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{{template>intern:templates:tabs_bootstrap_new|lang="intern"|mod_name="tqma7x"|mod_name_head="TQMa7x"|mod_arch="arm"|bsp_name="linux"|bsp_name_head="Linux"|build_system="ptxdist"|build_system_head="PTXdist"}}
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===== How-to =====
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===== Load / Change / Save the Device Tree under U-Boot =====
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Devicetree can be edit with the **fdt** commands under U-Boot.

<WRAP round important 60%>For testing purpose only. For bigger changes, please compile the Devicetree.\\   Therefore you can have a look at the following [[intern:general_information:tutorial:devicetree|tutorial]].</WRAP>
<WRAP round info 60%>
Tested with **TQMa7x BSP Rev.0101**
</WRAP>


1) At first the fdt file has to be loaded from the current boot medium (mmc) into RAM.
<code>=> run loadfdt</code>

2) Next step is to set the predefined U-Boot environment variable fdt_addr through the **fdt addr** command. 
<code>=> fdt addr $fdt_addr</code>

3) Afterwards the size of the fdt has to be increased (to the next 4K divider) in order to have some space for modifications. This is simply done by entering: 
<code>=> fdt resize </code> 

4) List device in the tree you want to change to have a look at the default settings.
++++Example|
<code>
=> fdt list /gpio-leds
gpio-leds {
        compatible = "gpio-leds";
        status = "okay";
        led1 {
        };
        led2 {
        };
};
=> fdt print /gpio-leds
gpio-leds {
        compatible = "gpio-leds";
        status = "okay";
        led1 {
                label = "led1";
                gpios = <0x0000005f 0x00000008 0x00000000>;
                linux,default-trigger = "default-on";
        };
        led2 {
                label = "led2";
                gpios = <0x0000005f 0x00000009 0x00000000>;
                linux,default-trigger = "heartbeat";
        };
};
</code>
++++

5) To modify a value of a propertie use the **fdt set** command.
<code>=> fdt set <path> <property> <value> </code>
++++Example|
<code>=> fdt set /gpio-leds status disabled </code>
++++

6) //Optional:// If you want to save your modified Devicetree back to mmc you'll have to run the following command:

<code>=> fatwrite mmc $mmcdev:$firmwarepart $fdt_addr $fdt_file <totalsize></code>
<wrap tip>You can find out <totalsize> of the modified fdt by entering the command **fdt header**</wrap>

Otherwise you can boot your module with the changed Devicetree right after the modification.
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