1. Event Context Information: Particle Data Run Information Platform, Run ID, TimeStamp Configuration Information Hardware and software configuration keys Datagram information Bookkeeping of datagrams, mode and status data “Extended Context Counters” (aka Scalars) Livetime, elapsed time, event number Numbers of prescaled, discarded and deadzone events TimeTone information GPS, 1-PPS information Status of GPS, 1-PPS information Allows to calibrate fluctuations in system clock Event time In system clock times

2. Digitization of the Context Probably have to store all these data for every event. About 156 bytes / event uncompressed Different applications might access only some of these fields Probably want to keep the on different ROOT branches

3. Event Ordering Issues Events from two streams are interleaved. Ordering is preserved within a single stream. To digitize events in order requires having both streams open at the same time, scanning context record for timing information 01_EPU0 00_EPU1 04_EPU0 03_EPU1 Time

4. Timing Issues Various Pieces of Timing Data Previous and Current TimeTones in Science stream Includes GPS seconds since epoch start TimeHack: 20 MHz and 1-PPS counters Includes GPS, 1-PPS validity flags 20MHz and 1-PPS counters at most recent time hack, sampled at event capture time Hopefully same as values at “Current” TimeTone 20MHz clock sampled at event capture time Total elapsed and deadtime since run start Data needed to extract local time GPS seconds at most recent valid TimeHack 20MHz clock calibrated rate Number 20MHz ticks since most recent valid tick hack