本文讲解了国产A40i 开发板PWM的应用，本篇文章主要适用于飞凌 OKA40i 平台 Linux3.10.65 操作系统，其他arm 平台也可以参考，但是不同平台之间会存在差异，请自行修改以适应自己的使用。 写本文章的主要目的是协助客户加速产品的研发速度，由于水平有限， 不提供任何的完整性、可靠性等保证，软件版本更新之后，有些位置名称等内容可能会及时更新，修改方法请参考使用。

一、PWM的应用

1、pwm的添加

增加一路 pwm，以 pwm4 为例说明，其他方法类似，只做为参考。

arch/arm/boot/dts/sun8iw11p1.dtsi

中添加

pwm = &pwm;
pwm0 = &pwm0;
pwm4 = &pwm4;
pwm: pwm@01c23400 {
 	compatible = "allwinner,sunxi-pwm";
	reg = <0x0 0x01c23400 0x0 0x154>;
	pwm-number = <1>;
 	pwm-base = <0x4>;
 	pwms = <&pwm4>;
 };
pwm4: pwm4@01c23400 {
	compatible = "allwinner,sunxi-pwm4";
 	pinctrl-names = "active", "sleep";
 	reg_base = <0x01c23400>;
	reg_peci_offset = <0x00>;
 	reg_peci_shift = <0x04>;
	reg_peci_width = <0x01>;
 	reg_pis_offset = <0x04>;
	reg_pis_shift = <0x04>;
	reg_pis_width = <0x01>;
	reg_crie_offset = <0x10>;
 	reg_crie_shift = <0x08>;
 	reg_crie_width = <0x01>;
	reg_cfie_offset = <0x10>;
 	reg_cfie_shift = <0x09>;
 	reg_cfie_width = <0x01>;
	reg_cris_offset = <0x14>;
	reg_cris_shift = <0x08>;
	reg_cris_width = <0x01>;
 	reg_cfis_offset = <0x14>;
	reg_cfis_shift = <0x09>;
	reg_cfis_width = <0x01>;
	reg_clk_src_offset = <0x28>;
	reg_clk_src_shift = <0x07>;
	reg_clk_src_width = <0x02>;
	reg_bypass_offset = <0x28>;
	reg_bypass_shift = <0x05>;
	reg_bypass_width = <0x01>;
 	reg_clk_gating_offset = <0x28>;
 	reg_clk_gating_shift = <0x04>;
 	reg_clk_gating_width = <0x01>;
 	reg_clk_div_m_offset = <0x28>;
	reg_clk_div_m_shift = <0x00>;
 	reg_clk_div_m_width = <0x04>;
	reg_pdzintv_offset = <0x38>;
 	reg_pdzintv_shift = <0x08>;
	reg_pdzintv_width = <0x08>;
 	reg_dz_en_offset = <0x38>;
	reg_dz_en_shift = <0x00>;
	reg_dz_en_width = <0x01>;
 	reg_enable_offset = <0x40>;
	reg_enable_shift = <0x04>;
	reg_enable_width = <0x01>;
 	reg_cap_en_offset = <0x44>;
 	reg_cap_en_shift = <0x04>;
 	reg_cap_en_width = <0x01>;
 	reg_period_rdy_offset = <0xe0>;
 	reg_period_rdy_shift = <0x0b>;
	reg_period_rdy_width = <0x01>;
	reg_pul_start_offset = <0xe0>;
 	reg_pul_start_shift = <0x0a>;
 	reg_pul_start_width = <0x01>;
 	reg_mode_offset = <0xe0>;
	reg_mode_shift = <0x09>;
 	reg_mode_width = <0x01>;
	reg_act_sta_offset = <0xe0>;
 	reg_act_sta_shift = <0x08>;
	reg_act_sta_width = <0x01>;
 	reg_prescal_offset = <0xe0>;
 	reg_prescal_shift = <0x00>;
 	reg_prescal_width = <0x08>;
	reg_entire_offset = <0xe4>;
	reg_entire_shift = <0x10>;
 	reg_entire_width = <0x10>;
 	reg_active_offset = <0xe4>;
 	reg_active_shift = <0x00>;
 	reg_active_width = <0x10>;
 }

按手册 PWM 修改对应的寄存器。

修改 sys_config.fex 中 twi2_used=0 且增加

[pwm4]
pwm_used = 1
pwm_positive = port:PB20<4><0><default><default>
[pwm4_suspend]
pwm_positive = port:PB20<7><0><default><default>

编译镜像并烧写

2、PWM的测试

echo 0 >/sys/class/pwm/pwmchip4/export
echo 1000000 > /sys/class/pwm/pwmchip4/pwm0/period
echo 500000 > /sys/class/pwm/pwmchip4/pwm0/duty_cycle
echo 1 > /sys/class/pwm/pwmchip4/pwm0/enable

测量得到频率为 1K 方波

echo 0 > /sys/class/pwm/pwmchip4/pwm0/enable
echo 208333> /sys/class/pwm/pwmchip4/pwm0/duty_cycle
echo 416667 > /sys/class/pwm/pwmchip4/pwm0/period
echo 1 > /sys/class/pwm/pwmchip4/pwm0/enable

测量得到频率为 2.4K 方波