ESP32 changing clock frequency (C) - c

Question

I am programming an ESP32 with C (with the toolchain for ESP32) and I'm trying to change the clock frequency of my ESP32 but I'm quite unsure if I'm doing it right (I used the documenation https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/power_management.html#_CPPv418esp_pm_lock_type_t but I didn't find any code examples). I think I've done the program part right but I think it still doesn't work. Is there a way to figure out the the clock frequency that is set?
I'm also unsure about this part in documentation:
"ESP_PM_CPU_FREQ_MAX
Require CPU frequency to be at the maximum value set via esp_pm_configure. Argument is unused and should be set to 0."
Does the last part mean I shouldn't use this makro?
Last but not least I didnt't understand if I have to change my sdkconfig or is there a way to do everything in C?
I have to measure for a project times in region of ns hence I need maximum performance of esp32.
Code:
// ____________________________________________________________________________
esp_pm_config_esp32_t config_clock_struct;
// ____________________________________________________________________________
esp_pm_config_esp32_t* pointer_config_clock = &config_clock_struct;
// ____________________________________________________________________________
esp_pm_lock_handle_t handle;
void config_clock(int max_cpu_freq, int min_cpu_freq, bool light_sleep_enable,
esp_pm_config_esp32_t* pointer_config_clock) {
pointer_config_clock->max_freq_mhz = max_cpu_freq;
pointer_config_clock->min_freq_mhz = min_cpu_freq;
pointer_config_clock->light_sleep_enable = light_sleep_enable;
esp_err_t status = esp_pm_configure(pointer_config_clock);
if (status == ESP_OK) {
return;
} else if (status == ESP_ERR_INVALID_ARG) {
printf("Error %d: Configuration values aren't correct.", status);
exit(1);
} else if (status == ESP_ERR_NOT_SUPPORTED) {
printf("Error %d: Combination of values aren't supported or CONFIG_PM_ENABLE isn't enabled in sdkconfig.",
status);
exit(1);
}
}
// ____________________________________________________________________________
void init_clock(int max_cpu_freq, int min_cpu_freq, bool light_sleep_enable,
esp_pm_lock_type_t lock_type, int arg, const char* name,
esp_pm_config_esp32_t* pointer_config_clock, esp_pm_lock_handle_t* out_handle) {
config_clock(max_cpu_freq, min_cpu_freq, light_sleep_enable, pointer_config_clock);
esp_err_t status = esp_pm_lock_create(lock_type, arg, name, out_handle);
if (status == ESP_OK) {
return;
} else if (status == ESP_ERR_NO_MEM) {
printf("Error %d: Struct can't allocated.", status);
} else if (status == ESP_ERR_INVALID_ARG) {
printf("Error: %d: Invalid arguments.", status);
} else if(ESP_ERR_NOT_SUPPORTED == status) {
printf("Error %d: config pm is not enabled in sdkconfig.", status);
}
}
And the relevant part of the main function:
#define MAX_FREQUENCY 240
#define MIN_FREQUENCY 40
#define DISABLE_SLEEP 0
init_clock(MAX_FREQUENCY, MIN_FREQUENCY, DISABLE_SLEEP, ESP_PM_CPU_FREQ_MAX, ESP_PM_CPU_FREQ_MAX,
"measure mode", pointer_config_clock, &handle);
esp_err_t status_acquire = esp_pm_lock_acquire(handle);

Answer 1

When one changes MCU clock frequency it alters all frequency dependent buses. For instance UART and I2C. Here's a neat hack to demonstrate how changing of clock frequency affects serial.print output. Mind you calculated Serial baud rates differ for each clock speed set.
//function takes the following frequencies as valid values:
// 240, 160, 80 <<< For all XTAL types
// 40, 20, 10 <<< For 40MHz XTAL
// 26, 13 <<< For 26MHz XTAL
// 24, 12 <<< For 24MHz XTAL
// 32Bit MCUs . change for 16bit
uint32_t Freq = 0;
int MCU_FREQUENCY_SERIAL_SPEED=115200;
int SERIAL_DEFAULT_SPEED = 115200;
void changeMcuFreq(int Freq){
delay(500);
setCpuFrequencyMhz(Freq);
changeSerialBaudRate(Freq);
delay(500);
}
void serialMcuFreq(){
Freq = getCpuFrequencyMhz();
Serial.print("CPU Freq = ");
Serial.print(Freq);
Serial.println(" MHz");
Freq = getXtalFrequencyMhz();
Serial.print("XTAL Freq = ");
Serial.print(Freq);
Serial.println(" MHz");
Freq = getApbFrequency();
Serial.print("APB Freq = ");
Serial.print(Freq/1000000);
Serial.println(" MHz");
}
void changeSerialBaudRate(uint32_t Freq){
if (Freq < 80) {
MCU_FREQUENCY_SERIAL_SPEED = 80 / Freq * SERIAL_DEFAULT_SPEED;
}
else {
MCU_FREQUENCY_SERIAL_SPEED = SERIAL_DEFAULT_SPEED;
}
Serial.end();
delay(1000);
Serial.begin(MCU_FREQUENCY_SERIAL_SPEED);
delay(1000);
Serial.print("\nSerial Baud Rate Speed is ");
Serial.println(MCU_FREQUENCY_SERIAL_SPEED);
}
void setup()
{
Serial.begin(MCU_FREQUENCY_SERIAL_SPEED);
}
void loop()
{
changeMcuFreq(240);
serialMcuFreq();
delay(2000);
changeMcuFreq(160);
serialMcuFreq();
delay(2000);
changeMcuFreq(80);
serialMcuFreq();
delay(2000);
changeMcuFreq(40);
serialMcuFreq();
delay(2000);
changeMcuFreq(20);
serialMcuFreq();
delay(2000);
changeMcuFreq(10);
serialMcuFreq();
delay(2000);
}