【驱动篇】龙芯LS2K0300之PWM设备驱动

实验目的

利用脉冲调制效应（PWM）等效改变输出功率大小控制LED，从而实现呼吸灯效果，需要用到RGB LED模块

模块连接

IO 插针接口上一共集成了两路PWM，分别是PWM2和PWM3，对应GPIO88、GPIO89
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PWM2和PWM3对应Pin3和Pin5引脚，这里使用Pin1和Pin3分别连接LED的GND和R口
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修改设备树

arch/loongarch/boot/dts/loongson/loongson_2k0300.dtsi

pwm2: pwm@0x1611b020 {
    compatible = "loongson,ls2k-pwm";
    reg = <0 0x1611b020 0 0xf>;
    interrupt-parent = <&icu>;
    interrupts = <17>;
    #pwm-cells = <2>;
    clock-frequency = <100000000>;
    status = "disabled";
};

pwm3: pwm@0x1611b030 {
    compatible = "loongson,ls2k-pwm";
    reg = <0 0x1611b030 0 0xf>;
    interrupt-parent = <&icu>;
    interrupts = <17>;
    #pwm-cells = <2>;
    clock-frequency = <100000000>;
    status = "disabled";
};

arch/loongarch/boot/dts/loongson/2k0300-pinctrl.dtsi

pwm2_pin: pwm2-pin{
    pwm2_mux_m0: pwm2-mux-m0{
        loongson,pinmux = <&gpa4 2 2>;
        loongson,pinmux-funcsel = <PINCTL_FUNCTION1>;
    };
    pwm2_mux_m1: pwm2-mux-m1{
        loongson,pinmux = <&gpa5 8 8>;              	/* pwm2 have two multiplex methods */
        loongson,pinmux-funcsel = <PINCTL_FUNCTION2>;
    };
};

pwm3_pin: pwm3-pin{
    pwm3_mux_m0: pwm3-mux-m0{
        loongson,pinmux = <&gpa4 3 3>;
        loongson,pinmux-funcsel = <PINCTL_FUNCTION1>;
    };
    pwm3_mux_m1: pwm3-mux-m1{							/* pwm3 have two multiplex methods */
        loongson,pinmux = <&gpa5 9 9>;
        loongson,pinmux-funcsel = <PINCTL_FUNCTION2>;
    };
};

arch/loongarch/boot/dts/loongson/loongson_2k0300_pai_99.dts

&pwm2{
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&pwm2_mux_m1>;
};
&pwm3{
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&pwm3_mux_m1>;
};

修改完毕后重新编译内核，将内核部署到开发板/boot目录下，重启开发板发现/sys/class/pwm下已经生成两个pwmchip节点

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波形测试

运行测试脚本run.sh，周期和占空比脉冲的时间单位为ns

echo 0 > /sys/class/pwm/pwmchip0/export					# 导出pwm节点
echo 0 > /sys/class/pwm/pwmchip0/pwm0/enable			# 关闭pwm输出
echo 100000 > /sys/class/pwm/pwmchip0/pwm0/period		# 设置pwm周期
echo 50000 > /sys/class/pwm/pwmchip0/pwm0/duty_cycle	# 设置占空比脉冲数
echo "normal" > /sys/class/pwm/pwmchip0/pwm0/polarity	# 设置极性，有normal和inversed两种
echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable			# 开启pwm输出

示波器查看PWM2输出波形：生成了10KHz的波形，占空比为50%

在这里插入图片描述

PWM LED模拟呼吸灯效果，为了简单起见就不写C语言代码了

num=10
peroid=100000
max=100000
min=10
flag=0

echo $peroid > /sys/class/pwm/pwmchip0/pwm0/period

while true
do
	if [ $flag -eq 0 ]
	then 
		if [ $num -lt $max ]
		then  
			echo 0 > /sys/class/pwm/pwmchip0/pwm0/enable
#			echo $peroid > /sys/class/pwm/pwmchip0/pwm0/period
			echo $num > /sys/class/pwm/pwmchip0/pwm0/duty_cycle
			echo "normal" > /sys/class/pwm/pwmchip0/pwm0/polarity
			echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable
			sleep 0.1
			let num+=10000	
		else
			flag=1
		fi
	else
		if [ $num -gt $min ]
		then  
			echo 0 > /sys/class/pwm/pwmchip0/pwm0/enable
#			echo $peroid > /sys/class/pwm/pwmchip0/pwm0/period
			echo $num > /sys/class/pwm/pwmchip0/pwm0/duty_cycle
			echo "normal" > /sys/class/pwm/pwmchip0/pwm0/polarity
			echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable
			sleep 0.1
			let num-=10000
		else
			flag=0
		fi	
	fi	
done