MX6UL如何修改PWM输出
采用lcd电阻触摸一路GPIO1_IO04用作PWM控制，并输出2.4K的方波。
CPU默认可输出8路PWM，默认背光采用的为PWM1，增加GPIO1_IO04复用为PWM3。
驱动默认已经加载，驱动路径为drivers/pwm/pwm-imx.c。
修改设备树，修改imx6ul.dtsi中
pwm3: pwm@02088000 {
compatible = "fsl,imx6ul-pwm", "fsl,imx27-pwm";
reg = <0x02088000 0x4000>;
interrupts = <GIC_SPI 85IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_DUMMY>,
<&clks IMX6UL_CLK_DUMMY>;
clock-names = "ipg", "per";
#pwm-cells = <2>;
};
为
pwm3: pwm@02088000 {
compatible = "fsl,imx6ul-pwm", "fsl,imx27-pwm";
reg = <0x02088000 0x4000>;
interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_PWM3>,
<&clks IMX6UL_CLK_PWM3>;
clock-names = "ipg", "per";
#pwm-cells = <2>;
};
在imx6ul-14x14-evk.dts中添加：
&pwm3 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_pwm3>;
status = "okay";
};
添加pinctl_pwm3
pinctrl_pwm3: pwm3grp {
fsl,pins = <
MX6UL_PAD_GPIO1_IO04__PWM3_OUT 0x110b0
>;
};
并将GPIO1_IO04其他复用的地方取消或者注释掉。
tsc中status = “disabled”;
编译设备树，替换开发板中设备树，并选择此设备树。
在开发板启动之后，命令行输入：
root@freescale ~$ echo 0 > /sys/class/pwm/pwmchip2/export
root@freescale ~$ echo 1 >/sys/class/pwm/pwmchip2/pwm0/enable
root@freescale ~$ echo 416667 > /sys/class/pwm/pwmchip2/pwm0/period
root@freescale ~$ echo 208333 > /sys/class/pwm/pwmchip2/pwm0/duty_cycle
此时GPIO1_IO04输出2.4K方波。
如果输出1KHz方波，命令如下：
root@freescale ~$echo 1000000 > /sys/class/pwm/pwmchip1/pwm0/period
root@freescale ~$echo 500000 > /sys/class/pwm/pwmchip1/pwm0/duty_cycle
