://github.com/devkitpro/libctru/wiki/Networking

Demonstrates the lifecycle of the SOC service, including memory allocation for the buffer and socket cleanup.

```c
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <3ds.h>

int main()
{
    // Initialize graphics and console
    gfxInitDefault();
    gfxSet3D(false);
    consoleInit(GFX_BOTTOM, NULL);

    // Initialize SOC
    SOC_Initialize((u32*)memalign(0x1000, 0x128000), 0x128000);

    // Do networking stuff
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    // ...
    close(sockfd);

    // Cleanup SOC
    SOC_Shutdown();

    return 0
}
```

--------------------------------

### Initialize Console Text Output (consoleInit)

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes a console for stdio-like text output on a specified screen, supporting ANSI color codes and cursor positioning. Requires including <3ds.h> and <stdio.h>.

```c
#include <3ds.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();

    // Initialize console on bottom screen
    PrintConsole* console = consoleInit(GFX_BOTTOM, NULL);

    // Use ANSI color codes
    printf(CONSOLE_RED "Red text\n" CONSOLE_RESET);
    printf(CONSOLE_GREEN "Green text\n" CONSOLE_RESET);
    printf(CONSOLE_CYAN "Cyan text\n" CONSOLE_RESET);

    // Position cursor at row 10, column 5
    printf("\x1b[10;5HPositioned text");

    // Clear screen
    // consoleClear();

    // Create a custom window region
    consoleSetWindow(console, 2, 2, 36, 20);
    printf("Text inside window region\n");

    // Enable debug output to console
    consoleDebugInit(debugDevice_CONSOLE);
    fprintf(stderr, "Debug message\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;

        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}
```

--------------------------------

### Initialize and Use Software Keyboard for Text Input

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes the software keyboard for normal text input, sets hint text and buttons, and captures user input. Handles both successful input and cancellation.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    char inputBuffer[256];

    // Basic text input
    SwkbdState swkbd;
    swkbdInit(&swkbd, SWKBD_TYPE_NORMAL, 2, 255);
    swkbdSetHintText(&swkbd, "Enter your name");
    swkbdSetButton(&swkbd, SWKBD_BUTTON_LEFT, "Cancel", false);
    swkbdSetButton(&swkbd, SWKBD_BUTTON_RIGHT, "OK", true);
    swkbdSetFeatures(&swkbd, SWKBD_PREDICTIVE_INPUT | SWKBD_DARKEN_TOP_SCREEN);

    SwkbdButton button = swkbdInputText(&swkbd, inputBuffer, sizeof(inputBuffer));

    if (button == SWKBD_BUTTON_RIGHT) {
        printf("You entered: %s\n\n", inputBuffer);
    } else {
        printf("Input cancelled\n\n");
    }

    // Numpad input
    SwkbdState numpad;
    swkbdInit(&numpad, SWKBD_TYPE_NUMPAD, 1, 4);
    swkbdSetHintText(&numpad, "Enter PIN");
    swkbdSetPasswordMode(&numpad, SWKBD_PASSWORD_HIDE_DELAY);
    swkbdSetValidation(&numpad, SWKBD_FIXEDLEN, 0, 0);
    swkbdSetNumpadKeys(&numpad, '-', '.');

    button = swkbdInputText(&numpad, inputBuffer, sizeof(inputBuffer));

    if (button != SWKBD_BUTTON_NONE) {
        printf("PIN entered: %s\n\n", inputBuffer);
    }

    // Input with validation callback
    SwkbdState validated;
    swkbdInit(&validated, SWKBD_TYPE_QWERTY, 2, 32);
    swkbdSetHintText(&validated, "Enter email");
    swkbdSetValidation(&validated, SWKBD_NOTEMPTY_NOTBLANK,
                       SWKBD_FILTER_AT, 0); // Disallow @ (just for demo)

    button = swkbdInputText(&validated, inputBuffer, sizeof(inputBuffer));

    SwkbdResult result = swkbdGetResult(&validated);
    if (result == SWKBD_BANNED_INPUT) {
        printf("Input was filtered!\n");
    } else if (button != SWKBD_BUTTON_NONE) {
        printf("Email: %s\n", inputBuffer);
    }

    printf("\nPress START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}

```

--------------------------------

### Create and Manage Threads with threadCreate

Source: https://context7.com/devkitpro/libctru/llms.txt

Demonstrates spawning worker threads, using LightLock for thread-safe data access, and cleaning up resources with threadJoin and threadFree.

```c
#include <3ds.h>
#include <stdio.h>

volatile bool threadRunning = true;
volatile int counter = 0;
LightLock counterLock;

void workerThread(void* arg) {
    int threadId = (int)(intptr_t)arg;

    while (threadRunning) {
        LightLock_Lock(&counterLock);
        counter++;
        int localCounter = counter;
        LightLock_Unlock(&counterLock);

        // Simulate work
        svcSleepThread(100000000LL); // 100ms
    }

    threadExit(threadId); // Exit with thread ID as return code
}

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    LightLock_Init(&counterLock);

    // Create worker thread
    // Priority 0x30 is standard, lower = higher priority
    // Core -2 = default core from exheader
    Thread thread1 = threadCreate(workerThread, (void*)1, 4 * 1024, 0x30, -2, false);
    Thread thread2 = threadCreate(workerThread, (void*)2, 4 * 1024, 0x30, -2, false);

    if (!thread1 || !thread2) {
        printf("Failed to create threads\n");
        return 1;
    }

    printf("Threads created\n");
    printf("Press START to stop\n\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;

        LightLock_Lock(&counterLock);
        printf("\x1b[5;1HCounter: %d    ", counter);
        LightLock_Unlock(&counterLock);

        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    // Signal threads to stop
    threadRunning = false;

    // Wait for threads to finish
    threadJoin(thread1, U64_MAX);
    threadJoin(thread2, U64_MAX);

    // Get exit codes
    printf("\nThread 1 exit code: %d\n", threadGetExitCode(thread1));
    printf("Thread 2 exit code: %d\n", threadGetExitCode(thread2));

    // Clean up
    threadFree(thread1);
    threadFree(thread2);

    gfxExit();
    return 0;
}
```

--------------------------------

### Filesystem Operations with libctru

Source: https://context7.com/devkitpro/libctru/llms.txt

Demonstrates file operations using both standard C I/O (sdmc:/) and low-level FSUSER APIs. Ensure the filesystem service is initialized or auto-initialized.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // FS is auto-initialized, but can be explicit
    // fsInit();

    // Method 1: Using standard C file I/O (sdmc:/ device)
    FILE* file = fopen("sdmc:/test.txt", "w");
    if (file) {
        fprintf(file, "Hello from 3DS!\n");
        fclose(file);
        printf("File written successfully\n");
    }

    // Method 2: Using low-level FS API
    FS_Archive sdmcArchive;
    Result res = FSUSER_OpenArchive(&sdmcArchive, ARCHIVE_SDMC, fsMakePath(PATH_EMPTY, ""));

    if (R_SUCCEEDED(res)) {
        Handle fileHandle;
        FS_Path filePath = fsMakePath(PATH_ASCII, "/data.bin");

        // Create and write file
        res = FSUSER_OpenFile(&fileHandle, sdmcArchive, filePath,
                              FS_OPEN_CREATE | FS_OPEN_WRITE, 0);
        if (R_SUCCEEDED(res)) {
            const char* data = "Binary data";
            u32 bytesWritten;
            FSFILE_Write(fileHandle, &bytesWritten, 0, data, strlen(data), FS_WRITE_FLUSH);
            FSFILE_Close(fileHandle);
            printf("Wrote %lu bytes\n", bytesWritten);
        }

        // Read file
        res = FSUSER_OpenFile(&fileHandle, sdmcArchive, filePath, FS_OPEN_READ, 0);
        if (R_SUCCEEDED(res)) {
            char buffer[256];
            u32 bytesRead;
            FSFILE_Read(fileHandle, &bytesRead, 0, buffer, sizeof(buffer));
            FSFILE_Close(fileHandle);
            buffer[bytesRead] = '\0';
            printf("Read: %s\n", buffer);
        }

        // Get SD card free space
        u64 freeBytes;
        FSUSER_GetFreeBytes(&freeBytes, sdmcArchive);
        printf("Free space: %llu MB\n", freeBytes / (1024 * 1024));

        FSUSER_CloseArchive(sdmcArchive);
    }

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}

```

--------------------------------

### Implement Synchronization with Lightweight Primitives

Source: https://context7.com/devkitpro/libctru/llms.txt

Shows usage of LightLock, CondVar, LightEvent, and LightSemaphore to coordinate threads without consuming kernel handles.

```c
#include <3ds.h>
#include <stdio.h>

LightLock mutex;
RecursiveLock recursiveMutex;
CondVar condVar;
LightEvent event;
LightSemaphore semaphore;

void producerThread(void* arg) {
    for (int i = 0; i < 5; i++) {
        svcSleepThread(500000000LL); // 500ms

        LightLock_Lock(&mutex);
        printf("Producer: item %d ready\n", i);
        CondVar_Signal(&condVar);
        LightLock_Unlock(&mutex);
    }

    // Signal completion
    LightEvent_Signal(&event);
    threadExit(0);
}

void consumerThread(void* arg) {
    for (int i = 0; i < 5; i++) {
        LightLock_Lock(&mutex);
        CondVar_Wait(&condVar, &mutex);
        printf("Consumer: got item %d\n", i);
        LightLock_Unlock(&mutex);
    }
    threadExit(0);
}

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Initialize synchronization primitives
    LightLock_Init(&mutex);
    RecursiveLock_Init(&recursiveMutex);
    CondVar_Init(&condVar);
    LightEvent_Init(&event, RESET_ONESHOT);
    LightSemaphore_Init(&semaphore, 3, 3); // 3 permits

    // Demonstrate semaphore
    printf("Semaphore demo:\n");
    LightSemaphore_Acquire(&semaphore, 1);
    printf("Acquired 1 permit\n");
    LightSemaphore_Acquire(&semaphore, 2);
    printf("Acquired 2 permits\n");

    if (LightSemaphore_TryAcquire(&semaphore, 1) != 0) {
        printf("Cannot acquire more (expected)\n");
    }

    LightSemaphore_Release(&semaphore, 3);
    printf("Released all permits\n\n");

    // Producer-consumer demo
    printf("Producer-Consumer demo:\n");
    Thread producer = threadCreate(producerThread, NULL, 4 * 1024, 0x30, -2, false);
    Thread consumer = threadCreate(consumerThread, NULL, 4 * 1024, 0x30, -2, false);

    // Wait for producer to signal completion
    LightEvent_Wait(&event);
    printf("\nProduction complete!\n");

    threadJoin(producer, U64_MAX);
    threadJoin(consumer, U64_MAX);
    threadFree(producer);
    threadFree(consumer);

    printf("\nPress START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}
```

--------------------------------

### Mount and Access RomFS Files

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes RomFS, mounts the application's RomFS, reads a file, and lists directory contents. Ensure RomFS is properly embedded in your application.

```c
#include <3ds.h>
#include <stdio.h>
#include <dirent.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Mount the application's RomFS as "romfs:/"
    Result res = romfsInit();
    if (R_FAILED(res)) {
        printf("romfsInit failed: %08lX\n", res);
    } else {
        printf("RomFS mounted successfully\n\n");

        // Read a file from RomFS
        FILE* file = fopen("romfs:/data/config.txt", "r");
        if (file) {
            char buffer[256];
            while (fgets(buffer, sizeof(buffer), file)) {
                printf("%s", buffer);
            }
            fclose(file);
        }

        // List directory contents
        DIR* dir = opendir("romfs:/");
        if (dir) {
            printf("\nRomFS contents:\n");
            struct dirent* entry;
            while ((entry = readdir(dir)) != NULL) {
                printf("  %s%s\n", entry->d_name,
                       entry->d_type == DT_DIR ? "/" : "");
            }
            closedir(dir);
        }

        // Mount RomFS from another title
        // romfsMountFromTitle(0x0004000000001234ULL, MEDIATYPE_SD, "other");
        // FILE* f = fopen("other:/file.txt", "r");

        romfsExit();
    }

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}

```

--------------------------------

### Play a 440Hz Tone with NDSP

Source: https://context7.com/devkitpro/libctru/llms.txt

Initializes NDSP, configures audio channels, and plays a continuous 440Hz sine wave tone. Requires linear memory allocation for audio buffers.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>

#define SAMPLE_RATE 22050
#define SAMPLES_PER_BUF (SAMPLE_RATE / 30)

s16* audioBuffer;
ndspWaveBuf waveBuf[2];
int fillBlock = 0;

void fillAudioBuffer(s16* buffer, size_t samples) {
    static float phase = 0;
    float freq = 440.0f; // A4 note

    for (size_t i = 0; i < samples; i++) {
        buffer[i] = (s16)(sinf(phase) * 0x7000);
        phase += 2.0f * M_PI * freq / SAMPLE_RATE;
        if (phase > 2.0f * M_PI) phase -= 2.0f * M_PI;
    }
    DSP_FlushDataCache(buffer, samples * sizeof(s16));
}

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Initialize NDSP
    Result res = ndspInit();
    if (R_FAILED(res)) {
        printf("ndspInit failed: %08lX\n", res);
        return 1;
    }

    // Allocate audio buffer in linear memory
    audioBuffer = (s16*)linearAlloc(SAMPLES_PER_BUF * sizeof(s16) * 2);

    // Configure NDSP
    ndspSetOutputMode(NDSP_OUTPUT_STEREO);
    ndspSetMasterVol(1.0f);

    // Configure channel 0
    ndspChnReset(0);
    ndspChnSetInterp(0, NDSP_INTERP_LINEAR);
    ndspChnSetRate(0, SAMPLE_RATE);
    ndspChnSetFormat(0, NDSP_FORMAT_MONO_PCM16);

    // Set channel volume (left, right, etc.)
    float mix[12] = {1.0f, 1.0f, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
    ndspChnSetMix(0, mix);

    // Initialize wave buffers
    memset(waveBuf, 0, sizeof(waveBuf));
    waveBuf[0].data_vaddr = audioBuffer;
    waveBuf[0].nsamples = SAMPLES_PER_BUF;
    waveBuf[1].data_vaddr = audioBuffer + SAMPLES_PER_BUF;
    waveBuf[1].nsamples = SAMPLES_PER_BUF;

    // Fill initial buffers
    fillAudioBuffer(audioBuffer, SAMPLES_PER_BUF);
    fillAudioBuffer(audioBuffer + SAMPLES_PER_BUF, SAMPLES_PER_BUF);

    // Queue both buffers
    ndspChnWaveBufAdd(0, &waveBuf[0]);
    ndspChnWaveBufAdd(0, &waveBuf[1]);

    printf("Playing 440Hz tone\n");
    printf("Press START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;

        // Refill completed buffers
        if (waveBuf[fillBlock].status == NDSP_WBUF_DONE) {
            fillAudioBuffer((s16*)waveBuf[fillBlock].data_vaddr, SAMPLES_PER_BUF);
            ndspChnWaveBufAdd(0, &waveBuf[fillBlock]);
            fillBlock = !fillBlock;
        }

        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    ndspChnWaveBufClear(0);
    linearFree(audioBuffer);
    ndspExit();
    gfxExit();
    return 0;
}

```

--------------------------------

### Register APT Hook for System Events

Source: https://context7.com/devkitpro/libctru/llms.txt

Registers a callback function to handle APT events like suspend, restore, sleep, and wake-up. Ensures the hook is unregistered before exiting.

```c
#include <3ds.h>
#include <stdio.h>

// Hook callback for APT events
void aptHookCallback(APT_HookType hookType, void* param) {
    switch (hookType) {
        case APTHOOK_ONSUSPEND:
            printf("App suspended\n");
            break;
        case APTHOOK_ONRESTORE:
            printf("App restored\n");
            break;
        case APTHOOK_ONSLEEP:
            printf("System sleeping\n");
            break;
        case APTHOOK_ONWAKEUP:
            printf("System woke up\n");
            break;
        case APTHOOK_ONEXIT:
            printf("App exiting\n");
            break;
        default:
            break;
    }
}

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Register APT hook
    aptHookCookie cookie;
    aptHook(&cookie, aptHookCallback, NULL);

    // Configure sleep behavior
    aptSetSleepAllowed(true);

    // Allow HOME button (can be disabled for critical operations)
    aptSetHomeAllowed(true);

    // Check if running on New 3DS
    bool isNew3DS = false;
    APT_CheckNew3DS(&isNew3DS);
    printf("Running on %s 3DS\n", isNew3DS ? "New" : "Old");

    // Set CPU time limit (for using system core)
    // APT_SetAppCpuTimeLimit(30); // 30% of system core

    printf("\nAPT demo - Press START to exit\n");
    printf("Try pressing HOME button\n");

    while (aptMainLoop()) {
        hidScanInput();
        u32 kDown = hidKeysDown();

        if (kDown & KEY_START) break;

        // Check various APT states
        if (aptCheckHomePressRejected()) {
            printf("HOME press was blocked\n");
        }

        // Active state check
        printf("\x1b[8;1HApp active: %s  ", aptIsActive() ? "yes" : "no");

        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    // Unhook before exit
    aptUnhook(&cookie);

    gfxExit();
    return 0;
}

```

--------------------------------

### Allocate and manage hardware-accessible memory in C

Source: https://context7.com/devkitpro/libctru/llms.txt

Demonstrates the usage of linearAlloc, vramAlloc, and mappableAlloc for hardware-specific memory requirements. Always flush the data cache before GPU access when using linear memory.

```c
#include <3ds.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Allocate linear memory (for GPU textures, audio buffers, etc.)
    size_t size = 256 * 256 * 4; // RGBA texture
    void* linearBuffer = linearAlloc(size);

    if (linearBuffer) {
        printf("Linear buffer allocated: %p\n", linearBuffer);
        printf("Size: %zu bytes\n", linearGetSize(linearBuffer));

        // Get physical address (needed for GPU commands)
        u32 physAddr = osConvertVirtToPhys(linearBuffer);
        printf("Physical address: %08lX\n", physAddr);

        // Use the memory
        memset(linearBuffer, 0xFF, size);

        // Flush data cache before GPU access
        GSPGPU_FlushDataCache(linearBuffer, size);

        linearFree(linearBuffer);
        printf("Linear buffer freed\n\n");
    }

    // Allocate VRAM (video memory for framebuffers/textures)
    void* vramBuffer = vramAlloc(64 * 64 * 2); // RGB565 texture
    if (vramBuffer) {
        printf("VRAM buffer allocated: %p\n", vramBuffer);
        printf("VRAM size: %zu bytes\n", vramGetSize(vramBuffer));
        vramFree(vramBuffer);
        printf("VRAM buffer freed\n\n");
    }

    // Allocate mappable memory (for shared memory with services)
    void* mappableBuffer = mappableAlloc(0x1000);
    if (mappableBuffer) {
        printf("Mappable buffer allocated: %p\n", mappableBuffer);
        mappableFree(mappableBuffer);
        printf("Mappable buffer freed\n");
    }

    printf("\nPress START to exit\n");

    while (aptMainLoop()) {
        hidScanInput();
        if (hidKeysDown() & KEY_START) break;
        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    gfxExit();
    return 0;
}
```

--------------------------------

### Parse and Create IPC Command Headers (C)

Source: https://github.com/devkitpro/libctru/wiki/IPC-command-headers

This C code defines the IPC_MakeHeader function for creating IPC command headers and includes a main function that parses a raw header value from command-line arguments, displays its components, and reconstructs it using IPC_MakeHeader. It also asserts that the parsed components correctly reconstruct the original header.

```c
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

typedef uint8_t u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;

/**
 * @brief Command header to be used for IPC
 * @param normal_params    Size of the normal parameters in words. Up to 63.
 * @param translate_params Size of the translate parameters in words. Up to 63.
 *
 * Normal parameters are sent directly to the process while the translate parameters might go through modifications and checks by the kernel.
 * The translate parameters are described by headers generated with the IPC_Desc_* functions.
 *
 * @note While #normal_params is equivalent to the number of normal parameters, #translate_params includes the size occupied by the translate parameters headers.
 */
static inline u32 IPC_MakeHeader(u16 command_id, unsigned normal_params, unsigned translate_params)
{
	return ((u32) command_id << 16) | (((u32) normal_params & 0x3F) << 6) | (((u32) translate_params & 0x3F) << 0);
}


int main(int argc, char* argv[])
{
    assert(argc == 2);
    unsigned header = (unsigned)strtol(argv[1], NULL, 0);
    
    unsigned id = header>>16;
    unsigned normal =header >> 6 & 0x3F;
    unsigned translate = header&0x3F;
    printf("0x%X =>\n"
                   "\tid: 0x%X\n"
                   "\tnormal: %d\n"
                   "\ttranslate: %d\n"
            ,header,id,normal,translate );
    printf("IPC_MakeHeader(0x%X,%d,%d); // 0x%X\n"
            ,id,normal,translate,header);
    assert(header == IPC_MakeHeader(id,normal,translate));
    return 0;
}

```

--------------------------------

### Scan and Read Input with libctru

Source: https://context7.com/devkitpro/libctru/llms.txt

Scans and reads various input states including buttons, Circle Pad, touchscreen, accelerometer, and gyroscope. Ensure HID services are enabled and configured before use.

```c
#include <3ds.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
    gfxInitDefault();
    consoleInit(GFX_BOTTOM, NULL);

    // Enable accelerometer and gyroscope
    HIDUSER_EnableAccelerometer();
    HIDUSER_EnableGyroscope();

    // Configure key repeat for menu navigation
    hidSetRepeatParameters(25, 5);

    while (aptMainLoop()) {
        hidScanInput();

        // Get button states
        u32 kDown = hidKeysDown();       // Just pressed this frame
        u32 kHeld = hidKeysHeld();       // Currently held
        u32 kUp = hidKeysUp();           // Just released
        u32 kRepeat = hidKeysDownRepeat(); // With key repeat

        if (kDown & KEY_START) break;

        // Read Circle Pad position (-156 to +156 range)
        circlePosition circlePos;
        hidCircleRead(&circlePos);

        // Read touchscreen
        touchPosition touchPos;
        if (kHeld & KEY_TOUCH) {
            hidTouchRead(&touchPos);
            printf("\x1b[5;1HTouch: X=%3d Y=%3d  ", touchPos.px, touchPos.py);
        }

        // Read accelerometer
        accelVector accel;
        hidAccelRead(&accel);

        // Read gyroscope
        angularRate gyro;
        hidGyroRead(&gyro);

        consoleClear();
        printf("Circle Pad: X=%4d Y=%4d\n", circlePos.dx, circlePos.dy);
        printf("Accel: X=%4d Y=%4d Z=%4d\n", accel.x, accel.y, accel.z);
        printf("Gyro:  X=%4d Y=%4d Z=%4d\n", gyro.x, gyro.y, gyro.z);
        printf("\nButtons: %08lX\n", kHeld);

        if (kDown & KEY_A) printf("A pressed!\n");
        if (kDown & KEY_B) printf("B pressed!\n");
        if (kDown & KEY_X) printf("X pressed!\n");
        if (kDown & KEY_Y) printf("Y pressed!\n");

        gfxFlushBuffers();
        gfxSwapBuffers();
        gspWaitForVBlank();
    }

    HIDUSER_DisableAccelerometer();
    HIDUSER_DisableGyroscope();
    gfxExit();
    return 0;
}

```

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