Ping :) On Sun, Aug 4, 2019 at 2:01 AM Vijay Kumar Banerjee < vijaykumar9...@gmail.com> wrote:
> --- > user/bsps/arm/beagle.rst | 21 +-------- > user/exe/device-tree.rst | 92 ++++++++++++++++++++++++++++++++++++++++ > user/exe/index.rst | 1 + > 3 files changed, 95 insertions(+), 19 deletions(-) > create mode 100644 user/exe/device-tree.rst > > diff --git a/user/bsps/arm/beagle.rst b/user/bsps/arm/beagle.rst > index eb4ecfb..fa7fa05 100644 > --- a/user/bsps/arm/beagle.rst > +++ b/user/bsps/arm/beagle.rst > @@ -40,25 +40,8 @@ from the libbsd HEAD of freebsd-org. For example if the > HEAD is at > Then the right Device Tree Source (DTS) file is: > > https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/gnu/dts/arm/am335x-boneblack.dts > > -.. code-block:: shell > - :linenos: > - > - #building the dtb > - #We will use the script from > https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/tools/fdt/make_dtb.sh > - > - #The make_dtb.sh script uses environment variable MACHINE > - export MACHINE='arm' > - > - SCRIPT_DIR=$HOME/freebsd/sys/tools/fdt > - > - #The arguments to the script are > - # $1 -> Build Tree > - # $2 -> DTS source file > - # $3 -> output path of the DTB file > - > - ${SCRIPT_DIR}/make_dtb.sh ${SCRIPT_DIR}/../../ \ > - ${SCRIPT_DIR}/../../gnu/dts/arm/am335x-boneblack.dts \ > - $(pwd) > +Please refer to the :ref:`device-tree` to know more about building and > applying > +the Device Trees. > > Writing the uEnv.txt file > ------------------------- > diff --git a/user/exe/device-tree.rst b/user/exe/device-tree.rst > new file mode 100644 > index 0000000..bd21552 > --- /dev/null > +++ b/user/exe/device-tree.rst > @@ -0,0 +1,92 @@ > +.. SPDX-License-Identifier: CC-BY-SA-4.0 > + > +.. Copyright (C) 2019 Vijay Kumar Banerjee <vijaykumar9...@gmail.com> > + > +Device Tree > +=========== > +.. index:: Device Tree > + > +A Device Tree is a data structure that is used to describe properties of > +non-discoverable hardware instead of hardcoding them in the kernel. The > device > +tree data is generally stored in a `.dts` or a Device Tree Source (DTS) > file. > +This file is then compiled into a binary format called Device Tree Blob > (DTB) > +with `.dtb` extension. RTEMS preferably uses a DTB built from the FreeBSD > source > +tree matching the freebsd-org HEAD commit hash in libBSD. > + > +Building the DTB > +---------------- > + > +A single DTB file can be built using the `dtc` tool in libfdt using the > +following command: > + > +.. code-block:: none > + > + dtc -@ -I dts -O dtb -o my-devicetree.dtb my-devicetree.dts > + > +For building the DTB from the FreeBSD source, the `make_dtb.sh` script > +from `freebsd/sys/tools/fdt` must be used as most of the DTS files in > FreeBSD > +have included `.dtsi` files from their source tree. An example is given > below as > +a reference for how to build the device tree from the FreeBSD source. > + > +`NOTE: The following example uses FreeBSD master branch from github > mirror as > +an example. It is advised to always use the source from the commit > matching the > +freebsd-org HEAD in libBSD.` > + > +.. code-block:: shell > + :linenos: > + > + #We're using the script from freebsd/sys/tools/make_dtb.sh > + #Target device: Beaglebone Black. > + #Architecture: Arm. > + #DTS source name: am335x-boneblack.dts > + > + #The make_dtb.sh script uses environment variable MACHINE > + export MACHINE='arm' > + > + SCRIPT_DIR=$HOME/freebsd/sys/tools/fdt > + > + #The arguments to the script are > + # $1 -> Build Tree (This is the path to freebsd/sys/ directory) > + # $2 -> DTS source file > + # $3 -> output path of the DTB file > + > + ${SCRIPT_DIR}/make_dtb.sh ${SCRIPT_DIR}/../../ \ > + ${SCRIPT_DIR}/../../gnu/dts/arm/am335x-boneblack.dts \ > + $(pwd) > + > +Using Device Tree Overlay > +------------------------- > + > +Device tree overlay is used either to add properties or devices to the > existing > +device tree. Adding any property to DTS using an overlay will override the > +current values in the DTB. The Overlays enable us to modify the device > tree > +using a small maintainable plugin without having to edit the whole Base > Tree. > + > +There are two ways of applying an overlay on top of the built DTB. > + > +#. Use fdtoverlay from libfdt > + > +#. Add the overlay in the root partition of the SD card and apply it > using U-Boot > + > +The fdtoverlay command can be used as follows: > + > +.. code-block:: none > + > + fdtoverlay -i my-base-tree.dtb -o output-tree.dtb my-overlay.dtbo > + > +To apply it from U-Boot during system initialization we have to add the > device > +tree overlay file in the root directory of the SD card and use U-Boot > commands > +to apply the overlay. > + > +Below is given the series of U-Boot commands that can be used to apply the > +overlay, given that the overlay blob (.dtbo) file is already in the card. > + > +.. code-block:: shell > + > + fatload mmc 0:1 0x80800000 rtems-app.img > + fatload mmc 0:1 0x88000000 my-base-tree.dtb > + fdt addr 0x88000000 > + fatload mmc 0:1 0x88100000 my-overlay.dtbo > + fdt resize 0x1000 > + fdt apply 0x88100000 > + bootm 0x80800000-0x88000000 > diff --git a/user/exe/index.rst b/user/exe/index.rst > index 3e9b571..e22420a 100644 > --- a/user/exe/index.rst > +++ b/user/exe/index.rst > @@ -21,3 +21,4 @@ execiutable, and creating and dynamically loading code. > initialization > debugging > loader > + device-tree > -- > 2.20.1 > >
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