## Software

The whole correlator is controlled from the host computer by a program named “correl”, which communicates with all 8 units every second.

Every second, correl sends to all connected units the desired observing mode, the rate and phases for the LO3, the delays, etc..., and retrieves Continuum data from the previous second. This is done by scanning sequentially the connected units.

Every second, the units perform the FFT of the lag data, apply the “IF Pass Band” correction, correct the phases for small delay offsets, and compute the Continuum data by averaging over a frequency band specified by correl.

At the end of an observation, correl instruct a second program, correl_spectra to read sequentially all connected units to recover the Line data, cross or auto-correlation spectra on all baselines or all antennas.

After some reordering, correl transmits the data (Continuum and Line) to “RDI_PROGRAM” which computes and applies atmospheric calibration before writing it on disk.