BX number in trailer off by one
The BX number encoded in the BX trailer appears to be one more than expected using the CMS convention (of first BX=1)
The scdaq software begins counting the BX number from 0 when unpacking the trailer, which we agree to be technically incorrect. However, most of the time the value agrees with the value in the muon data frame.
Comparing against the LHC filling scheme, for a given run, they list the first colliding BX as 197. Conversely, in our scouting output, we extract the BX as 198 from the trailers. We believe that the LHC begins counting from 0, implying that somehow(?) the scouting is recording the correct bunch crossing (if one starts counting at 1).
Edited by Thomas Owen James