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+What: /dev/fw[0-9]+
+Date: May 2007
+KernelVersion: 2.6.22
+Contact: linux1394-devel@lists.sourceforge.net
+Description:
+ The character device files /dev/fw* are the interface between
+ firewire-core and IEEE 1394 device drivers implemented in
+ userspace. The ioctl(2)- and read(2)-based ABI is defined and
+ documented in <linux/firewire-cdev.h>.
+
+ This ABI offers most of the features which firewire-core also
+ exposes to kernelspace IEEE 1394 drivers.
+
+ Each /dev/fw* is associated with one IEEE 1394 node, which can
+ be remote or local nodes. Operations on a /dev/fw* file have
+ different scope:
+ - The 1394 node which is associated with the file:
+ - Asynchronous request transmission
+ - Get the Configuration ROM
+ - Query node ID
+ - Query maximum speed of the path between this node
+ and local node
+ - The 1394 bus (i.e. "card") to which the node is attached to:
+ - Isochronous stream transmission and reception
+ - Asynchronous stream transmission and reception
+ - Asynchronous broadcast request transmission
+ - PHY packet transmission and reception
+ - Allocate, reallocate, deallocate isochronous
+ resources (channels, bandwidth) at the bus's IRM
+ - Query node IDs of local node, root node, IRM, bus
+ manager
+ - Query cycle time
+ - Bus reset initiation, bus reset event reception
+ - All 1394 buses:
+ - Allocation of IEEE 1212 address ranges on the local
+ link layers, reception of inbound requests to such
+ an address range, asynchronous response transmission
+ to inbound requests
+ - Addition of descriptors or directories to the local
+ nodes' Configuration ROM
+
+ Due to the different scope of operations and in order to let
+ userland implement different access permission models, some
+ operations are restricted to /dev/fw* files that are associated
+ with a local node:
+ - Addition of descriptors or directories to the local
+ nodes' Configuration ROM
+ - PHY packet transmission and reception
+
+ A /dev/fw* file remains associated with one particular node
+ during its entire life time. Bus topology changes, and hence
+ node ID changes, are tracked by firewire-core. ABI users do not
+ need to be aware of topology.
+
+ The following file operations are supported:
+
+ open(2)
+ Currently the only useful flags are O_RDWR.
+
+ ioctl(2)
+ Initiate various actions. Some take immediate effect, others
+ are performed asynchronously while or after the ioctl returns.
+ See the inline documentation in <linux/firewire-cdev.h> for
+ descriptions of all ioctls.
+
+ poll(2), select(2), epoll_wait(2) etc.
+ Watch for events to become available to be read.
+
+ read(2)
+ Receive various events. There are solicited events like
+ outbound asynchronous transaction completion or isochronous
+ buffer completion, and unsolicited events such as bus resets,
+ request reception, or PHY packet reception. Always use a read
+ buffer which is large enough to receive the largest event that
+ could ever arrive. See <linux/firewire-cdev.h> for descriptions
+ of all event types and for which ioctls affect reception of
+ events.
+
+ mmap(2)
+ Allocate a DMA buffer for isochronous reception or transmission
+ and map it into the process address space. The arguments should
+ be used as follows: addr = NULL, length = the desired buffer
+ size, i.e. number of packets times size of largest packet,
+ prot = at least PROT_READ for reception and at least PROT_WRITE
+ for transmission, flags = MAP_SHARED, fd = the handle to the
+ /dev/fw*, offset = 0.
+
+ Isochronous reception works in packet-per-buffer fashion except
+ for multichannel reception which works in buffer-fill mode.
+
+ munmap(2)
+ Unmap the isochronous I/O buffer from the process address space.
+
+ close(2)
+ Besides stopping and freeing I/O contexts that were associated
+ with the file descriptor, back out any changes to the local
+ nodes' Configuration ROM. Deallocate isochronous channels and
+ bandwidth at the IRM that were marked for kernel-assisted
+ re- and deallocation.
+
+Users: libraw1394
+ libdc1394
+ tools like jujuutils, fwhack, ...