Look into using messages between BoardReaders as a way to trigger readout
In thinking about how to synchronize the readout of slow controls data (so that it can be added to the primary data stream), Ron suggested a model in which one of the BoardReaders is designated as a source of readout messages and the BoardReaders that need to be told when to read out can listen for such messages.
We should look into providing this functionality. Whether or not it is being used should be configurable, of course. MPI could be used for transmitting messages, or there could be a different protocol used.