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>4.2. Initialization</A
></H1
><P
>&#13;	  When a raw1394 handle is first created, no isochronous
	  stream is assocated with it. To begin isochronous
	  operations, call either
	  <CODE
CLASS="function"
>raw1394_iso_xmit_init()</CODE
> (transmission) or
	  <CODE
CLASS="function"
>raw1394_iso_recv_init()</CODE
>
	  (reception). The parameters to these functions are as follows:
        </P
><P
>&#13;	  <CODE
CLASS="symbol"
>handler</CODE
> is your function for queueing
	  packets to be sent (transmission) or processing received
	  packets (reception).
	</P
><P
>&#13;          <CODE
CLASS="symbol"
>buf_packets</CODE
> 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).
	</P
><P
>&#13;	  <CODE
CLASS="symbol"
>max_packet_size</CODE
> 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.
	</P
><P
>&#13;	  <CODE
CLASS="symbol"
>channel</CODE
> is the isochronous channel on which
	  you wish to receive or transmit. (currently there is no
	  facility for multi-channel transmission or reception).
       </P
><P
>&#13;         <CODE
CLASS="symbol"
>speed</CODE
> is the isochronous speed at which you
         wish to operate. Possible values are
         <CODE
CLASS="symbol"
>RAW1394_ISO_SPEED_100</CODE
>, 
		 <CODE
CLASS="symbol"
>RAW1394_ISO_SPEED_200</CODE
>, and
         <CODE
CLASS="symbol"
>RAW1394_ISO_SPEED_400</CODE
>.
       </P
><P
>&#13;         <CODE
CLASS="symbol"
>irq_interval</CODE
> 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.
       </P
><P
>&#13;         <CODE
CLASS="symbol"
>mode</CODE
> for <CODE
CLASS="function"
>raw1394_iso_recv_init()</CODE
>
         sets whether to use packet-per-buffer or buffer-fill receive mode.
		 Possible values are <CODE
CLASS="symbol"
>RAW1394_DMA_DEFAULT</CODE
> (bufferfill 
		 on ohci1394), <CODE
CLASS="symbol"
>RAW1394_DMA_BUFFERFILL</CODE
>, and 
		 <CODE
CLASS="symbol"
>RAW1394_DMA_PACKET_PER_BUFFER</CODE
>.
       </P
><P
>&#13;         If <CODE
CLASS="function"
>raw1394_iso_xmit/recv_init()</CODE
> retuns
         successfully, then you may start isochronous operations. You
         may not call
         <CODE
CLASS="function"
>raw1394_iso_xmit/recv_init()</CODE
> again on
         the same handle without first shutting down the isochronous
         operation with <CODE
CLASS="function"
>raw1394_iso_shutdown()</CODE
>.
       </P
><P
>&#13;         Note that <CODE
CLASS="function"
>raw1394_iso_xmit_init()</CODE
> and
	 <CODE
CLASS="function"
>raw1394_iso_recv_init()</CODE
> 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.
       </P
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libraw1394-doc 2.1.0-1ubuntu1 / usr / share / doc / libraw1394-doc / libraw1394 / x167.html
