Modular software for MAST multi-technology data acquisition system

The MAST (Mega-Amp Spherical Tokamak) data acquisition system is being radically upgraded. New hardware with completely different control interface and logic has been installed on all system levels from front-end devices to plant control. MAST plant control has been moved from VMS to a Windows-based OPC system. Old CAMAC and VME units are being replaced by cPCI and PXI units. A number of CAMAC crates have been upgraded with new Ethernet controllers supporting useful front-end devices.The upgrade is being performed without disturbing operations; the data acquisition units are being replaced gradually. Such an upgrade is possible due to the structure of the MAST data acquisition system which is build as a set of autonomous units, each one controlled by a computer. Modern computers are capable of controlling several units, and this has been the major opportunity and challenge because it radically changes the unit control logic. As a result practically all system components had to be redesigned.The new unit software is a step in system evolution towards greater flexibility and universality. Each unit can now manage multiple data files, possibly with different formats, and many units can be hosted on the same computer. This feature is provided by a message proxy server. Each unit is controlled independently and transparently, exactly like a stand-alone unit. A message interface has been modified for consistent handling of new functions. The unit software supports event-triggered and real-time data acquisition at the system level. New software has been developed for a number of new hardware devices, and the device modules for all usable old devices have been rewritten to operate with the new control interface.The new software allows units to be upgraded even during operations. The system structure and logic provide easy extension. The system as a whole or system design elements could also be used on other fusion facilities.