ESP32-C3 trying to output 40MHz on GPIO10

[espmich]

In order to probe the crystal frequency without touching it, I want to create a periodic wave on GPIO10 to measure using my frequency counter. This is commonplace in other MCUs with a MCO (master clock output) function.

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#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/ledc.h"
#include "esp_err.h"

void app_main() {
    // Configure the LEDC timer
    ledc_timer_config_t timer_conf;
    timer_conf.speed_mode = LEDC_LOW_SPEED_MODE;
    timer_conf.duty_resolution = LEDC_TIMER_1_BIT;
    timer_conf.timer_num = LEDC_TIMER_0;
    timer_conf.freq_hz = 40000000;
    //timer_conf.clk_cfg = APB_CLK;
    timer_conf.clk_cfg = LEDC_USE_XTAL_CLK;
    timer_conf.deconfigure = false;
    ledc_timer_config(&timer_conf);

    // Configure the LEDC channel
    ledc_channel_config_t channel_conf;
    channel_conf.gpio_num = 10; // Pin 16 GPIO-10
    channel_conf.speed_mode = LEDC_LOW_SPEED_MODE;
    channel_conf.channel = LEDC_CHANNEL_0;
    channel_conf.intr_type = LEDC_INTR_DISABLE;
    channel_conf.timer_sel = LEDC_TIMER_0;
    channel_conf.duty = 0;
    channel_conf.hpoint = 0;
    ledc_channel_config(&channel_conf);

    // Start the output
    ledc_update_duty(LEDC_LOW_SPEED_MODE, LEDC_CHANNEL_0);

    // Keep the task running
    while (1) {
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

Unfortunately when I program the ESP32-C3 chip with the above code, it fails to ouput a periodic wave on GPIO10. I'm not sure what is wrong, want to take a look?

[Sprite]

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    //timer_conf.clk_cfg = APB_CLK;
    timer_conf.clk_cfg = LEDC_USE_XTAL_CLK;

You cannot get a 40MHz signal from the LEDC if you use the XTAL clock. Does it also not work if you use the APB clock?

[espmich]

Before seeing your reply I tried switching code to the:

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esp-idf/examples/peripherals/ledc/ledc_basic

project. I was able to generate 4KHz signal but at 40KHz the MCU fails again, and of course 4MHz fails as you mentioned.

This project uses:

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ledc_timer.clk_cfg = LEDC_AUTO_CLK

Actually all these clock optoins confuse me. I changed the above line to:

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ledc_timer.clk_cfg = LEDC_USE_APB_CLK

...and will now try to test it again with a frequency counter. Please stay tuned.

[espmich]

In case the LEDC peripheral is totally incapable of generating a clean 40MHz signal, what other options are there to do this?

[espmich]

I tested the LEDC peripheral as described above, using the LEDC_USE_APB_CLK but it failed at about 9-10KHz.

I'm confused, can the ESP chips not output a stable high frequency signal?

[espmich]

Any idea how to generate a 40 MHz signal, can a hardware timer be used or some configuration value in LEDC?

[Sprite]

That does not sound right. What frequency counter and what setup are you using?

[espmich]

The frequency counter I'm using to measure the ESP32-C3 is the same one I use to measure all the STM32 MCUs successfully. It is an Philips PM-6672 with a standard (oscilloscope style) probe:

https://www.archive.org/details/manual_ ... OM_PHILIPS

This device indicates the frequency correctly on my ESP32-C3, whenever I set the MCU LEDC peripheral to output at 4KHz.

What I already did:

• 1) Use Google search and copy the AI answer provided, real source code.
  2) Use the LEDC basic example in the ESP-IDF 5.42 development environment.
  3) Adjust #2 above to use Sprite TM's suggestion changing the clock to try all (AUTO, XTAL, APB) clocks.

Would you @Sprite please show example code here that is reasonably expected to work correctly? Please assume the GPIO10 (pin 16 on a ESP32-C3FH4 chip) as output. Thank you!

[Sprite]

- Using ESP-IDF v5.4.2
- Using an ESP32-C3-DevkitM-1 v1.0
- Example examples/peripherals/ledc/ledc_basic
- Modify main/ledc_basic_example_main.c as such:

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#define LEDC_OUTPUT_IO          (10) // Define the output GPIO
#define LEDC_DUTY_RES           LEDC_TIMER_1_BIT // Set duty resolution to 1 bit
#define LEDC_FREQUENCY          (40000000) // Frequency in Hertz. Set frequency at 40MHz

- Probing GPIO10:

RigolDS5.png (95.9 KiB) Viewed 319 times

Given that I get a proper 40MHz, I'd imagine there may be something wrong with your setup. Do you have something else (a logic analyzer or an oscilloscope, for instance) that can verify your measurement?

[espmich]

Thanks @Sprite and everything is working after your LEDC suggestion.

It appears my AI generated code set the duty cycle to 0 (should be 4096) and I had not modified the ESP-IDF LECD basic sample from LEDC_TIMER_13_BIT to LEDC_TIMER_1_BIT resolution. Nothing was working with those mistakes.