The first stage of SLT processing is segment finding. The data arrives at level one of the SLT (level zero being at the DSP's and ROC's) one crate's worth per global first level trigger (GFLT) accept. Pattern recognition is performed in the local non-orthogonal (LNO) coordinate system of a single cell [1, 6] and hits not placed on segments are ignored. A list of wire numbers and drifts for each found segment are passed on to the next level of processing one cell at a time.
For some GSLT accepts (set by the monitoring frequency) the cells of segment hits are also concatenated together into a crate data structure for monitoring. When a segment finding transputer has processed all the FADC hits in its crate an end-of-data packet is sent to level two and the monitoring data is passed to a global CTD readout transputer. The global CTD readout transputer is responsible for concatenating the 16 crates of segment hit data together, adding an ADAMO header, and passing this data to the EVB. The monitoring data is also used to fill the online histograms.
Since the segment finding transputers form the top of the SLT harness tree they are responsible, via the node server process, for routing messages between levels zero and two, and levels zero and three. Hence FADC hit data, z-data, and monitoring data will be transmitted on the link between the FADC-ROC and the segment finding transputers. Control signals are also transmitted along this link and are propagated up the SLT network along the trigger data path.
All operations running on the segment finding transputer are performed in integer arithmetic.