handling additional streaming-protocol signals in fir filters

The valid acts an enable to your filter. You ignore the first n valids until the filter is fully loaded, then you can just set output valid whenever the input is valid. If you are filtering a steam of data with no end, then this is fine, but if you need to do something special at the end of a set of data, you'll need extra logic to track of where you are in the data so you can take action at the appropriate time, and maybe flush the filter.