On Sat, Jul 27, 2019 at 5:49 PM Christian Mauderer <l...@c-mauderer.de> wrote:
> Hello Vijay, > > sorry for the long delay between posting and review. It was a busy week. > > Would that replace part of the documentation you did in the beagle BSP? > In that case it might could be good to remove it from there and put up a > reference. > > @all: Could one of our native English speakers please proof-read that too? > > Hi, I have posted the v3 of the patch with the corrections you noted, please have a look: https://lists.rtems.org/pipermail/devel/2019-July/026943.html > On 23/07/2019 06:41, Vijay Kumar Banerjee wrote: > > --- > > user/exe/device-tree.rst | 100 +++++++++++++++++++++++++++++++++++++++ > > user/exe/index.rst | 1 + > > 2 files changed, 101 insertions(+) > > create mode 100644 user/exe/device-tree.rst > > > > diff --git a/user/exe/device-tree.rst b/user/exe/device-tree.rst > > new file mode 100644 > > index 0000000..fcbcfd7 > > --- /dev/null > > +++ b/user/exe/device-tree.rst > > @@ -0,0 +1,100 @@ > > +.. SPDX-License-Identifier: CC-BY-SA-4.0 > > + > > +.. Copyright (C) 2018 Vijay Kumar Banerjee <vijaykumar9...@gmail.com> > > Wrong year. Except you started with that last year. > > > + > > +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 on 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 DTB built from the FreeBSD > source > > +tree matching the libbsd HEAD commit hash. > > If RTEMS is used together with libbsd the DTB should be build from the > FreeBSD source tree matching the commit that is used for `freebsd-org` > in libbsd. > > > + > > +Building the DTB > > +---------------- > > + > > +A single device tree source (DTS) 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 > > + > > Maybe already mention the -@ option here if someone wants to use overlays. > > > +For building the DTS 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 of how to build the device tree from the FreeBSD source. > > + > > +`NOTE : The following example uses FreeBSD master branch from github > mirror as > > I think there shouldn't be a space between NOTE and the colon, should > there? > > > +an example. It is advised to always use the source from the commit > matching the > > +libBSD HEAD.` > > ... matching `freebsd_org` 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 \ > > + $(pwd) > > + > > +Using Device Tree Overlay > > +------------------------- > > + > > +Device tree overlay is used either to add properties or devices to the > existing > > +device tree. Adding any property to DTS using an overlay will override > the > > +current values in the DTB. The Overlays enable us to modify the device > tree > > +using a small maintainable plugin without having to edit the whole Base > Tree. > > + > > +There are two ways of applying an overlay on top of the built dtb. > > + > > +#. Use fdtoverlay from libfdt > > + > > +#. Add the overlay in the root partition of the SDcard and apply it > using u-boot > > "U-Boot" - they use big letters on their home page: > http://www.denx.de/wiki/U-Boot. Please also fix that in the rest of the > text below. > > > + from the uEnv.txt file. > > uEnv.txt isn't a must. I think it's a Beagle convention (and maybe for > some other boards too). Just stop after "apply it using U-Boot" > > > + > > +The fdtoverlay command can be used as follows: > > + > > +.. code-block:: none > > + > > + fdtoverlay -i my-base-tree.dtb -o output-tree.dtb my-overlay.dtbo > > + > > +To apply it from u-boot during system initialization we have to add the > device > > +tree overlay file in the root directory of the SDcard and use uEnv.txt > to load > > +and apply the overlay. > > Again: SD card (by the way: There should be a space between SD and card > as far as I know) and uEnv.txt is for Beagle. > > > + > > +Below is a sample script that can be used as a reference to write the > uEnv.txt > > +properly so that it applies all the overlays (.dtbo): > > + > > +.. code-block:: shell > > + :linenos: > > + > > + overlays="fdt addr 0x88000000" > > + app=rtems-app.img > > + DTB_INSTALL_NAME=my-basetree.dtb > > + > > + for f in "$(pwd)"/*.dtbo > > + do > > + name=`basename "${f}"` > > + overlays="${overlays}; fatload mmc 0 0x88100000 ${name}; fdt > resize 0x1000; fdt apply 0x88100000" > > + done > > + echo "setenv bootdelay 5 > > + uenvcmd=run boot > > + boot=fatload mmc 0 0x80800000 $app ; fatload mmc 0 0x88000000 > ${DTB_INSTALL_NAME} ; ${overlays} ; bootm 0x80800000 - 0x88000000" >uEnv.txt > > I would suggest to only show the U-Boot commands (in multiple lines) > that are used to apply an overlay and not the script to generate a > uEnv.txt. Would most likely be more useful if someone tries to adapt it > to another board. > > > + > > 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 > > >
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