Raspberry Pi Pico - Generate finite length square wave

Question

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!

aMike · Accepted Answer · 2021-08-20 02:16:50Z

2

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!

answered Aug 20, 2021 at 2:16

aMike

9476 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Chang Over a year ago

Thank you! I got it.

Collectives™ on Stack Overflow

Raspberry Pi Pico - Generate finite length square wave

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related