PLP implements the Psion Link Protocol. 

This program is used to transfer data between a Psion Series 5mx
(default) or Psion Series 5 to a Unix server.  The ncp daemon is
started to communicate with the Psion and an ftp like interface is
provided by rfsv.

Before using this port it is necessary to either

    a) create a symbolic link form the serial port the psion is
    connected to /dev/psion eg ln -s /dev/cuaa0 /dev/psion

or

    b) start the ncp daemon with the correct serial port eg 
    ncp -s 7501 -d /dev/cuaa0 -s5