Code snippet: PWM generated at a specified frequency

[blippy]

I'm exploring PWM with the Pico. The good news is that you can set both the duty cycle and frequency of PWM. Here's an example which sets a 60% duty cycle on a 440Hz frequency on GPIO0:

Code: Select all

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/clocks.h"
#include "hardware/pwm.h"


typedef uint16_t u16;
typedef uint32_t u32;


int main() 
{
	// set your desired inputs here
	const u32 f_pwm = 440; // frequency we want to generate
	const u16 duty = 60; // duty cycle, in percent

	gpio_set_function(0, GPIO_FUNC_PWM); // Tell GPIO 0 it is allocated to the PWM
	uint slice_num = pwm_gpio_to_slice_num(0); // get PWM slice for GPIO 0 (it's slice 0)


	// set frequency
	// determine top given Hz - assumes free-running counter rather than phase-correct
	u32 f_sys = clock_get_hz(clk_sys); // typically 125'000'000 Hz
	float divider = f_sys / 1'000'000UL;  // let's arbitrarily choose to run pwm clock at 1MHz
	pwm_set_clkdiv(slice_num, divider); // pwm clock should now be running at 1MHz
	u32 top =  1'000'000UL/f_pwm -1; // TOP is u16 has a max of 65535, being 65536 cycles
	pwm_set_wrap(slice_num, top);

	// set duty cycle
	u16 level = (top+1) * duty / 100 -1; // calculate channel level from given duty cycle in %
	pwm_set_chan_level(slice_num, 0, level); 
	
	pwm_set_enabled(slice_num, true); // let's go!

	for(;;);
	return 0;
}

Hope that's useful to folks.

I see in the documentation that it's possible to double-buffer the duty cycle, too. I plan to exploit that capability. I'm impressed with the Pico's level of documentation.

Actually, you know what would be good? A Pico cookbook.

[nick.mccloud]

Hope that's useful to folks.

Saves me a job, thank you. Let the tunes begin.

Actually, you know what would be good? A Pico cookbook.

Perhaps a community effort on Git?

[blippy]

Hope that's useful to folks.

Saves me a job, thank you. Let the tunes begin. At the back of my mind is a whole synthesiser idea. My knowledge of electronics and DSP is woefully lacking, however, so there's a huge learning-curve on my behalf.

I have since learned that changes to the frequency and duty cycle of PWM waves are, in fact, double-buffered; which is exactly what I was hoping for.

I asked the team to incorporate this into the SDK, which they have done.

I think I'd hate to be on the engineering team with an awkward customer like me around

I guess it can be difficult, knowing which user suggestion is valuable, and which is a bit ... um .. dumbass.

I'm kinda excited by this whole Pico thing, though, because if the documentation blows all the other MCUs out of the market, then it offers a USP (Unique Selling Point) for the Pico.

Glad you liked it.

Actually, you know what would be good? A Pico cookbook.

Perhaps a community effort on Git?

Yeah. A wiki would work, too.

[nick.mccloud]

Perhaps a community effort on Git?

Yeah. A wiki would work, too.

A wiki on GitHub?

[HermannSW]

Perhaps a community effort on Git?

Yeah. A wiki would work, too.

A wiki on GitHub?

A PicoWikipedia?