Can all Processors be Asynchronous?

Sadly, the answer is ``No''. Not all the SUs that are called processors follow the model of a process that modifies a data structure in some reversible way. For example:-

• Standard input and output are considered to be processors but they don't modify the data structure, they simply move it between memory and an external medium.

• A filter is a processor that determines if the data structure satisfies some criteria but does not modify it.

• A pruner removes unwanted banks before output so does modify the data structure, but far from adding value, it subtracts it!

• The Monte Carlo and the calibration produce the same outputs. The same is true for the uncalibration and the unpacker. Processors that produce the same outputs cannot interwork asynchronously; whichever is the downstream one permantly modifies the results of the upstream one.

So, in drawing up rules to allow processors to be used as independently as possible from one another, we have to recognise that not all can be asynchronous. Instead we have one set of rules which, if observed, qualifies the processor to be called a Standard Processor, and an additional set of rules govern the operation of any Asynchronous Processor. In SNOMAN, all processors will be Standard Processors, but not all will be Asynchronous Processors. Indeed currently, only the fitters are asynchronous. More work needs to be done in this area when we assemble an interactive version of SNOMAN.