Data Acquisition with a VAX 11/780 and MBD Branch Driver

In order to provide fast, convenient and flexible data acquisition, we have assembled a system using a CAMAC interface, a single general purpose data program for all channels in the MBD Branch Driver, and multiple VAX subprocesses to acquire, sort, and store data. Our use of the VAX subprocess capacity eliminates the need for a monitor program, allows easy reconfiguration of user software, and provides a simple means of having a modular general data acquisition software package. The subprocess structure is in keeping with our design goals of a modular system. The general purpose MBD program facilitates easy use by experimenters without a detailed knowledge of the MBD or CAMAC interface, while allowing them control of and access to the CAMAC hardware. The dual buffer system allows parallel sorting and data transfers. The use of the system service hybernation and time-demand priority provides for uninterrupted data flow while allowing offline users 50-90% of the CPU time. The use of DAP information files allows the user to change the hardware with relative ease. The system has been used for a number of initial experiments with a minimum amount of trouble. Our expectations of system performance, flexibility, and ease of programming change appear to be meet in these experiments.