Zephyr USB device string descriptors definition

Question

the question is about USB device implementation in Zephyr OS. We need to add interface string descriptor for ineterface name. Using USBD_STRING_DESCR_DEFINE(primary) I've added that to string descriptor section, but it has index "0" - that's wrong (?) because it brakes basic string descriptor structure defined in usb_descriptor.c. How we could setup defines/linker commands to add new USB strings after that ones in usb_descriptor.c? Given example defines newly added string with index 0 (but it should be 4 - after manufacturer, product and serial num).

USBD_STRING_DESCR_DEFINE(primary) struct webusb_iface_descriptor webusb_string_descr = {
    /* webusb iface String Descriptor */
    .bLength = sizeof(struct webusb_iface_descriptor),
    .bDescriptorType = USB_DESC_STRING,
    .bString = WEBUSB_IFNAME,
};

void webusb_init() 
{
    int idx = usb_get_str_descriptor_idx(&webusb_string_descr);
    if (idx != 0) {
        webusb_desc.if0.iInterface = idx;
    }
} 

Answer 1

You should use USBD_STRING_DESCR_USER_DEFINE rather than USBD_STRING_DESCR_DEFINE. ...USER_DEFINE will add to the descriptors and ...DESC_DEFINE will override the default ones that are included via usb_descriptor.c. I haven't been able to find any documentation talking about this but experimentally it works as I describe