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