Device Tree Overlay

 Terminology

• dts  Device tree source file

• dtc  Device tree compiler

• dtb  device tree blob

• Bunch of dtb binaries are in /boot folder.

• Overlay: allows user to be modify pin muxing.

• Cape manager: load & unload overlays.

• Slots : are its interface

• Default overlay:

1. Onboard storage

2. HDMI

• There are free slots for 4 physical capes.

• To see the list of loaded slots, you can do the following

1. export SLOTS =/sys/devices/bone_capemgr.9/slots

1. where 9  varies depending on the device

2. echo $SLOTS

• In order to add the slot during boot itself, add the line to uEnv.txt

1. capemgr.enable_partno=BB_ADC

Compiling Overlay

• To build the dts file to dtb, use the following syntax

1. dtc -O dtb -o enable-uart5-00A0.dtbo -b 0 -@ enable-uart5.dts

• where

1. –O  dtb is the output format

2. –o  output filename

3. –b  0 setting the physical boot cpu ( a zero)

4. -@  generates symbol node as part of dynamic DT loading of overlay