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 = 1pwm_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/exportecho 1000000 > /sys/class/pwm/pwmchip4/pwm0/periodecho 500000 > /sys/class/pwm/pwmchip4/pwm0/duty_cycleecho 1 > /sys/class/pwm/pwmchip4/pwm0/enable
测量得到频率为 1K 方波
echo 0 > /sys/class/pwm/pwmchip4/pwm0/enableecho 208333> /sys/class/pwm/pwmchip4/pwm0/duty_cycleecho 416667 > /sys/class/pwm/pwmchip4/pwm0/periodecho 1 > /sys/class/pwm/pwmchip4/pwm0/enable
测量得到频率为 2.4K 方波
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