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 
*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.