PWM使用说明

这篇文档主要介绍如何使用硬件PWM，VIM4PWM_F端口默认被其它功能占用，使用PWM_F端口前，请先修改如下代码：

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diff --git a/arch/arm64/boot/dts/amlogic/kvim4.dts b/arch/arm64/boot/dts/amlogic/kvim4.dts
--- a/arch/arm64/boot/dts/amlogic/kvim4.dts
+++ b/arch/arm64/boot/dts/amlogic/kvim4.dts
@@ -1749,13 +1749,13 @@
                };
        };
 
-       bl1_pwm_off_pins:bl1_pwm_off_pin {
-               mux {
-                       groups = "GPIOY_8";
-                       function = "gpio_periphs";
-                       output-low;
-               };
-       };
 

diff --git a/arch/arm64/boot/dts/amlogic/mesont7_an400-panel.dtsi b/arch/arm64/boot/dts/amlogic/mesont7_an400-panel.dtsi
--- a/arch/arm64/boot/dts/amlogic/mesont7_an400-panel.dtsi
+++ b/arch/arm64/boot/dts/amlogic/mesont7_an400-panel.dtsi
@@ -1442,13 +1442,13 @@
 
        backlight1{
                compatible = "amlogic, backlight-t7";
-               status = "okay";
+               status = "disabled";
                index = <1>;
                key_valid = <0>;
                pinctrl-names = "pwm_on",
                                "pwm_off";
-               pinctrl-0 = <&pwm_f_pins>;
-               pinctrl-1 = <&bl1_pwm_off_pins>;
                pinctrl_version = <2>; /* for uboot */
                interrupts = <0 197 1

PWM_F物理引脚确认

PWM使用

  • 申请PWM
    1
    root@Khadas:~# echo 1 > /sys/class/pwm/pwmchip4/export
  • 配置PWM周期
    1
    root@Khadas:~# echo 1000000 > /sys/class/pwm/pwmchip4/pwm1/period
  • 配置PWM占空比
    1
    root@Khadas:~# echo 500000 > /sys/class/pwm/pwmchip4/pwm1/duty_cycle
  • 使能PWM
    1
    root@Khadas:~# echo 1 > /sys/class/pwm/pwmchip4/pwm1/enable
  • 关闭PWM
    1
    root@Khadas:~# echo 0 > /sys/class/pwm/pwmchip4/pwm1/enable

如果你成功开启了硬件PWM，可以通过示波器看到波形：

pwm-Oscilloscope

注意

如果使用示波器去查看波形，记得板子和示波器需要共地。