SOURCENIC - Gets data from multicast source (i.e. rumeL box) from UDP port
            and sends data to file/pipe

<OUTPUT>    Output pipe  (header = header filled by m_initialize with SB data)
<ADDRESS>   Multicast address to receive data from (numerical in quotes)
<INTERFACE> IP address of interface to receive multicast data into
            (numerical in quotes)

Reads from the UDP port are blocking.  All data appearing at <PORT> will be
acquired, there is no check for which source it's coming from.

Socket buffer size is set internally to try to get /SBUFSZ, however,
for RHEL4U2 the max is set in the kernel to 256k. You can change the max value
to something more reasonable for high speed acquisition with the following
command:

/sbin/sysctl -w net.core.rmem_max=1048576

You can check to see what the current value is with the following command:
/sbin/sysctl net.core.rmem_max

(this sets it to 2MBytes). I have demonstrated the above value to be
adequate for gigabit ethernet acquisition WITHOUT anything else running on
the same CPU.

SWITCHES:
  /DEBUG      - debug info level
  /SDDSMODE=n - 1=raw_packets, 2=data_only, 3=header_only
  /FC=        - specify header format code as SB,SI,CB,CI (SB default)
  /XD=        - specify header abscissa increment (default 1.0)
  /PORT=n     - UDP port # to receive data (default = 29495, the SDDS port)
  /PRANGE=n   - range of ports to use starting at <PORT> (i.e. if
                 requested port is unavaliable)
  /TL=n       - # of bytes to transfer each pass. For SDDS data this
                 must be set to 1080 (the default)
  /SBUFSZ=n   - Desired socket buffer size in bytes.  Default=10M.
                 Kernel may or may not allow this size (see notes above)
  /NUMPKTS=   - Exit after output of specified number of SDDS packets


CONTROL WIDGETS:
  1. L:exit   - setting to any value other than 0 forces primitive to exit
  2. D:pktcnt - received packet counter

REVISION       PROGRAMMER      DESCRIPTION
--------       ----------      -------------------------------------
07-Feb-2007    dkc             baseline
27-Nov-2007    rdh             added output modes/switches/widgets

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