Hello!
I am a beginner at nrf programming and have just started using the NCS and Zephyr on an nrf5340 evaluation board. I understand that Zephyr seems to be more or less a prerequisite right now when programming the nrf53 but I may have a problem.
I want to design a controller where I can to change the frequency of a PWM signal (50% duty cycle) based on the input value from an analog pin.
The change must be very fast. Ideally below 1uS
I tried a very simple example by modifying the LED_PWM code into just switching between a 0% and a 100% pulse as quickly as possible to see the delay:
/**
* @file Sample app to demonstrate PWM.
*/
#include <zephyr.h>
#include <sys/printk.h>
#include <device.h>
#include <drivers/pwm.h>
#define PWM_LED0_NODE DT_ALIAS(pwm_led0)
#if DT_NODE_HAS_STATUS(PWM_LED0_NODE, okay)
#define PWM_CTLR DT_PWMS_CTLR(PWM_LED0_NODE)
#define PWM_CHANNEL DT_PWMS_CHANNEL(PWM_LED0_NODE)
#define PWM_FLAGS DT_PWMS_FLAGS(PWM_LED0_NODE)
#else
#error "Unsupported board: pwm-led0 devicetree alias is not defined"
#define PWM_CTLR DT_INVALID_NODE
#define PWM_CHANNEL 0
#define PWM_FLAGS 0
#endif
#define MIN_PERIOD_USEC (USEC_PER_SEC / 64U)
#define MAX_PERIOD_USEC USEC_PER_SEC
void main(void)
{
const struct device *pwm;
uint32_t period;
int ret;
printk("PWM-based blinky\n");
pwm = DEVICE_DT_GET(PWM_CTLR);
if (!device_is_ready(pwm)) {
printk("Error: PWM device %s is not ready\n", pwm->name);
return;
}
period = 100000U;
while (1) {
ret = pwm_pin_set_usec(pwm, PWM_CHANNEL,
period, period, PWM_FLAGS);
ret = pwm_pin_set_usec(pwm, PWM_CHANNEL,
period, 0, PWM_FLAGS);
}
}
The switch time between a 100% pulse and a 0% pulse turns out to be more than 10ms when measured through oscilloscope. The delay is independent on any pulse length I set.
I assume this is due to the overhead within Zephyr or is there a way to improve this?
If not, is it possible to program the nrf53 application core directly as described in the datasheet - Setting the COUNTERTOP registry and basically bypassing Zephyr - at least for a snippet of code?
Many thanks for any assistance or pointers to examples.
/Jonas
