Interface for accessing analog output of a daq-board via comedi. 
      - Author
 - Marco Hackenberg 
 
      - 
      Jan Benda 
 
      - Bug:
 NI DAQCard cmd.stop_arg += 2048 needs to tested 
      unipolar support is not really working
      
      - Options
 - usenipfistart: Use as start source NI PFI channel
 
      - Trigger to analog input
 - You need to route the analog input start signal to pfi channel 0: 
*Devices
        Device1:
            plugin : ComediNIPFI
            device : /dev/comedi0
            ident  : pfi-1
            channel: 0
            routing: AI_START1
        and tell the ComediAnalogOutput that it will be triggered by this signal: *Analog Output Devices
        Device1:
      
            device       : /dev/comedi0
            ident        : ao-1
            usenipfistart: 0
            delays       : 0ms
       
      - Calibration:
 - For hardware calibrated boards (like NI E-Series boards) do 
$ comedi_calibrate --
reset --calibrate -f /dev/comedi0
 
       
      For software calibrated boards (like NI M-Series boards) do 
$ comedi_soft_calibrate -f /dev/comedi0
      You may want to read the man page of comedi_calibrate.