OpenWRT(九)DTS及串口

一、DTS

DTS是Device Tree Source的缩写，它用来描述设备的硬件细节。说简单点就是开发板的配置文件。

二、分析OpenWRT的dts文件

以rt5350.dtsi作为分析

//DTS格式有点类似Json

/ {                             // "/"表示root节点
  //#address-cells和#size-cells分别决定reg属性的address和length字段的长度。比如reg<0x500 0x100>,0x500和0x100两个数值都是32位的
  #address-cells = <1>;         //地址长度为1个32位的整型
  #size-cells = <1>;            //length为1个32位的整型
  //ralink:厂商  rt5350-soc:具体的芯片型号
  compatible = "ralink,rt5350-soc";  //定义系统名称，compatible属性用于驱动和设备的绑定，属性值形式：<manufacturer>,<model>

  cpus {   //芯片中的所有cpu定义
    cpu@0 {    //cpu@0表示第一个cpu,如果还有其他cpu就依次定义为cpu@1 cpu@2 .....
      compatible = "mips,mips24KEc";   //mips的cpu内核，mips24KEc是具体型号
    };
  };

  chosen {
    bootargs = "console=ttyS0,57600"; //启动参数，定义了串口ttyS0为调试串口，波特率为57600
  };

  cpuintc: cpuintc@0 {
    #address-cells = <0>;
    #interrupt-cells = <1>;   //中断号长度
    interrupt-controller;
    compatible = "mti,cpu-interrupt-controller";
  };

  aliases {         //定义别名
    spi0 = &spi0;
    spi1 = &spi1;
    serial0 = &uartlite;   //uartlite的别名为serial0
  };

  palmbus@10000000 {  // @后面代表address
    compatible = "palmbus";
    reg = <0x10000000 0x200000>;         //address: 0x10000000   length:0x200000
    ranges = <0x0 0x10000000 0x1FFFFF>;  //地址转换表 ：<子地址 父地址 子地址空间的映射大小>

    #address-cells = <1>;     //决定子节点reg的address字段长度
    #size-cells = <1>;        //决定子节点reg的length字段长度

    sysc@0 {
      compatible = "ralink,rt5350-sysc", "ralink,rt3050-sysc";   //兼容rt5350和rt3050
      reg = <0x0 0x100>;
    };

    timer@100 {
      compatible = "ralink,rt5350-timer", "ralink,rt2880-timer";
      reg = <0x100 0x20>;
      //在RT5350中，将GPIO设置为中断方式，当它触发中断时，CPU的中断控制器先获取中断，在这里叫一级中断。
      //判断它是GPIO中断，然后进入GPIO中断控制器判断是哪个GPIO产生的中断，这里叫二级中断，再进行中断处理。
      interrupt-parent = <&intc>;    //当上级发生intc中断时才来查询是否是该中断。
      interrupts = <1>;        //中断等级
    };

    watchdog@120 {
      compatible = "ralink,rt5350-wdt", "ralink,rt2880-wdt";
      reg = <0x120 0x10>;

      resets = <&rstctrl 8>;
      reset-names = "wdt";

      interrupt-parent = <&intc>;
      interrupts = <1>;
    };

    intc: intc@200 {
      compatible = "ralink,rt5350-intc", "ralink,rt2880-intc";
      reg = <0x200 0x100>;

      resets = <&rstctrl 19>;
      reset-names = "intc";

      interrupt-controller;
      #interrupt-cells = <1>;

      interrupt-parent = <&cpuintc>;
      interrupts = <2>;
    };

    memc@300 {
      compatible = "ralink,rt5350-memc", "ralink,rt3050-memc";
      reg = <0x300 0x100>;

      resets = <&rstctrl 20>;
      reset-names = "mc";

      interrupt-parent = <&intc>;
      interrupts = <3>;
    };

    uart@500 {
      compatible = "ralink,rt5350-uart", "ralink,rt2880-uart", "ns16550a";
      reg = <0x500 0x100>;

      resets = <&rstctrl 12>;
      reset-names = "uart";

      interrupt-parent = <&intc>;
      interrupts = <5>;

      reg-shift = <2>;

      status = "disabled";
    };

    gpio0: gpio@600 {
      compatible = "ralink,rt5350-gpio", "ralink,rt2880-gpio";
      reg = <0x600 0x34>;

      resets = <&rstctrl 13>;
      reset-names = "pio";

      interrupt-parent = <&intc>;
      interrupts = <6>;

      gpio-controller;
      #gpio-cells = <2>;

      ralink,gpio-base = <0>;
      ralink,num-gpios = <22>;
      ralink,register-map = [ 00 04 08 0c
            20 24 28 2c
            30 34 ];
    };

    gpio1: gpio@660 {
      compatible = "ralink,rt5350-gpio", "ralink,rt2880-gpio";
      reg = <0x660 0x24>;

      interrupt-parent = <&intc>;
      interrupts = <6>;

      gpio-controller;
      #gpio-cells = <2>;

      ralink,gpio-base = <22>;
      ralink,num-gpios = <6>;
      ralink,register-map = [ 00 04 08 0c
            10 14 18 1c
            20 24 ];

      status = "disabled";     //本模块状态
    };

    i2c@900 {
      compatible = "link,rt5350-i2c", "ralink,rt2880-i2c";
      reg = <0x900 0x100>;

      resets = <&rstctrl 16>;
      reset-names = "i2c";

      #address-cells = <1>;
      #size-cells = <0>;

      pinctrl-names = "default";
      pinctrl-0 = <&i2c_pins>;

      status = "disabled";
    };

    spi0: spi@b00 {
      compatible = "ralink,rt5350-spi", "ralink,rt2880-spi";
      reg = <0xb00 0x40>;

      resets = <&rstctrl 18>;
      reset-names = "spi";

      #address-cells = <1>;
      #size-cells = <1>;

      pinctrl-names = "default";
      pinctrl-0 = <&spi_pins>;

      status = "disabled";
    };

    spi1: spi@b40 {
      compatible = "ralink,rt5350-spi", "ralink,rt2880-spi";
      reg = <0xb40 0x60>;

      resets = <&rstctrl 18>;
      reset-names = "spi";

      #address-cells = <1>;
      #size-cells = <0>;

      pinctrl-names = "default";
      pinctrl-0 = <&spi_cs1>;

      status = "disabled";
    };

    uartlite: uartlite@c00 {
      compatible = "ralink,rt5350-uart", "ralink,rt2880-uart", "ns16550a";
      reg = <0xc00 0x100>;

      resets = <&rstctrl 19>;
      reset-names = "uartl";

      interrupt-parent = <&intc>;
      interrupts = <12>;

      pinctrl-names = "default";
      pinctrl-0 = <&uartlite_pins>;

      reg-shift = <2>;
    };

    systick@d00 {
      compatible = "ralink,rt5350-systick", "ralink,cevt-systick";
      reg = <0xd00 0x10>;

      interrupt-parent = <&cpuintc>;
      interrupts = <7>;
    };
  };

  pinctrl {  //引脚控制
    compatible = "ralink,rt2880-pinmux";

    pinctrl-names = "default";
    pinctrl-0 = <&state_default>;

    state_default: pinctrl0 {
    };

    spi_pins: spi {
      spi {
        ralink,group = "spi";
        ralink,function = "spi";
      };
    };

    i2c_pins: i2c {
      i2c {
        ralink,group = "i2c";
        ralink,function = "i2c";
      };
    };

    phy_led_pins: phy_led {
      phy_led {
        ralink,group = "led";
        ralink,function = "led";
      };
    };

    uartlite_pins: uartlite {
      uart {
        ralink,group = "uartlite";
        ralink,function = "uartlite";
      };
    };

    uartf_pins: uartf {
      uartf {
        ralink,group = "uartf";
        ralink,function = "uartf";
      };
    };

    spi_cs1: spi1 {
      spi1 {
        ralink,group = "spi_cs1";
        ralink,function = "spi_cs1";
      };
    };
  };

  rstctrl: rstctrl {
    compatible = "ralink,rt5350-reset", "ralink,rt2880-reset";
    #reset-cells = <1>;
  };

  usbphy: usbphy {
    compatible = "ralink,rt3352-usbphy";
    #phy-cells = <1>;

    resets = <&rstctrl 22 &rstctrl 25>;
    reset-names = "host", "device";
  };

  ethernet@10100000 {
    compatible = "ralink,rt5350-eth";
    reg = <0x10100000 0x10000>;

    resets = <&rstctrl 21 &rstctrl 23>;
    reset-names = "fe", "esw";

    interrupt-parent = <&cpuintc>;
    interrupts = <5>;

    mediatek,switch = <&esw>;
  };

  esw: esw@10110000 {
    compatible = "ralink,rt3050-esw";
    reg = <0x10110000 0x8000>;

    resets = <&rstctrl 23>;
    reset-names = "esw";

    interrupt-parent = <&intc>;
    interrupts = <17>;
  };

  wmac@10180000 {
    compatible = "ralink,rt5350-wmac", "ralink,rt2880-wmac";
    reg = <0x10180000 0x40000>;

    interrupt-parent = <&cpuintc>;
    interrupts = <6>;

    ralink,eeprom = "soc_wmac.eeprom";
  };

  ehci@101c0000 {
    compatible = "generic-ehci";
    reg = <0x101c0000 0x1000>;

    phys = <&usbphy 1>;
    phy-names = "usb";

    interrupt-parent = <&intc>;
    interrupts = <18>;
  };

  ohci@101c1000 {
    compatible = "generic-ohci";
    reg = <0x101c1000 0x1000>;

    phys = <&usbphy 1>;
    phy-names = "usb";

    interrupt-parent = <&intc>;
    interrupts = <18>;
  };
};

三、OpenWRT串口的使用

以RT5350进行举例：

1、进入openwrt/target/linux/ramips/dts目录，打开rt5350.dtsi,即上面的文件。找到下面的内容：

将红色框框的内容去掉就使能了串口。

2、因为uart的配置在uartlite（调试串口）前面，所以uart会被初始化为ttyS0,而ttyS0之前却被配置为调试串口。

为了解决这个问题，我们将uart的配置放到uartlite后面就可以了！

3、串口引脚之前被配置为普通IO口，所以为了防止干扰需要把IO口中的配置去掉。打开openwrt/target/linux/ramips/dts/MPRA2.dts,找到下面内容

把红色框框的内容去掉。

4、重新编译就OK了！ 将编译好的固件下载到开发板后启动系统后，在/dev/目录下会多出ttyS1这个设备。这个就是我们添加的串口设备。