Using Linux PCs in DAQ applications

The ATLAS Data Acquisition/Event Filter prototype "-1" (DAQ/EF-1) project provides the opportunity to explore the use of commodity hardware (PCs) and Open Source Software (Linux) in DAQ applications. In DAQ/EF-1 there is an element called the LDAQ which is responsible for providing local run-control, error-handling and reporting for a number of Read-Out modules in Front End crates. This element is also responsible for providing event data for monitoring and for the interface with the global control and monitoring system (BackEnd). We present the results of an evaluation of the Linux operating system made in the context of DAQ/EF-I where there are no strong real-time requirements. We also report on our experience in implementing the LDAQ on a VMEbus based PC (the VMIVME-7587) and a desktop PC linked to VMEbus with a Bit3 interface both running Linux. We then present the problems encountered during the integration with VMEbus, the status of the LDAQ implementation and draw some conclusions on the use of Linux in DAQ applications.