Function get_max_iso_packet_size

src/usb_control.cpp:133–179

  }

  int get_max_iso_packet_size(libusb_device *device, int configuration, int alternate_setting, int endpoint)
  {
    libusb_config_descriptor *config_desc;
    int r = LIBUSB_ERROR_NOT_FOUND;

    r = libusb_get_config_descriptor_by_value(device, configuration, &config_desc);

    if(r == LIBUSB_SUCCESS)
    {
      for(int interface_idx = 0; interface_idx < config_desc->bNumInterfaces; ++interface_idx)
      {
        const libusb_interface &interface = config_desc->interface[interface_idx];

        if(interface.num_altsetting > alternate_setting)
        {
          const libusb_interface_descriptor &interface_desc = interface.altsetting[alternate_setting];
          const libusb_endpoint_descriptor *endpoint_desc = 0;

          for(int endpoint_idx = 0; endpoint_idx < interface_desc.bNumEndpoints; ++endpoint_idx)
          {
            if(interface_desc.endpoint[endpoint_idx].bEndpointAddress == endpoint && (interface_desc.endpoint[endpoint_idx].bmAttributes & 0x3) == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS)
            {
              endpoint_desc = interface_desc.endpoint + endpoint_idx;
              break;
            }
          }

          if(endpoint_desc != 0)
          {
            libusb_ss_endpoint_companion_descriptor *companion_desc;
            // ctx is only used for error reporting, libusb should better ask for a libusb_device anyway...
            r = libusb_get_ss_endpoint_companion_descriptor(NULL /* ctx */, endpoint_desc, &companion_desc);

            if(r != LIBUSB_SUCCESS) continue;

            r = companion_desc->wBytesPerInterval;

            libusb_free_ss_endpoint_companion_descriptor(companion_desc);
            break;
          }
        }
      }
    }
    libusb_free_config_descriptor(config_desc);

    return r;
  }
}

UsbControl::UsbControl(libusb_device_handle *handle) :