digi:arm-embedded:ccmp2:encoder_dts [Digi产品中文Wiki]

这是本文档旧的修订版！

背景：ST的PLC参考设计板对应的设备树源码位于：https://github.com/peyoot/ccmp25_dt/blob/scarthgap/ccmp25-plc.dts ，编码器设备树的部分只是按早期官方文档的一个示例修改，需要进一步修改并验证其可用性。官方文档可能有更新，LPTIM见：https://wiki.st.com/stm32mpu/wiki/LPTIM_device_tree_configuration#On_STM32MP2_series ，而 TIM DEVICE见https://wiki.st.com/stm32mpu/wiki/TIM_device_tree_configuration#On_STM32MP2_series

当前的设计，以counter_DI_1_2为例

&timers1 {
	status = "okay";

	/* USER CODE BEGIN timers1 */
	/delete-property/dmas;
	/delete-property/dma-names;
	/* USER CODE END timers1 */

	
	counter_DI_1_2  {                                          /* remove pwm10,pwm11 and add this */
		pinctrl-names = "default", "sleep";
		pinctrl-0 = <&ccmp25_timers1_ch3_4_pins>;
		pinctrl-1 = <&ccmp25_timers1_ch3_4_sleep_pins>;
		status = "okay";
    };

  
  和
  
 <code>
 ccmp25_timers1_ch3_4_pins: ccmp25-timers1-ch3_4 {
	pins {
		pinmux = <STM32_PINMUX('D',  9,  AF8)>, /* TIM1_CH3_PWM */
		 <STM32_PINMUX('D',  8,  AF8)>; /* TIM1_CH4_PWM */
		bias-disable;
	};
};

ccmp25_timers1_ch3_4_sleep_pins: ccmp25-timers1-ch3_4_sleep {
	pins {
		pinmux = <STM32_PINMUX('D',  9, ANALOG)>, /* TIM1_CH3_PWM */
		 <STM32_PINMUX('D',  8, ANALOG)>; /* TIM1_CH4_PWM */
	};
};
 </code>

注意，上面这个配置并未验证，在AI的协助下，需要的知识点包括：

timers1: timer@address {
    compatible = "st,stm32mp25-timers";
    /* ...其他公共资源... */
    
    pwm { compatible = "st,stm32mp25-pwm"; };   // PWM功能
    timer@0 { compatible = "st,stm32mp25-timer-trigger"; }; // 触发功能
    counter { compatible = "st,stm32mp25-timer-counter"; }; // 编码器/计数器功能
};
// counter子节点专门用于编码器/计数器功能，stm32mp25-timer-counter是STM32MP25系列的新绑定方式，而非以前的stm32-timer-encoder

下面，以这个编码器节点为例，可能需要的改变包括： 1、增加在counter内的compatible说明； 2、counter内增加一些描述

        // 编码器模式参数
        st,counter-mode = "encoder";    // 设置为编码器模式
        st,encoder-mode = <3>;          // 模式3：双通道边沿计数（四倍频），
        st,prescaler = <0>;             // 无预分频
        st,filter = <0>;                // 输入滤波器关闭，这句可先不用，信号抖动可增加滤波器，最大滤波（需根据信号频率调整），如st,filter = <15>

        // 通道映射（CH3和CH4）
        st,channel-config {       //当方向相反时，调整st,encoder-mode或交换CH3/CH4的引脚
            ch3-mode = "input";  // CH3作为编码器输入A
            ch4-mode = "input";  // CH4作为编码器输入B

而pinctrl处也要相应修改一些内容，注意AF8改为AF2，待查文档确认，并在节点名别名处添加encoder以增加识别度，偏置也改为上拉等。

ccmp25_timers1_ch3_4_pins: ccmp25-timers1-ch3_4-encoder {
        pins {
            // PD9: TIM1_CH3, PD8: TIM1_CH4
            pinmux = <STM32_PINMUX('D', 9, AF2)>,  // CH3复用AF2
                     <STM32_PINMUX('D', 8, AF2)>;  // CH4复用AF2
            bias-pull-up;        // 根据编码器类型选择上拉
            drive-push-pull;     // 推挽输出驱动
            slew-rate = <1>;     // 高速模式（>50MHz信号）
        };
};

ccmp25_timers1_ch3_4_sleep_pins: ccmp25-timers1-ch3_4_sleep-encoder {
        pins {
            pinmux = <STM32_PINMUX('D', 9, ANALOG)>,  // 睡眠时设为模拟
                     <STM32_PINMUX('D', 8, ANALOG)>;
        };
};

下面讲解如何确认I/O pin alternate-function multiplexer and mapping，在处理器的文档RM0457 Rev 5中，page1368开始为GPIO相关文档，page1370处说到： Each I/O pin has a multiplexer with up to 16 alternate function inputs (AF0 to AF15), that can be configured through GPIOx_AFRL (for pin 0 to 7) and GPIOx_AFRH (for pin 8 to 15):

对应到这里引脚为8,9，则是看GPIOx_AFRH，在page1385处为GPIOx_AFRL，在page1386处为GPIOx_AFRH。

*疑点** 在文档的timers中，即64,65章节，pins and internal signals表格里描述到：即

Each channel can be used for capture,
compare or PWM.
TIM_CH1 and TIM_CH2 can also be used
as external clock (below 1/4 of the
tim_ker_ck clock), external trigger and
quadrature encoder inputs.
TIM_CH1, TIM_CH2 and TIM_CH3 can be
used to interface with digital hall effect
sensors

也就是，定时器如果是作为capture,compare或PWM，随便用一个通道即可，但如果要用作quadrature encoder inputs，则需要用CH1和CH2，而PLC开发板的设计文件中，大部是用CH3和CH4，需原厂确认是否有问题

假定CH3,CH4也可用作编码器接口，我目录改了一下：

/*  encoder interface for DI1 and DI2 */
counter_DI_1_2  {                                          
		compatible = "st,stm32mp25-timer-counter";
		pinctrl-names = "default", "sleep";
		pinctrl-0 = <&ccmp25_timers1_ch3_4_pins>;
		pinctrl-1 = <&ccmp25_timers1_ch3_4_sleep_pins>;
		status = "okay";
		st,counter-mode = "encoder";
        st,encoder-mode = <3>;
        st,prescaler = <0>;
        st,channel-config {
            ch3-mode = "input";
            ch4-mode = "input";
		};
    
    };



	ccmp25_timers1_ch3_4_pins: ccmp25-timers1-ch3_4-encoder {
		pins {
			pinmux = <STM32_PINMUX('D',  9,  AF2)>, /* TIM1_CH3_PWM */
			 <STM32_PINMUX('D',  8,  AF2)>; /* TIM1_CH4_PWM */
			bias-pull-up;
            drive-push-pull;
            slew-rate = <1>;
		};
	};

ccmp25_timers1_ch3_4_sleep_pins: ccmp25-timers1-ch3_4_sleep-encoder {
		pins {
			pinmux = <STM32_PINMUX('D',  9, ANALOG)>, /* TIM1_CH3_PWM */
			 <STM32_PINMUX('D',  8, ANALOG)>; /* TIM1_CH4_PWM */
		};
	};

用户空间的验证如下：

# 启用计数器
echo 1 > /sys/bus/counter/devices/counter0/enable

# 读取当前计数值
cat /sys/bus/counter/devices/counter0/count

# 旋转编码器后，观察数值变化

编码器DTS探究