The Programmable Event Loop

The basic processing unit in SNOMAN is an event. During execution, SNOMAN will loop over the required number of events, repeating its given task. This will often consist of a specific sequence of processor calls set by a command such as

$processor_list 'INP FTT ANL END'

Such a scheme is adequate if all events are of a common type and are to be treated in the same manner. In more complex situations, the data stream may consist of several event types which need to be separated out and processed differently, some examples being:

• Calibrations / Other interactions,
• Small events / Large events (eg $\geq$30 hits),
• Fit successes / Fit failures.

The problem is tackled by the introduction of a Programmable Event Loop (PEL) which provides a means of controlling flow during the event cycle, so that processing may follow one of several alternative paths. Decisions about processing are based on the results of tests performed on the data by the event filter. This chapter describes how to set up such filter tests, and how to go beyond a $processor_list command and program the event loop.