А как, собственно, различить USB CDC устройства?

#define DEVICE_DESCRIPTOR               0x100
#define CONFIGURATION_DESCRIPTOR        0x200
#define STRING_LANG_DESCRIPTOR          0x300
#define STRING_MAN_DESCRIPTOR           0x301
#define STRING_PROD_DESCRIPTOR          0x302
#define STRING_SN_DESCRIPTOR            0x303
#define DEVICE_QUALIFIER_DESCRIPTOR     0x600

...         /*Interface Descriptor */
        0x09, /* bLength: Interface Descriptor size */
        0x04, /* bDescriptorType: Interface */
        0x00, /* bInterfaceNumber: Number of Interface */
        0x00, /* bAlternateSetting: Alternate setting */
        0x03, /* bNumEndpoints: 3 endpoints used */
        0xff, /* bInterfaceClass */
        0x00, /* bInterfaceSubClass */
        0x00, /* bInterfaceProtocol */
        iINTERFACE_DESCR, /* iInterface: */
...

#define LANG_US (uint16_t*)0x0409
 
typedef struct{
    uint8_t  bLength;
    uint8_t  bDescriptorType;
    uint16_t *bString;
} string_descriptor_t;
 
#define _USB_STRING_(name, str) string_descriptor_t name = {sizeof(name), STRING_DESCRIPTOR, str}
 
...
_USB_STRING_(LD, LANG_US);
_USB_STRING_(SD, u"0.0.1");
_USB_STRING_(MD, u"Prolific Technology Inc.");
_USB_STRING_(PD, u"USB-Serial Controller");
_USB_STRING_(ID, u"nitrogen_flooding");
static string_descriptor_t const *StringDescriptor[iDESCR_AMOUNT] = {
    [iLANGUAGE_DESCR] = &LD,
    [iMANUFACTURER_DESCR] = &MD,
    [iPRODUCT_DESCR] = &PD,
    [iSERIAL_DESCR] = &SD,
    [iINTERFACE_DESCR] = &ID
};

#define LANG_US (uint16_t)0x0409
#define _USB_STRING_(name, str)                  \
static const struct name \
{                          \
        uint8_t  bLength;                       \
        uint8_t  bDescriptorType;               \
        uint16_t bString[(sizeof(str) - 2) / 2]; \
    \
} \
name = {sizeof(name), 0x03, str}
 
#define _USB_LANG_ID_(name, lng_id)     \
    \
static const struct name \
{         \
        uint8_t  bLength;         \
        uint8_t  bDescriptorType; \
        uint16_t bString;         \
    \
} \
name = {0x04, 0x03, lng_id}
 
...
 
_USB_LANG_ID_(LD, LANG_US);
_USB_STRING_(SD, u"0.0.1");
_USB_STRING_(MD, u"Prolific Technology Inc.");
_USB_STRING_(PD, u"USB-Serial Controller");
_USB_STRING_(ID, u"nitrogen_flooding");
static void const *StringDescriptor[iDESCR_AMOUNT] = {
    [iLANGUAGE_DESCR] = &LD,
    [iMANUFACTURER_DESCR] = &MD,
    [iPRODUCT_DESCR] = &PD,
    [iSERIAL_DESCR] = &SD,
    [iINTERFACE_DESCR] = &ID
};

static inline void get_descriptor(){
    uint8_t descrtype = setup_packet->wValue >> 8,
            descridx = setup_packet->wValue & 0xff;
    switch(descrtype){
        case DEVICE_DESCRIPTOR:
            wr0(USB_DeviceDescriptor, sizeof(USB_DeviceDescriptor));
        break;
        case CONFIGURATION_DESCRIPTOR:
            wr0(USB_ConfigDescriptor, sizeof(USB_ConfigDescriptor));
        break;
        case STRING_DESCRIPTOR:
            if(descridx < iDESCR_AMOUNT) wr0((const uint8_t *)StringDescriptor[descridx], *((uint8_t*)StringDescriptor[descridx]));
            else EP_WriteIRQ(0, (uint8_t*)0, 0);
        break;
        case DEVICE_QUALIFIER_DESCRIPTOR:
            wr0(USB_DeviceQualifierDescriptor, USB_DeviceQualifierDescriptor[0]);
        break;
        default:
        break;
    }
}