DEVICE(9)						   BSD Kernel Developer's Manual						 DEVICE(9)

NAME

     device -- an abstract representation of a device

SYNOPSIS

     typedef struct device *device_t;

DESCRIPTION

     The device object represents a piece of hardware attached to the system such as an expansion card, the bus which that card is plugged into,
     disk drives attached to the expansion card etc.  The system defines one device, root_bus and all other devices are created dynamically during
     autoconfiguration.  Normally devices representing top-level busses in the system (ISA, PCI etc.) will be attached directly to root_bus and
     other devices will be added as children of their relevant bus.

     The devices in a system form a tree.  All devices except root_bus have a parent (see device_get_parent(9)).  In addition, any device can have
     children attached to it (see device_add_child(9), device_add_child_ordered(9), device_find_child(9), device_get_children(9), and
     device_delete_child(9)).

     A device which has been successfully probed and attached to the system will also have a driver (see device_get_driver(9) and driver(9)) and a
     devclass (see device_get_devclass(9) and devclass(9)).  Various other attributes of the device include a unit number (see
     device_get_unit(9)), verbose description (normally supplied by the driver, see device_set_desc(9) and device_get_desc(9)), a set of bus-spe-
     cific variables (see device_get_ivars(9)) and a set of driver-specific variables (see device_get_softc(9)).

     Devices can be in one of several states:

     DS_NOTPRESENT  the device has not been probed for existence or the probe failed

     DS_ALIVE	    the device probe succeeded but not yet attached

     DS_ATTACHED    the device has been successfully attached

     DS_BUSY	    the device is currently open

     The current state of the device can be determined by calling device_get_state(9).

SEE ALSO

     devclass(9), driver(9)

AUTHORS

     This manual page was written by Doug Rabson.

BSD
								   June 16, 1998							       BSD