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STRUCT USB_HOST_CONF(9) | Host-Side Data Types and Macro | STRUCT USB_HOST_CONF(9) |
NAME¶
struct_usb_host_config - representation of a device's configurationSYNOPSIS¶
struct usb_host_config { struct usb_config_descriptor desc; char * string; struct usb_interface_assoc_descriptor * intf_assoc[USB_MAXIADS]; struct usb_interface * interface[USB_MAXINTERFACES]; struct usb_interface_cache * intf_cache[USB_MAXINTERFACES]; unsigned char * extra; int extralen; };
MEMBERS¶
descthe device's configuration descriptor.
string
pointer to the cached version of the
iConfiguration string, if present for this configuration.
intf_assoc[USB_MAXIADS]
list of any interface association descriptors
in this config
interface[USB_MAXINTERFACES]
array of pointers to usb_interface structures,
one for each interface in the configuration. The number of interfaces is
stored in desc.bNumInterfaces. These pointers are valid only while the the
configuration is active.
intf_cache[USB_MAXINTERFACES]
array of pointers to usb_interface_cache
structures, one for each interface in the configuration. These structures
exist for the entire life of the device.
extra
pointer to buffer containing all extra
descriptors associated with this configuration (those preceding the first
interface descriptor).
extralen
length of the extra descriptors buffer.
DESCRIPTION¶
USB devices may have multiple configurations, but only one can be active at any time. Each encapsulates a different operational environment; for example, a dual-speed device would have separate configurations for full-speed and high-speed operation. The number of configurations available is stored in the device descriptor as bNumConfigurations. A configuration can contain multiple interfaces. Each corresponds to a different function of the USB device, and all are available whenever the configuration is active. The USB standard says that interfaces are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot of devices get this wrong. In addition, the interface array is not guaranteed to be sorted in numerical order. Use usb_ifnum_to_if to look up an interface entry based on its number. Device drivers should not attempt to activate configurations. The choice of which configuration to install is a policy decision based on such considerations as available power, functionality provided, and the user's desires (expressed through userspace tools). However, drivers can call usb_reset_configuration to reinitialize the current configuration and all its interfaces.COPYRIGHT¶
March 2016 | Kernel Hackers Manual 3.2. |