waveform generation problem

[ossmann]

I am currently testing the ESP32 waveform generator. I observe strong artefacts on DAC channel 1 for high frequencies. Do I do something wrong or is there a bug in the ESP32? I use the following program

Code: Select all

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"

#include "soc/rtc_io_reg.h"
#include "soc/rtc_cntl_reg.h"
#include "soc/sens_reg.h"
#include "soc/rtc.h"

#include "driver/dac.h"


/*
 * Generate a sine waveform on both DAC channels:
 *
 * DAC_CHANNEL_1 - GPIO25
 * DAC_CHANNEL_2 - GPIO26
 *
 * Connect scope to both GPIO25 and GPIO26
 * to observe the waveform changes
 * in response to the parameter change
*/

void app_main(){
  REG_SET_FIELD(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_CK8M_DIV_SEL, 7 );
  
  SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL1_REG, SENS_SW_TONE_EN);
  
  SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN1_M);
  SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN2_M);
  
  int scale=0 ;
  SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE1, scale, SENS_DAC_SCALE1_S);
  SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE2, scale, SENS_DAC_SCALE2_S);
  
  int invert=2 ;
  SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV1, invert, SENS_DAC_INV1_S);
  SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV2, invert, SENS_DAC_INV2_S);
			
  
  int frequency_step=0x1000 ;
  SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL1_REG, SENS_SW_FSTEP, frequency_step, SENS_SW_FSTEP_S);

  dac_output_enable(DAC_CHANNEL_1); // bad waveform
  dac_output_enable(DAC_CHANNEL_2);
 
}