原文地址：http://blog.chinaunix.net/uid-29616823-id-4390033.html

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接上xx路由器的串列埠後有輸出但無法輸入，用示波器量下訊號-----可能是uboot裡面把RX引腳給配置了。

1.屬性的定義採用property ＝ value的形式，“”字串、<>32或64位值、[]二進位制[0x01 0x02]
2.用=賦值的才是節點屬性，其他是子節點。
3.root節點的compitable屬性供核心選擇匹配機器碼machinetype，其他節點的compitable屬性供核心選擇匹配對應的驅動
（如三星2416的lcd控制器節點，核心裡面lcd的驅動有很多）
4.DTB檔案頭boot_paras_header,其中的magic欄位用來標誌Uboot傳來的啟動引數是DTB還是taglist(bootargs)
，xx_offset標誌DTB在記憶體中的地址。
compatible：相容的，相容的


/ {---------------------"/"表示根節點的名稱，一個裝置樹只能有一個根節點多個檔案中的根節點在編譯時會被合併。
#address-cells = <1>;---------------表示地址空間的個數，如系統有兩片記憶體，那就需要<a b c d>兩組資料來表示，ab表示記憶體1的空間 cd表示記憶體2空間。
#size-cells = <1>;------------------表示地址空間所需位元組數，如表示64位的GPIO控制暫存器組就需要<0x00000001 0x000000002 0x00000001 0x000000006

>
表示的空間是0x00000001000000002到00000001000000006
compatible = "ralink,mtk7620a-soc";----“compatible”屬性表示CPU所述系列，如mips架構ralink，mtk7620a系列
、arm架構stm32，cortex-M3系列。

cpus {
[email protected] {---------節點名稱@節點暫存器偏移地址或節點裝置編號，若該節點無reg屬性則不寫定義成空節點即可。
compatible = "mips,mips24KEc";
};
};


chosen {
bootargs = "console=ttyS0,57600";-----通過dts給核心傳遞uboot的bootargs引數，uboot省事了
};


cpuintc:

[email protected] {-------------該節點名稱是中斷控制器，cpuintc是標籤即[email protected]，
為了方便引用[email protected]。
#address-cells = <0>;
#interrupt-cells = <1>;
interrupt-controller;
compatible = "mti,cpu-interrupt-controller";
};


[email protected] {------palmbus類似arm的AMBA，屬於片內匯流排。
compatible = "palmbus";
reg = <0x10000000 0x200000>;---reg屬性表示該控制器的reg地址及總長度
                ranges = <0x0 0x10000000 0x1FFFFF>;


#address-cells = <1>;----若節點的子節點有控制暫存器，則必須定義這兩個屬性。
#size-cells = <1>;

[email protected] {
compatible = "ralink,mt7620a-sysc", "ralink,rt3050-sysc";
reg = <0x0 0x100>;
};


[email protected] {
compatible = "ralink,mt7620a-timer", "ralink,rt2880-timer";
reg = <0x100 0x20>;


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


[email protected] {
compatible = "ralink,mt7620a-wdt", "ralink,rt2880-wdt";
reg = <0x120 0x10>;


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


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


intc: [email protected] {-----intc為標籤（為方便被其他節點引用）
compatible = "ralink,mt7620a-intc", "ralink,rt2880-intc";
reg = <0x200 0x100>;


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


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


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


[email protected] {----------描述系統記憶體的節點，為根節點的子節點
compatible = "ralink,mt7620a-memc", "ralink,rt3050-memc";
reg = <0x300 0x100>;


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


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


gpio0: [email protected] {
compatible = "ralink,mt7620a-gpio", "ralink,rt2880-gpio";
reg = <0x600 0x34>;


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


interrupt-parent = <&intc>;
interrupts = <6>;---------表示其在中斷控制器中的硬體中斷編號，分系統異常中斷/systick中斷/兩個外部中斷。。。等


gpio-controller;
#gpio-cells = <2>;-----表示gpio控制暫存器是64位的


ralink,gpio-base = <0>;----該組gpio從GPIO0開始
ralink,num-gpios = <24>;-------到GPIO24結束
ralink,register-map = [ 00 04 08 0c
20 24 28 2c
30 34 ];
};


gpio1: [email protected] {
compatible = "ralink,mt7620a-gpio", "ralink,rt2880-gpio";
reg = <0x638 0x24>;


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


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


ralink,gpio-base = <24>;
ralink,num-gpios = <16>;
ralink,register-map = [ 00 04 08 0c
10 14 18 1c
20 24 ];-----執行cat /proc/iomem顯示的數值？


status = "disabled";
};


gpio2: [email protected] {
compatible = "ralink,mt7620a-gpio", "ralink,rt2880-gpio";
reg = <0x660 0x24>;


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


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


ralink,gpio-base = <40>;
ralink,num-gpios = <32>;
ralink,register-map = [ 00 04 08 0c
10 14 18 1c
20 24 ];


status = "disabled";
};


gpio3: [email protected] {
compatible = "ralink,mt7620a-gpio", "ralink,rt2880-gpio";
reg = <0x688 0x24>;


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


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


ralink,gpio-base = <72>;
ralink,num-gpios = <1>;
ralink,register-map = [ 00 04 08 0c
10 14 18 1c
20 24 ];


status = "disabled";
};


[email protected] {
compatible = "link,mt7620a-i2c", "ralink,rt2880-i2c";
reg = <0x900 0x100>;


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


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


status = "disabled";


pinctrl-names = "default";----i2c除了對i2c控制器暫存器定義外，還要對i2c所用的gpio管腳定義
pinctrl-0 = <&i2c_pins>;
};


[email protected] {
compatible = "ralink,mt7620a-i2s";
reg = <0xa00 0x100>;


resets = <&rstctrl 17>;
reset-names = "i2s";


interrupt-parent = <&intc>;
interrupts = <10>;


dmas = <&gdma 4>,
<&gdma 5>;
dma-names = "tx", "rx";


status = "disabled";
};


[email protected] {
compatible = "ralink,mt7620a-spi", "ralink,rt2880-spi";
reg = <0xb00 0x100>;


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


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


status = "disabled";


pinctrl-names = "default";
pinctrl-0 = <&spi_pins>;-----spi_pins不在dts檔案中定義？
};


[email protected] {
compatible = "ralink,mt7620a-uart", "ralink,rt2880-uart", "ns16550a";
reg = <0xc00 0x100>;


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


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


reg-shift = <2>;


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


[email protected] {
compatible = "ralink,mt7620a-uart", "ralink,rt2880-uart", "ns16550a";
reg = <0x500 0x100>;


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


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


reg-shift = <2>;


pinctrl-names = "default";
pinctrl-0 = <&pcm_uartf_pins>;
};


[email protected] {
compatible = "ralink,mt7620a-systick", "ralink,cevt-systick";
reg = <0xd00 0x10>;


resets = <&rstctrl 28>;
reset-names = "intc";


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


[email protected] {
compatible = "ralink,mt7620a-pcm";
reg = <0x2000 0x800>;


resets = <&rstctrl 11>;--------resets屬性含義？
reset-names = "pcm";


interrupt-parent = <&intc>;
interrupts = <4>;


status = "disabled";
};


gdma: [email protected] {
compatible = "ralink,mt7620a-gdma", "ralink,rt2880-gdma";
reg = <0x2800 0x800>;


resets = <&rstctrl 14>;
reset-names = "dma";


interrupt-parent = <&intc>;
interrupts = <7>;


#dma-cells = <1>;
#dma-channels = <16>;
#dma-requests = <16>;


status = "disabled";
};
};


pinctrl {
compatible = "ralink,rt2880-pinmux";
pinctrl-names = "default";
pinctrl-0 = <&state_default>;
state_default: pinctrl0 {
};
pcm_uartf_pins: pcm_uartf {
pcm_uartf {
ralink,group = "uartf";
ralink,function = "pcm uartf";
};
};
spi_pins: spi {
spi {
ralink,group = "spi";
ralink,function = "spi";
};
};
i2c_pins: i2c {
i2c {
lantiq,group = "i2c";
lantiq,function = "i2c";
};
};
uartlite_pins: uartlite {
uart {
ralink,group = "uartlite";
ralink,function = "uartlite";
};
};
mdio_pins: mdio {
mdio {
ralink,group = "mdio";
ralink,function = "mdio";
};
};
ephy_pins: ephy {
ephy {
ralink,group = "ephy";
ralink,function = "ephy";
};
};
wled_pins: wled {
wled {
ralink,group = "wled";
ralink,function = "wled";
};
};
rgmii1_pins: rgmii1 {
rgmii1 {
ralink,group = "rgmii1";
ralink,function = "rgmii1";
};
};
rgmii2_pins: rgmii2 {
rgmii2 {
ralink,group = "rgmii2";
ralink,function = "rgmii2";
};
};
};


rstctrl: rstctrl {
compatible = "ralink,mt7620a-reset", "ralink,rt2880-reset";
#reset-cells = <1>;
};


ubsphy {
compatible = "ralink,mt7620a-usbphy";


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


[email protected] {
compatible = "ralink,mt7620a-eth";
reg = <0x10100000 10000>;


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


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


resets = <&rstctrl 21 &rstctrl 23>;----當<>內出現多個數據時，一般兩個資料一組。。。
reset-names = "fe", "esw";


[email protected] {
compatible = "ralink,mt7620a-gsw-port", "ralink,eth-port";
reg = <4>;


status = "disabled";
};


[email protected] {
compatible = "ralink,mt7620a-gsw-port", "ralink,eth-port";
reg = <5>;


status = "disabled";
};


mdio-bus {
#address-cells = <1>;
#size-cells = <0>;


status = "disabled";
};
};


[email protected] {
compatible = "ralink,mt7620a-gsw";
reg = <0x10110000 8000>;


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


[email protected] {
compatible = "ralink,mt7620a-sdhci";
reg = <0x10130000 4000>;


interrupt-parent = <&intc>;
interrupts = <14>;


status = "disabled";
};


[email protected] {
compatible = "ralink,rt3xxx-ehci";
reg = <0x101c0000 0x1000>;


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


status = "disabled";
};


[email protected] {
compatible = "ralink,rt3xxx-ohci";
reg = <0x101c1000 0x1000>;


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


status = "disabled";
};


[email protected] {
compatible = "ralink,mt7620a-pci";
reg = <0x10140000 0x100
0x10142000 0x100>;


resets = <&rstctrl 26>;
reset-names = "pcie0";


interrupt-parent = <&cpuintc>;
interrupts = <4>;


status = "disabled";
};
};
==============================================================================
例如一個在.dts檔案中關於gpio資源的描述：
  gpio: [email protected] {
            #gpio-cells = <2>;
            compatible = "cavium,octeon-3860-gpio";
            reg = <0x10700 0x00000800 0x0 0x100>;


            gpio-controller;
........
根據其描述， 可知道gpio控制器的IO記憶體起始地址為：0x107900000800， 長度為0x100.
即從 0x107900000800 到 0x1079000008ff.
在目標板裡使用  cat /proc/iomem  可以看到：
1070000000800-10700000008ff : /[email protected]/[email protected]

====================================================================================
/dts-v1/;


/include/ "xxe.dtsi"


/ {
compatible = "xxx0", "ralink,mt7620a-soc";
model = "xxxxx";------model屬性表示my board name。


[email protected] {
gpio1: [email protected] {
status = "okay";
};


gpio2: [email protected] {
status = "okay";
};


[email protected] {
status = "okay";


[email protected] {
#address-cells = <1>;
#size-cells = <1>;
compatible = "en25q64";
reg = <0 0>;
linux,modalias = "m25p80", "w25p128";
spi-max-frequency = <10000000>;


[email protected] {[email protected]後面為該節點暫存器的偏移地址或裝置編號
label = "u-boot";
reg = <0x0 0x30000>;---reg屬性表示暫存器偏移地址和長度，
還能表示flash分割槽的便宜地址和長度
read-only;
};


[email protected] {
label = "u-boot-env";
reg = <0x30000 0x10000>;
read-only;
};


factory: [email protected] {
label = "factory";
reg = <0x40000 0x10000>;
};


[email protected] {
label = "firmware";
reg = <0x50000 0xfb0000>;
};
};
};
};


pinctrl {
state_default: pinctrl0 {
default {
ralink,group = "i2c", "rgmii1", "rgmii2";
ralink,function = "gpio";
};
};
};


[email protected] {
mtd-mac-address = <&factory 0x28>;
ralink,port-map = "llllw";
};


[email protected] {
ralink,port4 = "ephy";
};


[email protected] {
status = "okay";
};


[email protected] {
status = "okay";
};


gpio-leds {
compatible = "gpio-leds";


sys {
label = "xxx:blue:sys";
gpios = <&gpio2 20 1>;---用gpio2組的GPIO管腳，偏移地址是20即該組的第20個管腳，預設輸出高電平。
}; 


wan {
label = "xxx:blue:wan";
gpios = <&gpio2 24 1>;
};


wireless {
label = "xxx:blue:wireless";
gpios = <&gpio2 21 1>;
};
};


gpio-keys-polled {
compatible = "gpio-keys-polled";
#address-cells = <1>;
#size-cells = <0>;
poll-interval = <20>;


zigbee {
label = "zigbee";
gpios = <&gpio2 23 1>;-------按此按鍵後開啟zigbee模組業務？
linux,code = <0x197>;
};
reset {
label = "reset";
gpios = <&gpio2 22 1>;
linux,code = <0x198>;-------該屬性的含義？
}; 
};


i2c-gpio {
compatible = "i2c-gpio";
gpios = <&gpio0 1 0 &gpio0 2 0>;-------i2c匯流排配置兩個GPIO管腳
i2c-gpio,delay-us = <100>; /*10KHz */
#address-cells = <1>;
#size-cells = <0>;

[email protected] {-----------------pcf8563為掛在該i2c匯流排的rtc晶片型號
compatible = "nxp,pcf8563";
reg = <0x51>;
}; 
};
};