litex/examples/sim/fir.py

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from math import cos, pi
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from scipy import signal
import matplotlib.pyplot as plt
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from migen.fhdl.std import *
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from migen.fhdl import verilog
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from migen.genlib.misc import optree
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from migen.sim.generic import run_simulation
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# A synthesizable FIR filter.
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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))
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###
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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:])
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# 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 = []
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def do_simulation(self, selfp):
f = 2**(self.fir.wsize - 1)
v = 0.1*cos(2*pi*self.frequency*selfp.simulator.cycle_counter)
selfp.fir.i = int(f*v)
self.inputs.append(v)
self.outputs.append(selfp.fir.o/f)
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if __name__ == "__main__":
# Compute filter coefficients with SciPy.
coef = signal.remez(30, [0, 0.1, 0.2, 0.4, 0.45, 0.5], [0, 1, 0])
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# 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)
run_simulation(tb, ncycles=200)
in_signals += tb.inputs
out_signals += tb.outputs
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# Plot data from the input and output waveforms.
plt.plot(in_signals)
plt.plot(out_signals)
plt.show()
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# Print the Verilog source for the filter.
fir = FIR(coef)
print(verilog.convert(fir, ios={fir.i, fir.o}))