Rock pi 4 是否支持读取pwm？

#1

我试着短接11与13脚
11脚运行官方的mraa pwm.c示例,如下

/*
 * Author: Thomas Ingleby <thomas.c.ingleby@intel.com>
 * Contributors: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
 * Copyright (c) 2014 Intel Corporation.
 *
 * SPDX-License-Identifier: MIT
 *
 * Example usage: Generates PWM signal of period 200us with variable dutycyle
 *                repeately. Press Ctrl+C to exit
 */

/* standard headers */
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

/* mraa header */
#include "mraa/pwm.h"

/* PWM declaration */
#define PWM 11

/* PWM period in us */
#define PWM_FREQ 200

volatile sig_atomic_t flag = 1;

void
sig_handler(int signum)
{
    if (signum == SIGINT) {
        fprintf(stdout, "Exiting...\n");
        flag = 0;
    }
}

int
main(void)
{
    mraa_result_t status = MRAA_SUCCESS;
    mraa_pwm_context pwm;
    float value = 0.0f;
    float output;

    /* initialize mraa for the platform (not needed most of the times) */
    mraa_init();

    //! [Interesting]
    pwm = mraa_pwm_init(PWM);
    if (pwm == NULL) {
        fprintf(stderr, "Failed to initialize PWM\n");
        mraa_deinit();
        return EXIT_FAILURE;
    }

    /* set PWM period */
    status = mraa_pwm_period_us(pwm, PWM_FREQ);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* enable PWM */
    status = mraa_pwm_enable(pwm, 1);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while (flag) {
        value = value + 0.01f;

        /* write PWM duty cyle */
        status = mraa_pwm_write(pwm, value);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        usleep(50000);

        if (value >= 1.0f) {
            value = 0.0f;
        }

        /* read PWM duty cyle */
        output = mraa_pwm_read(pwm);
        fprintf(stdout, "PWM value is %f\n", output);
    }

    /* close PWM */
    mraa_pwm_close(pwm);

    //! [Interesting]
    /* deinitialize mraa for the platform (not needed most of the times) */
    mraa_deinit();

    return EXIT_SUCCESS;

err_exit:
    mraa_result_print(status);

    /* close PWM */
    mraa_pwm_close(pwm);

    /* deinitialize mraa for the platform (not needed most of the times) */
    mraa_deinit();

    return EXIT_FAILURE;
}

13脚运行基于官方改的读取pwm的c,如下

/*
 * Author: Thomas Ingleby <thomas.c.ingleby@intel.com>
 * Contributors: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
 * Copyright (c) 2014 Intel Corporation.
 *
 * SPDX-License-Identifier: MIT
 *
 * Example usage: Generates PWM signal of period 200us with variable dutycyle
 *                repeately. Press Ctrl+C to exit
 */

/* standard headers */
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

/* mraa header */
#include "mraa/pwm.h"

/* PWM declaration */
#define PWM 13

/* PWM period in us */
#define PWM_FREQ 200

volatile sig_atomic_t flag = 1;

void
sig_handler(int signum)
{
    if (signum == SIGINT) {
        fprintf(stdout, "Exiting...\n");
        flag = 0;
    }
}

int
main(void)
{
    mraa_result_t status = MRAA_SUCCESS;
    mraa_pwm_context pwm;
    float value = 0.0f;
    float output;

    /* initialize mraa for the platform (not needed most of the times) */
    mraa_init();

    //! [Interesting]
    pwm = mraa_pwm_init(PWM);
    if (pwm == NULL) {
        fprintf(stderr, "Failed to initialize PWM\n");
        mraa_deinit();
        return EXIT_FAILURE;
    }

    /* set PWM period */
    status = mraa_pwm_period_us(pwm, PWM_FREQ);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* enable PWM */
    status = mraa_pwm_enable(pwm, 1);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while (flag) {
        /* value = 0.01f;

        write PWM duty cyle
        status = mraa_pwm_write(pwm, value);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        usleep(1000000);

        if (value >= 1.0f) {
            value = 0.0f;
        } */
        usleep(1000000);
        /* read PWM duty cyle */
        output = mraa_pwm_read(pwm);
        fprintf(stdout, "PWM value is %f\n", output);
    }

    /* close PWM */
    mraa_pwm_close(pwm);

    //! [Interesting]
    /* deinitialize mraa for the platform (not needed most of the times) */
    mraa_deinit();

    return EXIT_SUCCESS;

err_exit:
    mraa_result_print(status);

    /* close PWM */
    mraa_pwm_close(pwm);

    /* deinitialize mraa for the platform (not needed most of the times) */
    mraa_deinit();

    return EXIT_FAILURE;
}

运行结果如下

chen@rockpi4b:~/examples/c/pwm$ sudo ./pwm_in
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
PWM value is 0.000000
^C
chen@rockpi4b:~/examples/c/pwm$
#2

/**

  • Read the output duty-cycle percentage, as a float

  • @param dev The Pwm context to use

  • @return percentage A floating-point value representing percentage of output.

  • The value should lie between 0.0f (representing on 0%) and 1.0f

  • Values above or below this range will be set at either 0.0f or 1.0f

*/

float mraa_pwm_read(mraa_pwm_context dev);
好吧，看起来这个方法只能读取输出的占空比，是否有其他方法实现读取pwm波？我目前想到的是gpio+算法