一、概述

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。

设备树配置

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

二、命令行

1.echo 0 > /sys/class/pwm/pwmchip0/export /*设置PWM4输出，调出pwm0目录下设备节点，用于以下配置 */

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 /*设置PWM4一个周期的持续时间，单位为ns，即1K Hz */
3.echo 500000 >/sys/class/pwm/pwmchip0/pwm0/duty_cycle /*设置一个周期中的”ON”时间，单位为ns，即占空比=duty_cycle/period=50% */
4.echo 1 >/sys/class/pwm/pwmchip0/pwm0/enable /*设置PWM4使能 */

OK，灯亮了！

三、用户空间应用代码测试

#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" /*ns*/  
#define SYSFS_PWM0_DUTY_CYCLE      "/sys/class/pwm/pwmchip0/pwm0/duty_cycle"
#define SYSFS_PWM0_DUTY_CYCLE_VAL  "500000" /*ns*/ 

#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;
}