AccessRunner ADSL-USB Modem Device Set Data Sheet
4.1.2 Configuration Descriptor
A configuration descriptor describes information about a specific device configuration (see Table 4-2). The descriptor
describes the number of interfaces provided by the configuration.
Table 4-2. Configuration Descriptors
Size of this descriptor in bytes.
Total length of data returned for this configuration. Includes the
combined length of all descriptors (configuration, interface,
endpoint, and class or vendor specific) returned for this
Number of interfaces supported by this configuration.
Value to use as an argument to Set Configuration to select this
Index of string descriptor describing this configuration.
Reserved (reset to 0)
A device configuration that uses power from the bus and a local
source sets both D7 and D6. The actual power source at runtime
may be determined using the Get Status device request.
If a device configuration supports remote wakeup, D5 is set to 1.
Maximum power consumption of USB device from the bus in this
specific configuration when the device is fully operational.
Expressed in 2 mA units (i.e., 50 = 100 mA).
Note: A device configuration reports whether the configuration is
bus-powered or self-powered. Device status reports whether the
device is currently self-powered. If a device is disconnected from
its external power source, it updates device status to indicate that
it is no longer self-powered.
A device may not increase its power draw from the bus, when it
loses its external power source, beyond the amount reported by its
If a device can continue to operate when disconnected from its
external power source, it continues to do so. If the device cannot
continue to operate, it fails operations it can no longer support.
Host software may determine the cause of the failure by checking
the status and noting the loss of the device’s power source.