code snippets for http://www.fpgarelated.com/showarticle/631.php

fpga631_snip1.py

@always_seq(clock.posedge, reset=reset)
def beh_sop():
    # tap update loop
    xd[0].next = x
    for ii in range(1, len(h)):
        xd[ii].next = xd[ii-1]
        
    # sum-of-products loop
    sop = 0
    for ii in range(len(h)):
        c = h[ii]
        sop = sop + (c * xd[ii])

    # scale the sum of products to the 
    # output range (truncate)
    y.next = sop >> scale

fpga631_snip2.py

def taps(x, N):
  return [x] if N <= 1 else [x] + taps(Reg(x), N-1)

w1 = sum([x*h for x, h in zip(taps(Reg(x), len(hs)), hs)])
w2 = w1 >> len(x)/2