#include "tusb.h"

// Device Descriptor
tusb_desc_device_t const desc_device = {
    .bLength            = sizeof(tusb_desc_device_t),
    .bDescriptorType    = TUSB_DESC_DEVICE,
    .bcdUSB             = 0x0200,
    .bDeviceClass       = 0x00,
    .bDeviceSubClass    = 0x00,
    .bDeviceProtocol    = 0x00,
    .bMaxPacketSize0    = CFG_TUD_ENDPOINT0_SIZE,
    .idVendor           = 0xCafe,   // Your Vendor ID
    .idProduct          = 0x4001,   // Your Product ID
    .bcdDevice          = 0x0100,
    .iManufacturer      = 0x01,
    .iProduct           = 0x02,
    .iSerialNumber      = 0x03,
    .bNumConfigurations = 0x01
};

uint8_t const * tud_descriptor_device_cb(void) {
    return (uint8_t const *) &desc_device;
}

// Configuration Descriptor (MIDI)
enum { ITF_NUM_MIDI = 0, ITF_NUM_MIDI_STREAMING, ITF_NUM_TOTAL };
#define CONFIG_TOTAL_LEN  (TUD_CONFIG_DESC_LEN + TUD_MIDI_DESC_LEN)
#define EPNUM_MIDI_IN     0x01
#define EPNUM_MIDI_OUT    0x01

uint8_t const desc_configuration[] = {
    TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, 0x00, 100),
    TUD_MIDI_DESCRIPTOR(ITF_NUM_MIDI, 0, EPNUM_MIDI_OUT, (0x80 | EPNUM_MIDI_IN), 64)
};

uint8_t const * tud_descriptor_configuration_cb(uint8_t index) {
    return desc_configuration;
}

// String Descriptors (The source of your error)
char const* string_desc_arr[] = {
    (const char[]) { 0x09, 0x04 }, // 0: Supported language is English
    "Raspberry Pi",                // 1: Manufacturer
    "Go Volta Lights",            // 2: Product
    "123456",                      // 3: Serial
};

static uint16_t _desc_str[32];

uint16_t const* tud_descriptor_string_cb(uint8_t index, uint16_t langid) {
    (void) langid;
    uint8_t chr_count;

    if (index == 0) {
        memcpy(&_desc_str[1], string_desc_arr[0], 2);
        chr_count = 1;
    } else {
        if (!(index < sizeof(string_desc_arr)/sizeof(string_desc_arr[0]))) return NULL;
        const char* str = string_desc_arr[index];
        chr_count = strlen(str);
        if (chr_count > 31) chr_count = 31;
        for(uint8_t i=0; i<chr_count; i++) _desc_str[1+i] = str[i];
    }

    _desc_str[0] = (TUSB_DESC_STRING << 8 ) | (2*chr_count + 2);
    return _desc_str;
}