A software approach for readout and data acquisition in CMS

Traditional systems dominated by performance constraints tend to neglect ot her qualities such a maintainability and configurability. Object-Orientatio n allows one to encapsulate the technology differences in communication sub -systems and to provide a uniform view of data transport layer to the syste ms engineer. We applied this paradigm to the design and implementation of i ntelligent data servers in the Compact Muon Solenoid (CMS) data acquisition system at CERN to easily exploiting the physical communication resources o f the available equipment. CMS is a high-energy physics experiment under st udy that incorporates a highly distributed data acquisition system. This pa per outlines the architecture of one part, the so called Readout Unit, and shows how we can exploit the object advantage for systems with specific dat a rate requirements. A C++ streams communication layer with zero copying fu nctionality has been established for UDP, TCP, DLPI and specific Myrinet an d VME bus communication on the VxWorks real-time operating system. This sof tware provides performance close to the hardware channel and hides communic ation details from the application programmers.