嵌入式Linux：使用sysfs控制PWM

• 一、概述
• • 设备树配置
• 二、命令行
• 三、用户空间应用代码测试
• 四、Qt+触摸屏+滑块+灯亮度变化

从上一篇嵌入式Linux：Qt5+触摸屏+点灯（使用sysfs控制gpio）第一次使用了sysfs控制GPIO现在使用同样的方式控制PWM。

配置sun8i-v3s.dtsi

pwm0_pins: pwm0 {
                pins = "PB4";
                function = "pwm0";
        };

        pwm1_pins: pwm1{
                pins = "PB5";
                function = "pwm1";
        };

pwm: pwm@1c21400 {
                  compatible = "allwinner,sun8i-v3s-pwm",
                               "allwinner,sun7i-a20-pwm";
                  reg = <0x01c21400 0x400>;
                  clocks = <&osc24M>;
                  #pwm-cells = <3>;
                  status = "okay";
          };

配置sun8i-v3s-licheepi-zero.dts

&pwm{
        pinctrl-names = "default";
        pinctrl-0     = <&pwm0_pins>,<&pwm1_pins>;
        status        = "okay";
};

上电运行，目录下查看：

# cd /sys/class/pwm
# ls
pwmchip0

• 1.echo 0 > /sys/class/pwm/pwmchip0/export

运行命令前

device     export     npwm       power      subsystem  uevent     unexport

运行命令后

device     npwm       pwm0       uevent export     power      subsystem  unexport

• 2.echo 1000000 >/sys/class/pwm/pwmchip0/pwm0/period

• 3.echo 500000 >/sys/class/pwm/pwmchip0/pwm0/duty_cycle

• 4.echo 1 >/sys/class/pwm/pwmchip0/pwm0/enable

OK，灯亮了！

#include "stdlib.h"  
#include "stdio.h"  
#include "string.h"
#include "unistd.h"
#include "fcntl.h"   //define O_WRONLY and O_RDONLY  

//user_pin: PB4
#define SYSFS_PWM_EXPORT           "/sys/class/pwm/pwmchip0/export"  
#define SYSFS_PWM0                 "0"
#define SYSFS_PWM1                 "1" 
#define SYSFS_PWM0_STATE           "/sys/class/pwm/pwmchip0/pwm0/enable"
#define SYSFS_PWM1_STATE           "/sys/class/pwm/pwmchip0/pwm1/enable"

#define SYSFS_PWM0_PERIOD          "/sys/class/pwm/pwmchip0/pwm0/period"
#define SYSFS_PWM0_PERIOD_VAL      "1000000"   
#define SYSFS_PWM0_DUTY_CYCLE      "/sys/class/pwm/pwmchip0/pwm0/duty_cycle"
#define SYSFS_PWM0_DUTY_CYCLE_VAL  "500000"  

#define SYSFS_PWM_EANBLE           "1"
#define SYSFS_PWM_DISANBLE         "0"


int main() 
{ 
    int fd; 
	
	//使能PWM0：echo 0 > /sys/class/pwm/pwmchip0/export
	fd = open(SYSFS_PWM_EXPORT, O_WRONLY);
	if(fd == -1)
	{
		printf("ERR: PWM pin open error.n");
		return EXIT_FAILURE;
	}
	write(fd, SYSFS_PWM0 ,sizeof(SYSFS_PWM0)); 
	close(fd); 

	//设置周期：echo 1000000 > /sys/class/pwm/pwmchip0/pwm0/period
	fd = open(SYSFS_PWM0_PERIOD, O_RDWR);
	if(fd == -1)
	{
		printf("ERR: PWM period direction open error.n");
		return EXIT_FAILURE;
	}
	write(fd, SYSFS_PWM0_PERIOD_VAL, sizeof(SYSFS_PWM0_PERIOD_VAL)); 
	close(fd); 

	//设置占空比: echo 500000 > /sys/class/pwm/pwmchip0/pwm0/duty_cycle
	fd = open(SYSFS_PWM0_DUTY_CYCLE, O_RDWR);
	if(fd == -1)
	{
		printf("ERR: PWM duty cycle pin value open error.n");
		return EXIT_FAILURE;
	} 
	write(fd, SYSFS_PWM0_DUTY_CYCLE_VAL, sizeof(SYSFS_PWM0_DUTY_CYCLE_VAL)); 
	close(fd); 

	// 使能PWM通道：echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable
	fd = open(SYSFS_PWM0_STATE, O_RDWR);
	if(fd == -1)
	{
		printf("ERR: pwm open error.n");
		return EXIT_FAILURE;
	}
	while(1)
	{
		write(fd, SYSFS_PWM_EANBLE, sizeof(SYSFS_PWM_EANBLE));
		usleep(1000000);
		write(fd, SYSFS_PWM_DISANBLE, sizeof(SYSFS_PWM_DISANBLE));
		usleep(1000000);
	}
	close(fd);

	printf("INFO: PWM pin value open error.n");
	return 0;
}  

编译代码

arm-linux-gnueabihf-gcc pwm.c -o pwm

拷贝到开发板运行代码

./pwm

板子上的灯动起来了：一秒钟亮暗！

核心Qt代码：

void MainWindow::execCmd1(int duty)
{
    QString path = PWM_LED_PATH;
    
    
    QString cmd_config = "echo 0 > /sys/class/pwm/pwmchip0/export";
    QByteArray cmdby_off = cmd_config.toLatin1();
    char* charCmd_config = cmdby_off.data();
    system(charCmd_config);

    
    QString cmd_period = "echo 10000 > /sys/class/pwm/pwmchip0/pwm0/period";
    QByteArray cmdby_period = cmd_period.toLatin1();
    char* charCmd_period = cmdby_period.data();
    system(charCmd_period);

    
    QString cmd_duty = "echo "+ QString::number(duty, 10) +" > /sys/class/pwm/pwmchip0/pwm0/duty_cycle";
    QByteArray cmdby_duty = cmd_duty.toLatin1();
    char* charCmd_duty = cmdby_duty.data();
    system(charCmd_duty);

    
    QString cmd_enable = "echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable";
    QByteArray cmdby_enable = cmd_enable.toLatin1();
    char* charCmd_enable = cmdby_enable.data();
    system(charCmd_enable);
}
// 滑块配置灯的亮度
void MainWindow::on_horizontalSlider_valueChanged(int value)
{
    ui->label->setText(QString::number(value));

    execCmd1(value);
}