When a raw1394 handle is first created, no isochronous
stream is assocated with it. To begin isochronous
operations, call either
raw1394_iso_xmit_init() (transmission) or
raw1394_iso_recv_init()
(reception). The parameters to these functions are as follows:
handler is your function for queueing
packets to be sent (transmission) or processing received
packets (reception).
buf_packets 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).
max_packet_size 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.
channel is the isochronous channel on which
you wish to receive or transmit. (currently there is no
facility for multi-channel transmission or reception).
speed is the isochronous speed at which you
wish to operate. Possible values are
RAW1394_ISO_SPEED_100,
RAW1394_ISO_SPEED_200, and
RAW1394_ISO_SPEED_400.
irq_interval 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.
mode for raw1394_iso_recv_init()
sets whether to use packet-per-buffer or buffer-fill receive mode.
Possible values are RAW1394_DMA_DEFAULT (bufferfill
on ohci1394), RAW1394_DMA_BUFFERFILL, and
RAW1394_DMA_PACKET_PER_BUFFER.
If raw1394_iso_xmit/recv_init() retuns
successfully, then you may start isochronous operations. You
may not call
raw1394_iso_xmit/recv_init() again on
the same handle without first shutting down the isochronous
operation with raw1394_iso_shutdown().
Note that raw1394_iso_xmit_init() and
raw1394_iso_recv_init() 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.