Continuously live image processor for drift chamber track segment triggering

The first portion of the BABAR experiment Level 1 Drift Chamber Trigger pipeline is the Track Segment Finder (TSF). Using a novel method incorporating both occupancy and drift-time information, the TSF system continually searches for segments in the supercells of the full 7104-wire Drift Chamber hit image at 3.7 MHz. The TSF was constructed to operate in a potentially high beam-background environment while achieving high segment-finding efficiency, deadtime-free operation, a spatial resolution of <0.7 mm and a per-segment event time resolution of <70 ns. The TSF system consists of 24 hardware-identical TSF modules. These are the most complex modules in the BABAR trigger. On each module, fully parallel segment finding proceeds in 20 pipeline steps. Each module consists of a 9U algorithm board and a 6U interface board. The 9U printed circuit board has 10 layers and contains 0.9 million gates implemented in 25 FPGAs, which were synthesized from a total of 50,000 lines of VHDL. The boards were designed from the top-down with state-of-the-art CAD tools, which included gate-level board simulation. This methodology enabled production of a flawless board with no intermediate prototypes. It was fully tested with basic test patterns and 10⁵ simulated physics events