Abstract: The main-array ALMA correlator interfaces to the observatory by
means of a cluster of computers and dedicated interfaces. This computing
back-end configures the correlator to specific observing modes, receives
time domain correlation values and process them into raw visibilities with
an ALMA specific format. Results are delivered to other subsystems
(telescope calibration and archive) through a Data Distribution Service
(DDS) over Ethernet. All this is done in real-time while a higher level
control software schedules individual observations on different sub-arrays
at the same time. To achieve synchronization between sub-systems, a number
of hardware interfaces are implemented between antenna stations, the
correlator and the back-end cluster. The online software commands and
monitors the current status of the correlator, and it time synchronizes the
execution of specific actions through those interfaces. A fraction of the
instrumental delay in ALMA is adjusted in the correlator, and the same
interfaces are used to continuously command delay updates throughout the
observation. A time event synchronization signal is used to synchronize
with upstream digitizer devices that also apply instrumental delay
corrections to the signal path. This poster overviews the major
characteristics and functionality of those interfaces. The aim is to
showcase how is that ALMA computing has access to the correlator hardware,
and the software components used for a coordinated operation. In
preparation for eventual future improvements and changes to the interfaces,
or the introduction of a completely different correlator.