Synthese failed on DSP-Builder "Out of Memory 4200MB"

just like an accumulator looks. :)

a 2 input adder which feeds into a delay block. the first input of the adder is the same as your demux, and the 2nd comes from the output of the delay block. you can turn on the sclr function in your delay block to clear the accumulator every time you start a cycle. the sclr will be connected to one of the counters (or counter into a comparator) of your design. so clear whenever counter = 0 or 255 or whatever.