usb_descriptors.c

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2026 Chris Burton
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

#include "tusb.h"

extern char usb_serial[];

#define USB_VID   0x3171
#define USB_PID   0x0071
#define USB_BCD   0x0200

//--------------------------------------------------------------------+
// Device Descriptors
//--------------------------------------------------------------------+
tusb_desc_device_t const desc_device = {
	.bLength            = sizeof(tusb_desc_device_t),
	.bDescriptorType    = TUSB_DESC_DEVICE,
	.bcdUSB             = USB_BCD,

	.bDeviceClass       = TUSB_CLASS_MISC,
	.bDeviceSubClass    = MISC_SUBCLASS_COMMON,
	.bDeviceProtocol    = MISC_PROTOCOL_IAD,

	.bMaxPacketSize0    = CFG_TUD_ENDPOINT0_SIZE,
	.idVendor           = USB_VID,
	.idProduct          = USB_PID,
	.bcdDevice          = 0x0100,
	.iManufacturer      = 0x01,
	.iProduct           = 0x02,
	.iSerialNumber      = 0x03,

	.bNumConfigurations = 0x01
};

// Invoked when received GET DEVICE DESCRIPTOR
// Application return pointer to descriptor
uint8_t const * tud_descriptor_device_cb(void) {
	return (uint8_t const *) &desc_device;
}

//--------------------------------------------------------------------+
// Configuration Descriptor
//--------------------------------------------------------------------+
enum {
	ITF_NUM_MSC = 0,
	ITF_NUM_TOTAL
};

#define CONFIG_TOTAL_LEN  (TUD_CONFIG_DESC_LEN + TUD_MSC_DESC_LEN)
#define EPNUM_MSC_OUT     0x01
#define EPNUM_MSC_IN      0x81

uint8_t const desc_fs_configuration[] = {
	// Config number, interface count, string index, total length, attribute, power in mA
	TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),

	TUD_MSC_DESCRIPTOR(ITF_NUM_MSC, 0, EPNUM_MSC_OUT, EPNUM_MSC_IN, 64)
};

// Invoked when received GET CONFIGURATION DESCRIPTOR
// Application return pointer to descriptor
// Descriptor contents must exist long enough for transfer to complete
uint8_t const * tud_descriptor_configuration_cb(__unused uint8_t index) {
    return desc_fs_configuration;
}

//--------------------------------------------------------------------+
// String Descriptors
//--------------------------------------------------------------------+

// array of pointer to string descriptors
char const* string_desc_arr [] = {
	(const char[]) { 0x09, 0x04 },        // 0: is supported language is English (0x0409)
	"8086 Consultancy",                   // 1: Manufacturer
	"MSC I2C 24C32",                      // 2: Product
	usb_serial,                           // 3: Serial (flash chip ID)
};

static uint16_t _desc_str[32];

// Invoked when received GET STRING DESCRIPTOR request
// Application return pointer to descriptor, whose contents must exist long enough for transfer to complete
uint16_t const* tud_descriptor_string_cb(uint8_t index, __unused uint16_t langid) {
	uint8_t chr_count;

	if ( index == 0) {
		memcpy(&_desc_str[1], string_desc_arr[0], 2);
		chr_count = 1;
	} else {
		// Note: the 0xEE index string is a Microsoft OS 1.0 Descriptors.
		// https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/microsoft-defined-usb-descriptors

		if ( !(index < sizeof(string_desc_arr)/sizeof(string_desc_arr[0])) ) return NULL;

		const char* str = string_desc_arr[index];

		// Cap at max char
		chr_count = (uint8_t) strlen(str);
		if ( chr_count > 31 ) chr_count = 31;

		// Convert ASCII string into UTF-16
		for(uint8_t i=0; i<chr_count; i++) {
			_desc_str[1+i] = str[i];
		}
	}

	// first byte is length (including header), second byte is string type
	_desc_str[0] = (TUSB_DESC_STRING << 8 ) | (2*chr_count + 2);

	return _desc_str;
}