Testing PWM implementation for esp8266
Just a quick entry to document my testing of this PWM library for the open esp8266 sdk.
The api is very simple:
/* Very basic example to test the pwm library
* Hook up an LED to pin14 and you should see the intensity change
*/
#include "espressif/esp_common.h"
#include "esp/uart.h"
#include "FreeRTOS.h"
#include "task.h"
#include "pwm.h"
void task1(void *pvParameters)
{
printf("Hello from task1!\r\n");
// XXX: duty cycle of zero crashes for me. skip for now
uint32_t const init_count = UINT16_MAX/16;
uint32_t count = init_count;
while(1) {
vTaskDelay(100);
printf("duty cycle set to %d/UINT16_MAX%%\r\n", count);
pwm_set_duty(count);
count += UINT16_MAX/16;
if (count > UINT16_MAX)
count = init_count;
}
}
void user_init(void)
{
uint8_t pins[1];
uart_set_baud(0, 115200);
printf("SDK version:%s\n", sdk_system_get_sdk_version());
printf("pwm_init(1, [14])\n");
pins[0] = 14;
pwm_init(1, pins);
printf("pwm_set_freq(1000) # 1 kHz\n");
pwm_set_freq(1000);
printf("pwm_set_duty(UINT16_MAX/2) # 50%%\n");
pwm_set_duty(UINT16_MAX/2);
printf("pwm_start()\n");
pwm_start();
xTaskCreate(task1, (signed char *)"tsk1", 256, NULL, 2, NULL);
}
And two snapshots from GPIO14 taken with the logic analyzer while the above test was running.
6.25% duty cycle | 68.65% duty cycle |
---|---|
Issues
- The library crashes when the duty cycle is set to 0 (
pwm_set_duty(0)
). It is probably a problem with the underlying timers, but I would suggest detecting that in thepwm_set_duty()
function and just call pwm_stop(). -
When setting the duty cycle to 100%, the output is not truly 100% (i.e. constant high) but rather 99.65% I would also suggest to detect that scenario in
pwm_set_duty()
and set the output to constant high. - The library/target does not work at high frequencies. When setting the frequency to 50kHz the observed output is 40kHz.
- Every change of duty cycle resets the output to HIGH. This might introduce glitches in applications where the duty cycle changes frequently (e.g. audio)
Written on November 28, 2015