77 lines
1.9 KiB
Python
77 lines
1.9 KiB
Python
# Copyright (C) 2012 Vermeer Manufacturing Co.
|
|
# License: GPLv3 with additional permissions (see README).
|
|
|
|
from math import cos, pi
|
|
from scipy import signal
|
|
import matplotlib.pyplot as plt
|
|
|
|
from migen.fhdl.std import *
|
|
from migen.fhdl import verilog
|
|
from migen.genlib.misc import optree
|
|
from migen.sim.generic import Simulator
|
|
|
|
# A synthesizable FIR filter.
|
|
class FIR(Module):
|
|
def __init__(self, coef, wsize=16):
|
|
self.coef = coef
|
|
self.wsize = wsize
|
|
self.i = Signal((self.wsize, True))
|
|
self.o = Signal((self.wsize, True))
|
|
|
|
###
|
|
|
|
muls = []
|
|
src = self.i
|
|
for c in self.coef:
|
|
sreg = Signal((self.wsize, True))
|
|
self.sync += sreg.eq(src)
|
|
src = sreg
|
|
c_fp = int(c*2**(self.wsize - 1))
|
|
muls.append(c_fp*sreg)
|
|
sum_full = Signal((2*self.wsize-1, True))
|
|
self.sync += sum_full.eq(optree("+", muls))
|
|
self.comb += self.o.eq(sum_full[self.wsize-1:])
|
|
|
|
# A test bench for our FIR filter.
|
|
# Generates a sine wave at the input and records the output.
|
|
class TB(Module):
|
|
def __init__(self, coef, frequency):
|
|
self.submodules.fir = FIR(coef)
|
|
self.frequency = frequency
|
|
self.inputs = []
|
|
self.outputs = []
|
|
|
|
def do_simulation(self, s):
|
|
f = 2**(self.fir.wsize - 1)
|
|
v = 0.1*cos(2*pi*self.frequency*s.cycle_counter)
|
|
s.wr(self.fir.i, int(f*v))
|
|
self.inputs.append(v)
|
|
self.outputs.append(s.rd(self.fir.o)/f)
|
|
|
|
def main():
|
|
# Compute filter coefficients with SciPy.
|
|
coef = signal.remez(30, [0, 0.1, 0.2, 0.4, 0.45, 0.5], [0, 1, 0])
|
|
|
|
# Simulate for different frequencies and concatenate
|
|
# the results.
|
|
in_signals = []
|
|
out_signals = []
|
|
for frequency in [0.05, 0.1, 0.25]:
|
|
tb = TB(coef, frequency)
|
|
sim = Simulator(tb)
|
|
sim.run(200)
|
|
del sim
|
|
in_signals += tb.inputs
|
|
out_signals += tb.outputs
|
|
|
|
# Plot data from the input and output waveforms.
|
|
plt.plot(in_signals)
|
|
plt.plot(out_signals)
|
|
plt.show()
|
|
|
|
# Print the Verilog source for the filter.
|
|
fir = FIR(coef)
|
|
print(verilog.convert(fir, ios={fir.i, fir.o}))
|
|
|
|
main()
|