The D0 level 3 trigger/data acquisition and its real time control

Summary form only given. The D0 experiment at the Fermilab Tevatron will use an upgraded data acquisition system to handle the higher trigger rates planned for the Collider Run 2. Individual blocks from VME digitizing crates flow to multiport memories associated with Level 3 farm nodes, which are generic Intel systems running Windows NT. New modules have been designed to enable the blocks to move independently in a data driven mode, using Fibre Channel, to individual segments of the Level 3 processor farm operated in parallel. These modules incorporate logic that allows complex routing of the data blocks, driven by the trigger bits associated with the event. This routing permits trigger-specific event assignment to one of a given group of filter nodes or to multiple nodes, as well as the shadowing by a filter test node(s) of specific trigger processing. The design meets the initial Run 2 requirement to readout 250 Kbyte events at over 1 KHz, and is upgradeable by stages to an order of magnitude higher rate. The system must be able to change configuration quickly from regular data taking to calibration, cosmic ray, or special diagnostic triggering. The control system is based on several technologies from the standard networking tools and custom control systems and resource allocators/planners. The system is written in C++ and uses a number of tools publicly available like ACE. The entire Level 3 system is based on Windows NT Basic versions of the D0 data acquisition are running at D0 and at a separate electronics test site at Fermilab as well as at Brown, where prototype modules are tested and control software is written.