[solved] Setting RTC register bits fails (ESP32-S3)

[cbaurtx]

I want to initialize the RTC I2C controller using the main processor of the ESP32-S3
As en example setting RTC_I2C_SCL_LOW_REG

SET_PERI_REG_BITS(RTC_I2C_SCL_LOW_REG, RTC_I2C_SCL_LOW_PERIOD_REG, 40, RTC_I2C_SCL_LOW_PERIOD_REG_S); // SCL low/high period = 40, which result driving SCL with 100kHz.
ESP_LOGI(TAG, "RTC_I2C_SCL_LOW_REG = %d", READ_PERI_REG(RTC_I2C_SCL_LOW_REG));

When executing the code the read back returns the default value (256) and not the set value (40).

I use IDF which is part of an ADF installation, IDF Version v4.4-dev-5980-g3c8bc2213c-dirty ADF Version v2.6

[Sprite]

Hm, that smells like that peripheral or power domain is not enabled. The RTC I2C peripheral is part of the ULP coprocessor; you can see if you somehow can enable that and if that makes the register writable.

[cbaurtx]

Thank you for answering that quickly. What you said makes a lot of sense, however I can
use the RTC GPIO without any problems. How can I turn the RTC power domain on or off to
double check?

[cbaurtx]

Code: Untitled.c Select all

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "freertos/FreeRTOS.h"

#include "freertos/task.h"



#define TAG "test_write_rtc_reg.c"



#if ESP_IDF_VERSION_MAJOR < 5

  #include "driver/rtc_cntl.h"

#else

  #include "esp_private/rtc_ctrl.h"

#endif



#include "driver/rtc_io.h"

#include "soc/rtc_i2c_reg.h"

#include "esp_log.h"



int app_main(void) {

#if CONFIG_IDF_TARGET_ESP32

  #pragma message "IDF Target ESP32"



  SET_PERI_REG_BITS(RTC_I2C_SCL_LOW_PERIOD_REG, RTC_I2C_SCL_LOW_PERIOD, 40, RTC_I2C_SCL_LOW_PERIOD_S);

  ESP_LOGI(TAG, "ESP32 RTC_I2C_SCL_LOW_REG =  %d", READ_PERI_REG(RTC_I2C_SCL_LOW_PERIOD_REG));



  SET_PERI_REG_BITS(RTC_I2C_SCL_LOW_PERIOD_REG, RTC_I2C_SCL_LOW_PERIOD, 20, RTC_I2C_SCL_LOW_PERIOD_S);

  ESP_LOGI(TAG, "ESP32 RTC_I2C_SCL_LOW_REG =  %d", READ_PERI_REG(RTC_I2C_SCL_LOW_PERIOD_REG));



#endif





#if CONFIG_IDF_TARGET_ESP32S3

  #pragma message "IDF Target ESP32-S3"



  SET_PERI_REG_BITS(RTC_I2C_SCL_LOW_REG, RTC_I2C_SCL_LOW_PERIOD_REG_M, 40, RTC_I2C_SCL_LOW_PERIOD_REG_S);

  ESP_LOGI(TAG, "ESP32S3 RTC_I2C_SCL_LOW_REG =  %d", READ_PERI_REG(RTC_I2C_SCL_LOW_REG));



  SET_PERI_REG_BITS(RTC_I2C_SCL_LOW_REG, RTC_I2C_SCL_LOW_PERIOD_REG, 20, RTC_I2C_SCL_LOW_PERIOD_REG_S);

  ESP_LOGI(TAG, "ESP32S3 RTC_I2C_SCL_LOW_REG =  %d", READ_PERI_REG(RTC_I2C_SCL_LOW_REG));



#endif



for(;;);



}

I did some more tests. This code works with an ESP32 but not with an ESP32-S3
With the ESP32-S3 the default value is returned. How are the default values set?

[cbaurtx]

Finally I got it working and I blame poor documentation for my problem. Looking how the RiskV ULP initializes the rtc i2c I found this:

Code: Select all

/* For esp32s3, we need to enable the rtc_i2c clock gate before accessing rtc i2c    registers */
  SET_PERI_REG_MASK(SENS_SAR_PERI_CLK_GATE_CONF_REG, SENS_RTC_I2C_CLK_EN);

So insert this at line 34 and the rtc register can be set

[Sprite]

Finally I got it working and I blame poor documentation for my problem.

I entirely agree, I'll see if I can poke the documentation team to include this information in future releases. EDIT: Seems that chapter is the very last chapter in the TRM that is missing. People are working on it.