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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN"[]>
<book>
<bookinfo>
<title>libraw1394</title>
<subtitle>version 0.9</subtitle>
<copyright>
<year>2001</year>
<holder>Andreas Bombe</holder>
</copyright>
</bookinfo>
<toc></toc>
<chapter id="introduction">
<title>Introduction</title>
<para>
The Linux kernel's IEEE 1394 subsystem provides access to the raw 1394 bus
through the raw1394 module. This includes the standard 1394 transactions
(read, write, lock) on the active side, isochronous stream receiving and
sending and dumps of data written to the FCP_COMMAND and FCP_RESPONSE
registers. raw1394 uses a character device to communicate to user
programs using a special protocol.
</para>
<para>
libraw1394 was created with the intent to hide that protocol from
applications so that
<orderedlist numeration="arabic">
<listitem>
<para>
the protocol has to be implemented correctly only once.
</para>
</listitem>
<listitem>
<para>
all work can be done using easy to understand functions instead of
handling a complicated command structure.
</para>
</listitem>
<listitem>
<para>
only libraw1394 has to be changed when raw1394's interface changes.
</para>
</listitem>
</orderedlist>
</para>
<para>
To fully achieve the goals (especially 3) libraw1394 is distributed under
the LGPL (Lesser General Public License - see file COPYING.LIB for more
information.) to allow linking with any program, be it open source or
binary only. The requirements are that the libraw1394 part can be
replaced (relinked) with another version of the library and that changes
to libraw1394 itself fall under LGPL again. Refer to the LGPL text for
details.
</para>
</chapter>
<chapter id="intro1394">
<title>Short Introduction into IEEE 1394</title>
<para>
IEEE 1394 in fact defines two types of hardware implementations for this
bus system, cable and backplane. The only one described here and
supported by the Linux subsystem is the cable implementation. Most people
not familiar with the standard probably don't even know that there is
something else than the 1394 cable specification.
</para>
<para>
If you are familiar with CSR architectures (as defined in IEEE 1212
(FIXME?)), then you already know most of 1394, which is a CSR
implementation.
</para>
<sect1>
<title>Bus Structure</title>
<para>
The basic data structures defined in the standard and used in this
document are the quadlet (32 bit quantity) and the octlet (64 bit
quantity) and blocks (any quantity of bytes). The bus byte ordering is
big endian. A transmission can be sent at one of multiple possible
speeds, which are 100, 200 and 400 Mbit/s for the currently mostly used
IEEE 1394a spec and up to 3.2 Gbit/s in the recently finalized 1394.b
standard (these speeds are also referred to as S100, S200, ...).
</para>
<para>
A 1394 bus consists of up to 64 nodes (with multiple buses possibly
being connected, but that is outside of the scope of this document and
not completely standardized yet), each having a local address space with
48 bit wide addressing. Each node is addressed with a 16 bit address,
which is further divided into a 10 bit bus ID and a 6 bit local node ID.
The highest value for both is a special value. Bus ID equal to 1023
means "local bus" (the bus the node is connected to), node ID equal to
63 means "all nodes" (broadcast).
</para>
<para>
The whole bus can thus be seen as a linear 64 bit address space by
concatenating the node address (most significant bits) and and node
address (least significant bits). libraw1394 treats them separately in
function arguments to save the application some fiddling with the bits.
The node IDs are completely dynamic and determined during the bus reset.
</para>
<para>
Unlike other buses there aren't many transactions or commands defined,
higher level commands are defined in terms of addresses accessed instead
of separate transaction types (comparable to memory mapped registers in
hardware). The 1394 transactions are:
<itemizedlist>
<listitem>
<para>read (quadlets and blocks)</para>
</listitem>
<listitem>
<para>write (quadlets and blocks)</para>
</listitem>
<listitem>
<para>lock (some atomic modifications)</para>
</listitem>
</itemizedlist>
There is also the isochronous transaction (the above three are called
asynchronous transactions), which is a broadcast stream with guaranteed
bandwidth. It doesn't contain any address but is distinguished by a 6
bit channel number.
</para>
<para>
The bus view is only logical, physically it consists of many
point-to-point connections between nodes with every node forwarding data
it receives to every other port which is capable of the speed the
transaction is sent at (thus a S200 node in the path between two S400
nodes would limit their communication speed to S200). It forms a tree
structure with all but one node having a parent and a number of
children. One node is the root node and has no parents.
</para>
</sect1>
<sect1>
<title>Bus Reset</title>
<para>
A bus reset occurs whenever the state of any node changes (including
addition and removal of nodes). At the beginning a root node is chosen,
then the tree identification determines for every node which port is
connected to a parent, child or nothing. Then the SelfID phase begins.
The root node sends a SelfID grant on its first port connected to a
child. If that is not a leaf node, it will itself forward the grant to
its first child. When a leaf node gets a grant, it will pick the lowest
node ID not yet in use (starting with 0) and send out a SelfID packet
with its node ID and more information, then acknowledge the SelfID grant
to its parent, which will send a grant to its next child until it
configured all its children, then pick a node ID itself, send SelfID
packet and ack to parent.
</para>
<para>
After bus reset the used node IDs are in a sequential range with no
holes starting from 0 with the root node having the highest ID. This
also means that node IDs can change for many or all nodes with the
insertion of a new node or moving the role of root to another node. In
libraw1394 all transactions are tagged automatically with a generation
number which is increased in every bus reset and transactions with an
obsolete generation will fail in order to avoid targetting the wrong
node. Nodes have to be identified in a different way than their
volatile node IDs, namely by reading their globally unique ID (GUID)
contained in the configuration ROM.
</para>
</sect1>
<sect1>
<title>Transactions</title>
<para>
The packets transmitted on the bus are acknowledged by the receiving end
unless they are broadcast packets (broadcast writes and isochronous
packets). The acknowledge code contains an error code, which either
signifies error, success or packet pending. In the first two cases the
transaction completes, in the last a response packet will follow at a
later time from the targetted node to the source node (this is called a
split transaction). Only writes can succeed and complete in the ack
code, reads and locks require a response. Error and packet pending can
happen for every transaction. The response packets contain a response
code (rcode) which signifies success or type of error.
</para>
<para>
For read and write there are two different types, quadlet and block.
The quadlet types have all their payload (exactly one quadlet) in the
packet header, the block types have a variable length data block
appended to the header. Programs using libraw1394 don't have to care
about that, quadlet transactions are automatically used when the data
length is 4 bytes and block transactions otherwise.
</para>
<para>
The lock transaction has several extended transaction codes defined
which choose the atomic operation to perform, the most used being the
compare-and-swap (code 0x2). The transaction passes the data value and
(depending on the operation) the arg value to the target node and
returns the old value at the target address, but only when the
transaction does not have an error. All three values are of the same
size, either one quadlet or one octlet.
</para>
<para>
In the compare-and-swap case, the data value is written to the target
address if the old value is identical to the arg value. The old value
is returned in any case and can be used to find out whether the swap
succeeded by repeating the compare locally. Compare-and-swap
is useful for avoiding race conditions when accessing the same
address from multiple nodes. For example, isochronous resource
allocation is done using compare-and-swap, as described below. Since
the old value is always returned, it more efficient to do the first
attempt with the reset value of the target register as arg instead of
reading it first. Repeat with the returned old value as new arg value
if it didn't succeed.
</para>
</sect1>
<sect1>
<title>Bus Management</title>
<para>
There are three basic bus service nodes defined in IEEE 1394 (higher
level protocols may define more): cycle master, isochronous resource
manager and bus manager. These positions are contended for in and
shortly after the bus reset and may all be taken by a single node. A
node does not have to support being any of those but if it is bus
manager capable it also has to be iso manager capable, if it is iso
manager capable it also has to be cycle master capable.
</para>
<para>
The cycle master sends 8000 cycle start packets per second, which
initiate an iso cycle. Without that, no isochronous transmission is
possible. Only the root node is allowed to be cycle master, if it is
not capable then no iso transmissions can occur (and the iso or bus
manager have to select another node to become root and initiate a bus
reset).
</para>
<para>
The isochronous resource manager is the central point where channel and
bandwidth allocations are stored. A bit in the SelfID shows whether a
node is iso manager capable or not, the iso manager capable node with
the highest ID wins the position after a bus reset. Apart from
containing allocation registers, this one doesn't do much. Only if
there is no bus manager, it may determine a cycle master capable node to
become root and initiate a bus reset.
</para>
<para>
The bus manager has more responsibilities: power management (calculate
power provision and consumption on the bus and turn on disabled nodes if
enough power is available), bus optimization (calculate an effective gap
count, optimize the topology by selecting a better positioned node for
root) and some registers relevant to topology (topology map containing
the SelfIDs of the last reset and a speed map, which is obsoleted in
IEEE 1394a). The bus manager capable nodes contend for the role by
doing a lock transaction on the bus manager ID register in the iso
manager, the first to successfully complete the transaction wins the
role.
</para>
</sect1>
<sect1>
<title>Isochronous Transmissions</title>
<para>
Nodes can allocate a channel and bandwidth for isochronous transmissions
at the iso manager to broadcast timing critical data (e.g. multimedia
streams) on the bus. However these transmissions are unreliable, there
is no guarantee that every packet reaches the intended recipients (the
software and hardware involved also take iso packets a bit more
lightly). After a cycle start packet, the isochronous cycle begins and
every node can transmit iso packets, however only one packet per channel
is allowed. As soon as a gap of a certain length appears (i.e. no node
sends anymore), the iso cycle ends and the rest of the time until the
next cycle start is reserved for asynchronous packets.
</para>
<para>
The channel register on the iso manager consists of 64 bits, each of
which signifies one channel. A channel can be allocated by any node by
doing a compare-swap lock request with the new bitmask. Likewise the
bandwidth can be allocated by doing a lock request with the new value.
The bandwidth register contains the remaining time available for every
iso cycle. Since you allocate time, the maximum data you are allowed to
put into an iso packet depends on the speed you will send at.
</para>
<para>
On every bus reset, the resource registers are resetted to their initial
values (all channels free, all bandwidth minus some amount set aside for
asynchronous communication available), this has to happen since the
isochronous manager may have moved to another node. Isochronous
transmissions may continue with the old allocations for a certain
(FIXME) amount of time. During that time, the nodes have to reallocate
their resources and no new allocations are allowed to occur. Only after
this period new allocations may be done, this avoids nodes losing their
allocations over a bus reset.
</para>
<para>
libraw1394 does not provide special functions for allocating iso
resources nor does it clean up after programs when they exit. Protocols
exist that require the first node to use some resources to allocate it
and then leave it for the last node using it to deallocate it. This may
be different nodes, so automatic behaviour would be very undesirable in
these cases.
</para>
</chapter>
<chapter id="general">
<title>Data Structures and Program Flow</title>
<sect1>
<title>Overview</title>
<para>
The 1394 subsystem in Linux is divided into the classical
three layers, like most other interface subsystems in Linux.
The in-kernel subsystem consists of the ieee1394 core, which
provides basic services like handling of the 1394 protocol
(converting the abstract transactions into packets and back),
collecting information about bus and nodes and providing some
services to the bus that are required to be available for
standards conformant nodes (e.g. CSR registers). Below that
are the hardware drivers, which handle converting packets and
bus events to and from hardware accesses on specific 1394
chipsets.
</para>
<para>
Above the core are the highlevel drivers, which use the services
provided by the core to implement protocols for certain devices and act
as drivers to these. raw1394 is one such driver, however it is not
specialized to handle one kind of device but is designed to accept
commands from user space to do any transaction wanted (as far as
possible from current core design). Using raw1394, normal applications
can access 1394 nodes on the bus and it is not neccessary to write
kernel code just for that.
</para>
<para>
raw1394 communicates to user space like most device drivers do, through
device files in /dev. It uses a defined protocol on that device, but
applications don't have to and should not care about that. All of this
is taken care of by libraw1394, which provides a set of functions that
convert to and from raw1394 protocol packets and are a lot easier to
handle than that underlying protocol.
</para>
</sect1>
<sect1>
<title>Handles</title>
<para>
The handle presented to the application for using libraw1394 is the
raw1394handle_t, an opaque data structure (which means you don't need to
know its internals). The handle (and with it a connection to the kernel
side of raw1394) is obtained using
<function>raw1394_new_handle()</function>. Insufficient permissions to
access the kernel driver will result in failure of this function, among
other possibilities of failure.
</para>
<para>
While initializing the handle, a certain order of function calls have to
be obeyed or undefined results will occur. This order reflects the
various states of initialization to be done:
</para>
<para>
<orderedlist>
<listitem>
<para><function>raw1394_new_handle()</function></para>
</listitem>
<listitem>
<para><function>raw1394_get_port_info()</function></para>
</listitem>
<listitem>
<para><function>raw1394_set_port()</function></para>
</listitem>
</orderedlist>
</para>
</sect1>
<sect1>
<title>Ports</title>
<para>
A computer may have multiple 1394 buses connected by having multiple
1394 chips. Each of these is called a port, and the handle has to be
connected to one port before it can be used for anything. Even if no
nodes are connected to the chip in question, it forms a complete bus
(with just one node, itself).
</para>
<para>
A list of available ports together with some information about it (name
of the hardware, number of connected nodes) is available via
<function>raw1394_get_port_info()</function>, which is to be called
right after getting a fresh handle. The user should be presented with a
choice of available ports if there is more than one. It may be good
practice to do that even if there is only one port, since that may
result from a normally configured port just not being available, making
it confusing to be dropped right into the application attached to a port
without a choice and notion of anything going wrong.
</para>
<para>
The choice of port is then reported using
<function>raw1394_set_port()</function>. If this function fails and
<symbol>errno</symbol> is set to <symbol>ESTALE</symbol>, then
something has changed about the ports (port was added or removed)
between getting the port info and trying to set a port. It is
required that the current port list is fetched (presenting the user
with the choice again) and setting the port is retried with the new
data.
</para>
<para>
After a successful <function>raw1394_set_port()</function>, the get and
set port functions must not be used anymore on this handle. Undefined
results occur if you do so. To make up for this, all the other
functions are allowed now.
</para>
</sect1>
<sect1>
<title>The Event Loop</title>
<para>
All commands in libraw1394 are asynchronous, with some
synchronous wrapper functions for some types of transactions.
This means that there are two streams of data, one going into
raw1394 and one coming out. With this design you can send out
multiple transactions without having to wait for the response
before you can continue (sending out other transactions, for
example). The responses and other events (like bus resets and
received isochronous packets) are queued, and you can get them
with <function>raw1394_loop_iterate()</function> or
<function>raw1394_loop_iterate_timeout()</function> (which
always returns after a user-specified timeout if no
raw1394 event has occurred).
</para>
<para>
This forms an event loop you may already know from similar systems like
GUI toolkits. <function>raw1394_loop_iterate()</function> gets one
message from the event queue in raw1394, processes it with the
configured callback functions and returns the value returned by the
callback (so you can signal to the main loop from your callback; the
standard callbacks all return 0). It normally blocks when there are no
events and always processes only one event. If you are only receiving
broadcast events like isochronous packets you thus have to set up a loop
continuously calling the iterate function to get your callbacks called.
</para>
<para>
Often it is necessary to have multiple event loops and combine
them, e.g. if your application uses a GUI toolkit which also
has its own event loop. In that case you can use
<function>raw1394_get_fd()</function> to get the file
descriptor used for this handle by libraw1394. The fd can be
used to for <function>select()</function> or
<function>poll()</function> calls together with the other
loop's fd. (Most toolkits, like GTK and Qt, have special APIs
for integrating file descriptors into their own event loops).
</para>
<para>
If using <function>poll()</function>, you must test for
<symbol>POLLIN</symbol> and <symbol>POLLPRI</symbol>
events. If using <function>select()</function>, you must test
for both read and exception activity.
</para>
<para> If any of these conditions trigger, you should then call
<function>raw1394_loop_iterate()</function> to pick up the
event. <function>raw1394_loop_iterate()</function> is
guaranteed not to block when called immediately after select()
or poll() indicates activity. After the first call you
continue the main event loop. If more events wait, the
<function>select()</function>/<function>poll()</function> will
immediately return again.
</para>
<para>
You can also use the fd to set the <symbol>O_NONBLOCK</symbol> flag with
<function>fcntl()</function>. After that, the iterate function will not
block anymore but fail with <symbol>errno</symbol> set to
<symbol>EAGAIN</symbol> if no events wait. These are the only legal
uses for the fd returned by <function>raw1394_get_fd()</function>.
</para>
<para>
There are some functions which provide a synchronous wrapper for
transactions, note that these will call
<function>raw1394_loop_iterate()</function> continuously until their
transaction is completed, thus having implicit callback invocations
during their execution. The standard transaction functions have names
of the form <function>raw1394_start_xxx</function>, the synchronous
wrappers are called <function>raw1394_xxx</function>.
</para>
</sect1>
<sect1>
<title>Handlers</title>
<para>
There are a number of handlers which can be set using the appropriate
function as described in the function reference and which libraw1394
will call during a <function>raw1394_loop_iterate()</function>. These
are:
<itemizedlist>
<listitem>
<para>tag handler (called for completed commands)</para>
</listitem>
<listitem>
<para>bus reset handler (called when a bus reset happens)</para>
</listitem>
<listitem>
<para>iso handler (called when an iso packet is received)
(deprecated by the new iso API)</para>
</listitem>
<listitem>
<para>fcp handler (called when a FCP command or response is
received)</para>
</listitem>
</itemizedlist>
The bus reset handler is always called, the tag handler for every
command that completes, the iso handler and fcp handler are only called
when the application chooses to receive these packets. Handlers return
an integer value which is passed on by
<function>raw1394_loop_iterate()</function> (only one handler is called
per invocation), <constant>0</constant> is returned without a handler in
place.
</para>
<para>
The tag handler case is a bit special since the default handler is
actually doing something. Every command that you start can be given an
unsigned long tag which is passed untouched to the tag handler when the
event loop sees a completed command. The default handler expects this
value to be a pointer to a <structname>raw1394_reqhandle</structname>
structure, which contains a data pointer and its own callback function
pointer. The callback gets the untouched data pointer and error code as
arguments. If you want to use tags that are not
<structname>raw1394_reqhandle</structname> pointers you have to set up
your own tag handler.
</para>
</sect1>
<sect1>
<title>Generation Numbers</title>
<para>
libraw1394 and the kernel code use generation numbers to identify the
current bus configuration and increment those on every configuration
change. The most important generation number is stored per connected
1394 bus and incremented on every bus reset. There is another number
managed by raw1394 which identifies global changes (like a complete port
being added or removed), which is used for the
<function>raw1394_set_port()</function> function to make sure you don't
use stale port numbers. This is done transparently to you.
</para>
<para>
The bus generation number is more relevant for your work. Since nodes
can change IDs with every bus reset, it is very likely that you don't
want to send a packet you constructed with the old ID before you noticed
the bus reset. This does not apply to isochronous transmissions, since
they are broadcast and do not depend on bus configuration. Therefore
every packet is automatically tagged with the expected generation
number, and it will fail to send if that does not match the number
managed in the kernel for the port in question.
</para>
<para>
You get the current generation number through the bus reset handler. If
you don't set a custom bus reset handler, the default handler will
update the generation number automatically. If you set your own
handler, you can update the generation number to be used through
<function>raw1394_update_generation()</function> directly in the handler
or later.
</para>
</sect1>
<sect1>
<title>Error and Success Codes</title>
<para>
libraw1394 returns the ack/rcode pair in most transaction cases. The
rcode is undefined in cases where the ack code is not equal to
<symbol>ack_pending</symbol>. This is stored in a type
<type>raw1394_errcode_t</type>, from which the ack and rcode parts can
be extracted using two macros.
</para>
<para>
With the function <function>raw1394_errcode_to_errno()</function> it is
possible to convert this to an errno number that conveys roughly the
same meaning. Many developers will find that easier to handle. This is
done automatically for the synchronous read/write/lock wrapper
functions, i.e. they return 0 for success and a negative value for
failure, in which case they also set the <symbol>errno</symbol> variable
to the appropriate code. The raw ack/rcode pair can then still be
retrieved using <function>raw1394_get_errcode()</function>.
</para>
</sect1>
</chapter>
<chapter id="isochronous">
<title>Isochronous Transmission and Reception</title>
<sect1>
<title>Overview</title>
<para>
Isochronous operations involve sending or receiving a constant
stream of packets at a fixed rate of 8KHz. Unlike raw1394's
asynchronous API, where you "push" packets to raw1394
functions at your leisure, the isochronous API is based around
a "pull" model. During isochronous transmission or reception,
raw1394 informs your application when a packet must be sent or
received. You must fulfill these requests in a timely manner
to avoid breaking the constant stream of isochronous packets.
</para>
<para>
A raw1394 handle may be associated with one isochronous
stream, either transmitting or receiving (but not both at the
same time). To transmit or receive more than one stream
simultaneously, you must create more than one raw1394 handle.
</para>
</sect1>
<sect1>
<title>Initialization</title>
<para>
When a raw1394 handle is first created, no isochronous
stream is assocated with it. To begin isochronous
operations, call either
<function>raw1394_iso_xmit_init()</function> (transmission) or
<function>raw1394_iso_recv_init()</function>
(reception). The parameters to these functions are as follows:
</para>
<para>
<symbol>handler</symbol> is your function for queueing
packets to be sent (transmission) or processing received
packets (reception).
</para>
<para>
<symbol>buf_packets</symbol> is the number of packets that
will be buffered at the kernel level. A larger packet buffer
will be more forgiving of IRQ and application latency,
however it will consume more kernel memory. For most
applications, it is sufficient to buffer 2000-16000 packets
(0.25 seconds to 2.0 seconds maximum latency).
</para>
<para>
<symbol>max_packet_size</symbol> is the size, in bytes, of
the largest isochronous packet you intend to handle. This
size does not include the isochronous header but it does
include the CIP header specified by many isochronous
protocols.
</para>
<para>
<symbol>channel</symbol> is the isochronous channel on which
you wish to receive or transmit. (currently there is no
facility for multi-channel transmission or reception).
</para>
<para>
<symbol>speed</symbol> is the isochronous speed at which you
wish to operate. Possible values are
<symbol>RAW1394_ISO_SPEED_100</symbol> through
<symbol>RAW1394_ISO_SPEED_400</symbol>.
</para>
<para>
<symbol>irq_interval</symbol> is the maximum latency of the
kernel buffer, in packets. (To avoid excessive IRQ rates, the
low-level drivers only trigger an interrupt every
irq_interval packets). Pass -1 to receive a default value
that should be suitable for most applications.
</para>
<para>
If <function>raw1394_iso_xmit/recv_init()</function> retuns
successfully, then you may start isochronous operations. You
may not call
<function>raw1394_iso_xmit/recv_init()</function> again on
the same handle without first shutting down the isochronous
operation with <function>raw1394_iso_shutdown()</function>.
</para>
<para>
Note that <function>raw1394_iso_xmit_init()</function> and
<function>raw1394_iso_recv_init()</function> involve
potentially time-consuming operations like allocating kernel
and device resources. If you intend to transmit or receive
several isochronous streams simultaneously, it is advisable
to initialize all streams before starting any packet
transmission or reception.
</para>
</sect1>
<sect1>
<title>Stopping and Starting</title>
<para>
Once the isochronous operation has been initialized, you may
start and stop packet transmission with
<function>raw1394_iso_xmit/recv_start()</function> and
<function>raw1394_iso_stop()</function>. It is legal to call
these as many times as you want, and it is permissible to
start an already-started stream or stop an already-stopped
stream. Packets that have been queued for transmission or
reception will remain queued when the operation is stopped.
</para>
<para>
<function>raw1394_iso_xmit/recv_start()</function> allow you
to specify on which isochronous cycle number to start
transmitting or receiving packets. Pass -1 to start
immediately. This parameter is ignored if isochronous
transmission or reception is already in progress.
</para>
<para>
<function>raw1394_iso_xmit_start()</function> has an
additional parameter, <symbol>prebuffer_packets</symbol>,
which specifies how many packets to queue up before starting
transmission. Possible values range from zero (start
transmission immediately after the first packet is queued)
up to the total number of packets in the buffer.
</para>
<para>
Once the isochronous operation has started, you must
repeatedly call <function>raw1394_loop_iterate()</function>
as usual to drive packet processing.
</para>
</sect1>
<sect1>
<title>Receiving Packets</title>
<para>
Raw1394 maintains a fixed-size ringbuffer of packets in
kernel memory. The buffer is filled by the low-level driver
as it receives packets from the bus. It is your
application's job to process each packet, after which the
buffer space it occupied can be re-used for future packets.
</para>
<para>
The isochronous receive handler you provided will be called
from <function>raw1394_loop_iterate()</function> after each
packet is received. Your handler is passed a pointer to the
first byte of the packet's data payload, plus the packet's
length in bytes (not counting the isochronous header), the
cycle number at which it was received, the channel on which
it was received, and the "tag" and "sy" fields from the
isochronous header. Note that the packet is at this point
still in the kernel's receive buffer, so the data pointer is
only valid until the receive handler returns. You must make
a copy of the packet's data if you want to keep it.
</para>
<para>
The receive handler is also passed a "packet(s) dropped"
flag. If this flag is nonzero, it means that one or more
incoming packets have been dropped since the last call to
your handler (usually this is because the kernel buffer has
completely filled up with packets or a bus reset has
occurred).
</para>
</sect1>
<sect1>
<title>Transmitting Packets</title>
<para>
Similar to reception, raw1394 maintains a fixed-size
ringbuffer of packets in kernel memory. The buffer is filled
by your application as it queues packets to be sent. The
buffer is drained by the hardware driver as it transmits
packets on the 1394 bus.
</para>
<para>
The isochronous transmit handler you provided will be called
from <function>raw1394_loop_iterate()</function> whenever
there is space in the buffer to queue another packet. The
handler is passed a pointer to the first byte of the buffer
space for the packet's data payload, pointers to words
containing the data length in bytes (not counting the
isochronous header), "tag" and "sy" fields, and the
isochronous cycle number at which this packet will be
transmitted. The handler must write the packet's data
payload into the supplied buffer space, and set the values
pointed to by "len", "tag", and "sy" to the appropriate
values. The handler is permitted to write any number of data
bytes, up and including to the value of
<symbol>max_packet_size</symbol> passed to
<function>raw1394_iso_xmit_init()</function>.
</para>
<para>
Note: If you passed -1 as the starting cycle to
<function>raw1394_iso_xmit_init()</function>, the cycle
number provided to your handler will be incorrect until after
one buffer's worth of packets have been transmitted.
</para>
<para>
The transmit handler is also passed a "packet(s) dropped"
flag. If this flag is nonzero, it means that one or more
outgoing packets have been dropped since the last call to
your handler (usually this is because the kernel buffer has
gone completely empty or a bus reset has occurred).
</para>
</sect1>
<sect1>
<title>Shutting down</title>
<para>
When the isochronous operation has finished, call
<function>raw1394_iso_shutdown()</function> to release all
associated resources. If you don't call this function
explicitly, it will be called automatically when the raw1394
handle is destroyed.
</para>
</sect1>
</chapter>
<chapter id="functions">
<title>Function Reference</title>
<refentry>
<refmeta>
<refentrytitle>raw1394_new_handle</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_new_handle</refname>
<refpurpose>create new handle</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>raw1394handle_t <function>raw1394_new_handle</function></funcdef>
<void>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
Creates and returns a new handle. It is not allowed to use the same
handle in multiple threads or forked processes. It is allowed to
create and use multiple handles, however. Use one handle per thread
which needs it in the multithreaded case.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
Returns the created handle or <constant>NULL</constant> when
initialization fails. In the latter case <varname>errno</varname>
either contains some OS specific error code or <constant>0</constant>
if the error is that libraw1394 and raw1394 don't support each other's
protocol versions.
</para>
</refsect1>
</refentry>
<refentry>
<refmeta>
<refentrytitle>raw1394_destroy_handle</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_destroy_handle</refname>
<refpurpose>deallocate handle</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>raw1394_destroy_handle</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>handle</parameter></term>
<listitem>
<para>handle to be deallocated</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>
Closes connection with raw1394 on this handle and deallocates
everything associated with it. It is safe to pass
<constant>NULL</constant> as handle, nothing is done in this case.
</para>
</refsect1>
</refentry>
<refentry>
<refmeta>
<refentrytitle>raw1394_get_port_info</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_get_port_info</refname>
<refpurpose>get information about connected ports</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>raw1394_get_port_info</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
<paramdef>struct raw1394_port_info *<parameter>pinf</parameter></paramdef>
<paramdef>int <parameter>maxports</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>pinf</parameter></term>
<listitem>
<para>Pointer to an array of structure of type
<structname>raw1394_port_info</structname> which will be filled in
by the function.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>maxports</parameter></term>
<listitem>
<para>Maximum number of <parameter>pinf</parameter> structures to
fill in. Zero is valid.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
The number of ports currently existing.
</para>
</refsect1>
<refsect1>
<title>Description</title>
<para>
Before you can set which port to use, you use this function to find
out which ports exist. The <structname>raw1394_port_info</structname>
structure looks like this:
<programlisting>
struct <structname>raw1394_portinfo</structname> {
int <structfield>nodes</structfield>;
char <structfield>name</structfield>[32];
};
</programlisting>
</para>
<para>
The field <structfield>nodes</structfield> contains the number of
nodes that are currently connected to that port, the field
<structfield>name</structfield> contains the name of the hardware
type. If your program is interactive, you should present the user
with this list to let them decide which port to use. A
non-interactive program (and probably interactive ones, too) should
provide a command line option to choose the port.
</para>
</refsect1>
</refentry>
<refentry>
<refmeta>
<refentrytitle>raw1394_get_fd</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_get_fd</refname>
<refpurpose>get the communication file descriptor</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>raw1394_get_fd</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>handle</parameter></term>
<listitem>
<para>handle of which the fd is to be returned from</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>
Returns the fd used for communication with the raw1394 kernel module.
This can be used for
<function>select()</function>/<function>poll()</function> calls if you
wait on other fds or can be integrated into another event loop
(e.g. from a GUI application framework). It can also be used to
set/remove the <constant>O_NONBLOCK</constant> flag using
<function>fcntl()</function> to modify the block behaviour in
<function>raw1394_loop_iterate()</function>. It must not be used for
anything else.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
The fd of the communication stream. Invalid fds may be returned
before a port was set using <function>raw1394_set_port()</function>.
</para>
</refsect1>
</refentry>
<refentry>
<refmeta>
<refentrytitle>raw1394_(get|set)_userdata</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_get_userdata</refname>
<refname>raw1394_set_userdata</refname>
<refpurpose>associate user data with a handle</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>void *<function>raw1394_get_userdata</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>raw1394_set_userdata</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>handle</parameter></term>
<listitem>
<para>handle associated with the user data</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>
Allows to associate one void pointer with a handle. libraw1394 does
not care about the data, it just stores it in the handle allowing it
to be retrieved at any time. This can be useful when multiple handles
are used, so that callbacks can identify the handle.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
<function>raw1394_get_userdata()</function> returns the void pointer
associated with the handle.
</para>
</refsect1>
</refentry>
<refentry>
<refmeta>
<refentrytitle>raw1394_get_(local_id|irm_id|nodecount)</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>raw1394_get_local_id</refname>
<refname>raw1394_get_irm_id</refname>
<refname>raw1394_get_nodecount</refname>
<refpurpose>return basic information about the bus</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>nodeid_t <function>raw1394_get_local_id</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>nodeid_t <function>raw1394_get_irm_id</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>raw1394_get_nodecount</function></funcdef>
<paramdef>raw1394handle_t <parameter>handle</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>handle</parameter></term>
<listitem>
<para>handle associated with a 1394 bus</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>
These functions return information about the 1394 bus the handle is
associated with. The values that can be queried through these
functions can change with every bus reset.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
<function>raw1394_get_local_id()</function> returns the node ID of the
local node (i.e. the hardware the driver is controlling directly).
<function>raw1394_get_irm_id()</function> returns the node ID of the
node that has become isochronous resource manager.
<function>raw1394_get_nodecount</function> returns the number of nodes
currently on the bus (including the local node).
</para>
</refsect1>
</refentry>
</chapter>
</book>