Square Wave Generator

A square wave is a periodic waveform that alternates between two discrete values.

Here's an example square wave that is generated using a simple Python function.



In [1]:

    
import matplotlib.pyplot as plt
import numpy as np
%matplotlib inline

x = np.arange(0, 100)

def square(x):
    return (x % 50) < 25

plt.plot(x, square(x))









    Out[1]:





[<matplotlib.lines.Line2D at 0x1188c82e8>]



In [2]:

    
import magma as m
m.set_mantle_target("ice40")

To implement our square wave in magma, we start by importing the IceStick module from loam. We instance the IceStick and turn on the Clock and J3[0] (configured as an output).

Now we'll use magma and mantle to implement a square wave generator. Since our square wave just toggles between 0 and 1 using a fixed period, we can use any bit in a synchronous counter to implement it (choosing a certain counter bit will change the period).



In [3]:

    
import mantle
from loam.boards.icestick import IceStick

icestick = IceStick()
icestick.Clock.on()
icestick.J3[0].output().on()

main = icestick.main()

counter = mantle.Counter(32)
square = counter.O[9]

m.wire( square, main.J3 )









    



import lattice ice40
import lattice mantle40

Compile and build the circuit.



In [4]:

    
m.compile('build/square', main)



In [5]:

    
%%bash
cd build
cat square.pcf
yosys -q -p 'synth_ice40 -top main -blif square.blif' square.v
arachne-pnr -q -d 1k -o square.txt -p square.pcf square.blif 
icepack square.txt square.bin
iceprog square.bin









    



set_io J3 62
set_io CLKIN 21






    



init..
cdone: high
reset..
cdone: low
flash ID: 0x20 0xBA 0x16 0x10 0x00 0x00 0x23 0x64 0x34 0x65 0x03 0x00 0x71 0x00 0x26 0x27 0x12 0x16 0xD3 0xE4
file size: 32220
erase 64kB sector at 0x000000..
programming..
reading..
VERIFY OK
cdone: high
Bye.

We can wire up GPIO pin 62 to a logic analyzer to verify that our circuit produces the correct square waveform.