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I have a question about generating square waves with finite length by using a Raspberry Pi Pico. For example, I want to generate a 20 kHz square wave with 100 periods, or to generate a 20 kHz square wave with an exact 1 ms. I cannot have accurate control over it.

To generate an infinite length of square waves is easy, as there are lots of examples online. I can use PIO to achieve it. For example, the following code could do so:

import rp2
from machine import Pin 
@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
def blink():
    set(pins, 1)
    set(pins, 0)

sm = rp2.StateMachine(0, blink, freq=25000, set_base=Pin(26))

sm.active(1)

However, I don't know how to accurately control the length/periods of the square wave. By using time.sleep() is not accurate at all.

Thank you in advance!

Chang
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1 Answers1

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Use the "decrement X" instruction in the PIO to count the number of cycles you want. Might have to add some delays to get back a square wave. jmp(x_dec, "top_of_loop"). You'd hang, waiting for some input, and read the X value from the input FIFO. Then you'd run the square-wave loop, decrementing X. When it hits zero, you jump to the outer loop, where you again wait for a new X value for the number of cycles. I think that's it!

aMike
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