\subsection{Workflow}
\begin{frame}[fragile]
\includegraphics[width=\textwidth]{images/yocto-workflow}
\end{frame}

\begin{frame}[fragile]
\frametitle{retrieve poky}
\begin{verbatim}
% git clone http://git.yoctoproject.org/git/poky
% cd poky
% git checkout origin/pyro -b pyro -t
\end{verbatim}
\end{frame}

\begin{frame}[fragile]
\frametitle{prepare environment}
\begin{itemize}
\item bitbake is typically not installed into regular search paths
\item the environment of the bash is modified to find the commands
\item non-bash shells are not supported
\end{itemize}
\begin{verbatim}
% . ./oe-init-buildenv <builddir>
\end{verbatim}
\begin{itemize}
\item is used to modify the environment and change the CWD to <builddir>
\item ./oe-init-buildenv-memres is used to keep the bitbake-server running
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{classes}
\begin{itemize}
\item denoted by the .bbclass extension
\item base.bbclass is automatically included by all other classes and recipes.
\item common tasks and there execution order is defined in base.bbclass
\item tasks can be added, overridden, extended or used by other classes
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{recipes}
\begin{itemize}
\item a .bb file inherits classes and populates them with data
\item bitbake is used to schedule the tasks defined in a recipe
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{layers}
\begin{itemize}
\item a folder containing recipes, configs and classes
\item used to isolate different types of customizations from each other
\item e.g. own layer for machine specific stuff, one for own applications
\item extend, add, replace or modify recipes
\item add or replace class files
\item 'conf/layer.conf' is used to configure the layer
\item are added and ordered via BBLAYERS variable in build/conf/bblayers.conf
\item 'bitbake-layers show-layers' is used to show used layers
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{layers \#2}
layers should be grouped by functionality
\begin{itemize}
\item custom toolchains (compilers, debuggers, profiling tools)
\item distribution specifications (i.e. meta-yocto)
\item BSP/machine settings (i.e. meta-yocto-bsp)
\item functional areas (selinux, networking, etc)
\item project specific changes
\item a layer is typically organized as a git repository
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{directory layout}
\begin{verbatim}
poky
├── bitbake
├── documentation
├── meta
├── meta-selftest
├── meta-skeleton
├── meta-yocto
├── meta-yocto-bsp
└── scripts
\end{verbatim}
\end{frame}

\subsection{Variable assignments}
\begin{frame}
\frametitle{available operators}
\begin{itemize}
\item =
\item ?=
\item ??=
\item :=
\item += / =+
\item .= / =.
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{variable assignment with =}
\begin{verbatim}
VAR = "value"
\end{verbatim}
\begin{itemize}
\item normal assignment
\item values need to be surrounded by double quotes
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{early default assignment with ?=}
\begin{verbatim}
VAR ?= "1"
VAR ?= "2"
\end{verbatim}
\begin{itemize}
\item VAR is set to "1" in this example
\item if there are multiple assignments using ?= the first one is used
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{late default assignment with ??=}
\begin{verbatim}
VAR ??= "1"
VAR ??= "2"
\end{verbatim}
\begin{itemize}
\item VAR is set to "2" in this example
\item if there are multiple assignments using ??= the last one is used
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{assignment priorities \#1}
\begin{verbatim}
VAR_A ??= "12"
VAR_A ?= "34"

VAR_B ?= "12"
VAR_B ??= "34"
\end{verbatim}
\begin{itemize}
\item VAR\_A contains "34"
\item VAR\_B contains "12"
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{assignment priorities \#2}
\begin{verbatim}
VAR ?= "12"
VAR ??= "34"
VAR = "56"
VAR ?= "78"
VAR ??= "78"
\end{verbatim}
\begin{itemize}
\item VAR contains "56"
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{immediate variable expansion with :=}
\begin{verbatim}
VAR_A = "11"
VAR_B = "B:${VAR_A}"
VAR_A = "22"
VAR_C := "C:${VAR_A}"
VAR_A = "33"
echo ${VAR_A} ${VAR_B} ${VAR_C}
\end{verbatim}
\begin{itemize}
\item 33 B:33 C:22
\item the content of VAR\_C is expanded immediately on assignment
\item the content of VAR\_B is expanded on use
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{append (+=) or prepend (=+) a variable}
\begin{verbatim}
VAR_A = "12"
VAR_A += "34"
VAR_B = "56"
VAR_B =+ "78"
\end{verbatim}
\begin{itemize}
\item VAR\_A contains "12 34"
\item VAR\_B contains "78 56"
\item there are spaces between the appended values
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{append (.=) or prepend (=.) a variable}
\begin{verbatim}
VAR_A = "12"
VAR_A .= "34"
VAR_B = "56"
VAR_B =. "78"
\end{verbatim}
\begin{itemize}
\item VAR\_A contains "1234"
\item VAR\_B contains "7856"
\item there are no spaces between the appended values
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{assignment debugging}
\begin{verbatim}
$ echo 'FOO ??= "123"' >> conf/local.conf
$ echo 'FOO ?= "456"' >> conf/local.conf

$ bitbake -e | grep FOO
# $FOO [2 operations]
FOO="456"
\end{verbatim}
\end{frame}

\begin{frame}[fragile]
\frametitle{prepend/append}
\begin{verbatim}
VAR = "34"
VAR_append = "56"
VAR_prepend = "12"
\end{verbatim}
\begin{itemize}
\item VAR contains "123456"
\item there are no spaces between the appended values
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{overrides}
\begin{verbatim}
OVERRIDES="string1:string2"
VAR = "foo"
VAR_string1 = "bar"
\end{verbatim}
\begin{itemize}
\item if string1 is listed in OVERRIDES, use "bar" for value of VAR, otherwise use "foo"
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{variable flags}
\begin{verbatim}
VAR[some_flag]="foo"
\end{verbatim}
\begin{itemize}
\item associate a subsidiary flag value to a variable
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Key Expansion}
Key expansion happens when the BitBake datastore is finalized just before BitBake expands overrides.
\begin{verbatim}
A${B} = "X"
B = "2"
A2 = "Y"
\end{verbatim}
\begin{itemize}
\item Key expansion happens just before BitBake expands overrides.
\item A2 contains "X"
\end{itemize}
\end{frame}

\subsection{Recipes}
\begin{frame}
\frametitle{typical progressing}
\begin{enumerate}
\item fetch source files
\item extract sources
\item patch sources
\item configure sources
\item compilation
\item packaging
\end{enumerate}
\end{frame}

\begin{frame}[fragile]
\frametitle{skeleton}
\begin{verbatim}
SUMMARY = "short description of the package (1 line)"
DESCRIPTION = "a long version of the description of the package"
HOMEPAGE = "http://url-of-the-os-project.org"
LICENSE = "LGPLv2.1"

LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \
                    file://licfile1.txt;beginline=5;endline=29;md5=yyyy \
                    file://licfile2.txt;endline=50;md5=zzzz

SRC_URI = "file://mysw-1.0.tbz"
SRC_URI[md5sum] = "xxx"
SRC_URI[sha256sum] = "yyy"

S = "${WORKDIR}/${PN}-${PV}"

inherit autotools
\end{verbatim}
\end{frame}

\begin{frame}
\frametitle{syntax}
a recipe normaly consists of a human readable description of the project and
references to the open-source project and:
\begin{description}
\item[LIC*] reference to the used licenses
\item[SRC\_URI] list of source files (local or remote)
\item[PV] package-version (retrived from filename name\_version.bb)
\item[PN] package-name (retrived from filename name\_version.bb)
\item[P] ${PN}-${PV}
\item[S] The location in the Build Directory where unpacked recipe source code resides.
\item[inherit] use a class (or multiple classes)
\end{description}
\end{frame}

\begin{frame}
\frametitle{the LICENSE variable}
list of source licenses for the recipe:
\begin{itemize}
\item do not use spaces within individual license names
\item use spaces between license names
\item separate license names using | (pipe) when there is a choice between
 licenses
\item separate license names using \& (AND) if parts of the code are licensed
 with different licenses
\item for standard licenses, use the names of the files in
 meta/files/common-licenses/ or the SPDXLICENSEMAP
 \footnote{aps commonly used license names to their SPDX counterparts found in
 meta/files/common-licenses/. For the default SPDXLICENSEMAP mappings, see the
 meta/conf/licenses.conf file}
 flag names defined in meta/conf/licenses.conf
\item use "CLOSED" for closed source software
 (LIC\_FILES\_CHKSUM is not needed to be defined then)
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{LIC\_FILE\_CHKSUM variable}
Checksums of the license text in the recipe source code.
\vspace{2em}


This variable tracks changes in license text of the source code files.
If the license text is changed, it will trigger a build failure,
which gives the developer an opportunity to review any license change.
\end{frame}

\begin{frame}[fragile]
\frametitle{SRC\_URI variable}
\begin{verbatim}
SRC_URI = "<protocol>://<host>/<path>;<OptionA=xxx>;<OptionB=xxx>"
\end{verbatim}
multiple urls can be set in a SRC\_URI variable:
\begin{verbatim}
SRC_URI = "<url1>;name=url1 <url2>;name=url2"
\end{verbatim}
for each url a md5 and sha256 checksum needs to be added:
\begin{verbatim}
SRC_URI[url1.md5sum] = xxx
SRC_URI[url1.sha256sum] = yyy
SRC_URI[url2.md5sum] = zzz
SRC_URI[url2.sha256sum] = xyz
\end{verbatim}
To get these checksums don't specify them and run a build and copy them from
the error message. (Don't use md5sum or sha256sum on the commandline; they
produce a different checksum.)
\end{frame}

\begin{frame}[fragile]
\frametitle{local SRC\_URI (file://)}
The path is relative to the FILESPATH variable. To modify the FILESPATH use
FILESEXTRAPATH.
\vspace{2em}


Additional files are searched in subdirectories of the directory in which the
recipe file (.bb) or append file (.bbappend) resides.

To find out which paths can be used, it is best practice to use
\begin{verbatim}
$ bitbake -e <recipe-name> | grep FILESPATH
\end{verbatim}
\end{frame}

\begin{frame}
\frametitle{remote SRC\_URI}
\begin{description}
\item[bzr://]Bazaar revision control repository
\item[git://]Git revision control repository
\item[osc://]OSC (OpenSUSE Build service) revision control repository
\item[ccrc://]ClearCase repository
\item[http://]Internet using http
\item[https://]Internet using https
\item[ftp://]Internet using ftp
\item[cvs://]CVS revision control repository
\item[hg://]Mercurial (hg) revision control repository
\item[p4://]Perforce (p4) revision control repository
\item[ssh://]secure shell
\item[svn://]Subversion (svn) revision control repository
\end{description}
\end{frame}

\begin{frame}
\frametitle{SRC\_URI patch options}
\begin{itemize}
\item patches are applied in the order they appear in SRC\_URI
\item quilt is used to apply the patches
\end{itemize}
\begin{description}
\item[apply=no] apply patch or not; default is yes
\item[striplevel=0] striplevel to use when applying a patch; default is 1
\item[patchdir=\${S}/foo] directory in which the patch should be applied;
 default is \${S}
\end{description}
\end{frame}

\begin{frame}
\frametitle{SRC\_URI patch options \#2}
\begin{description}
\item[mindate] apply patch only if SRCDATE
 \footnote{The date of the source code used to build the package.
 This variable applies only if the source was fetched from a
 Source Code Manager (SCM)} is equal to or greater than mindate
\item[maxdate] apply patch only if SRCDATE is not later than maxdate
\item[minrev] apply the patch only if SRCREV
 \footnote{The revision of the source code used to build the package.
 This variable applies to Subversion, Git, Mercurial and Bazaar only}
 is equal to or greater than minrev
\item[maxrev] apply patch only if SRCREV is not later than maxrev
\item[rev] apply patch only if SRCREV is equal to rev
\item[notrev] apply patch only if SRCREV is not equal to rev
\end{description}
\end{frame}

\begin{frame}
\frametitle{SRC\_URI options}
\begin{description}
\item[unpack=no] controls if an archive is unpacked; default is yes
\item[subdir=bla] places the file (or extracts its contents) into the
 specified subdirectory of WORKDIR
 \footnote{${TMPDIR}/work/${MULTIMACH\_TARGET\_SYS}/${PN}/${EXTENDPE}${PV}-${PR}; 
 eg. poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0}
\item[name=mydl] name to be used for association with SRC\_URI checksums when
 you have more than one file specified in SRC\_URI
\item[downloadfilename=my.tar.gz] the filename used when storing the downloaded file
\end{description}
\end{frame}

\begin{frame}
\frametitle{inherit}
inherit is used to use the functionality defined in a .bblcass file. Popular
predefined classes are:
\begin{itemize}
\item autotools
\item cmake
\item cpan
\item distutils / setuptools
\item kernel / module
\item mime
\item qmake / qmake2
\item qt4e / qt4x11
\item scons
\item systemd
\item u-boot
\item vala
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{include}
Includes a complete file
\begin{itemize}
\item include examle-defs.inc
\item includes the first file it can find within BBPATH
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{require}
Same as include, but returns an error, if include file not found.
\begin{itemize}
\item includes the first file it can find within BBPATH
\end{itemize}
\end{frame}

\subsection{Append files}
\begin{frame}
\frametitle{basics}
\begin{itemize}
\item are typically used to modify or extend the functionality of the base
        recipe
\item it's recommended by the Yocto project to use bbappend files instead
        of copying and modyfiing a recipe in an own layer
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{naming}
an append file must be named after the base package:
\begin{verbatim}
<base-pn>_<base-pv>.bbappend
\end{verbatim}
\end{frame}

\subsection{Classes}
\begin{frame}
\frametitle{basics}
\begin{itemize}
\item python can be used to write functions
\item e.g. write your own image generation class
\end{itemize}
\end{frame}

\subsection{Tasks}
\begin{frame}
\frametitle{basics}
\begin{itemize}
\item are defined and ordered in classes
\item can be overridden by classes and recipes
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{download \& patch}
\begin{description}
\item [do\_checkuri] validates the SRC\_URI value
\item [do\_checkuriall] validates the SRC\_URI value for all recipes required
        to build a target"
\item [do\_fetch] fetches the source code
\item [do\_fetchall] fetches all remote sources required to build a target
\item [do\_unpack] unpacks the source code into a working directory
\item [do\_patch] locates patch files and applies them to the source code
\end{description}
\end{frame}

\begin{frame}
\frametitle{configure \& compile}
\begin{description}
\item [do\_configure] configures the source by enabling and disabling any
        build-time and configuration options for the software being built
\item [do\_configure\_ptest\_base] configures the runtime test suite included
        in the software being built
\item [do\_compile] compiles the source in the compilation directory
\item [do\_install] copies files from the compilation directory to a holding
        area
\item [do\_populate\_sysroot] copies a subset of files installed by
        do\_install into the sysroot in order to make them available to other
        recipes
\end{description}
\end{frame}

\begin{frame}
\frametitle{packaging}
\begin{description}
\item [do\_packagedata] creates package metadata used by the build system to
        generate the final packages
\item [do\_package] analyzes the content of the holding area and splits it
        into subsets based on available packages and files
\item [do\_package\_write] creates the actual packages and places them in the
        Package Feed area
\item [do\_package\_write\_deb] creates the actual DEB packages and places
        them in the Package Feed area
\item [do\_package\_write\_ipk] creates the actual IPK packages and places
        them in the Package Feed area
\item [do\_package\_write\_rpm] creates the actual RPM packages and places
        them in the Package Feed area
\item [do\_package\_write\_tar] creates tar archives for packages and places
        them in the Package Feed area
\item [do\_package\_index] creates or updates the index in the Package Feed
        area
\end{description}
\end{frame}

\begin{frame}
\frametitle{deploy}
\begin{description}
\item [do\_rootfs] creates the root filesystem (file and directory structure)
        for an image
\item [do\_vmdkimg] creates a .vmdk image for use with VMware and compatible
        virtual machine hosts"
\item [do\_deploy] writes deployable output files to the deploy directory
\item [do\_populate\_sdk] creates the file and directory structure for an
        installable SDK
\end{description}
\end{frame}

\begin{frame}
\frametitle{cleanup}
\begin{description}
\item [do\_clean] removes all output files for a target
\item [do\_cleanall] removes all output files, shared state cache, and
        downloaded source files for a target
\item [do\_cleansstate] removes all output files and shared state cache for a
        target
\item [do\_rm\_work] removes work files after the build system has finished
        with them
\item [do\_rm\_work\_all] top-level task for removing work files after the
        build system has finished with them
\end{description}
\end{frame}

\begin{frame}
\frametitle{kernel}
\begin{description}
\item [do\_kernel\_checkout] checks out source/meta branches for a linux-yocto
        style kernel
\item [do\_validate\_branches] ensures that the source/meta branches are on
        the locations specified by their SRCREV values for a linux-yocto style
        kernel"
\item [do\_kernel\_configme] assembles the kernel configuration for a
        linux-yocto style kernel
\item [do\_menuconfig] runs 'make menuconfig' for the kernel
\item [do\_diffconfig] compares the old and new config files after running
        do\_menuconfig for the kernel
\item [do\_savedefconfig] creates a minimal Linux kernel configuration file
\item [do\_kernel\_configcheck] validates the kernel configuration for a
        linux-yocto style kernel
\item [do\_sizecheck] checks the size of the kernel image against
        KERNEL\_IMAGE\_MAXSIZE (if set)
\end{description}
\end{frame}

\begin{frame}
\frametitle{kernel}
\begin{description}
\item [do\_compile\_kernelmodules] compiles loadable modules for the Linux
        kernel
\item [do\_strip] strips unneeded sections out of the Linux kernel image
\item [do\_kernel\_link\_vmlinux] creates a symbolic link in arch/\$arch/boot
        for vmlinux kernel images
\item [do\_bundle\_initramfs] combines an initial ramdisk image and kernel
        together to form a single image
\end{description}
\end{frame}

\begin{frame}
\frametitle{licenses}
\begin{description}
\item [do\_populate\_lic] writes license information for the recipe that is
        collected later when the image is constructed
\item [do\_spdx] a build stage that takes the source code and scans it on a
        remote FOSSOLOGY server in order to produce an SPDX document
\end{description}
\end{frame}

\begin{frame}
\frametitle{special stuff}
\begin{description}
\item [do\_uboot\_mkimage] creates a uImage file from the kernel for the
        U-Boot bootloader
\item [do\_generate\_qt\_config\_file] writes a qt.conf file for building a
        Qt-based application
\item [do\_devshell] starts a shell with the environment set up for
        development/debugging
\item [do\_listtasks] lists all defined tasks for a target
\end{description}
\end{frame}

\subsection{Machines}
\begin{frame}
\frametitle{basics}
a machine config is used to describe a board
\begin{itemize}
\item machine configs are stored in the layers: conf/machine/*
\item settings can be splitted in different include *.inc files
\item e.g. one include for CPU that is used by the SoC inc file,
that is used by the Board .conf file
\item the include files can be stored in different layers
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{u-boot \& kernel}
\begin{description}
\item [UBOOT\_MACHINE] value passed on the make command line when building a
        U-Boot image
\item [UBOOT\_MAKE\_TARGET] target called in the Makefile
\item [UBOOT\_ENTRYPOINT] entry point for the U-Boot image
\item [PREFERRED\_PROVIDER\_virtual/kernel] default kernel
\item [KERNEL\_DEVICETREE] default devicetree
\item [KERNEL\_IMAGETYPE] type of kernel to build for a device,
        defaults to 'zImage'
\end{description}
\end{frame}

\begin{frame}
\frametitle{hardware}
\begin{description}
\item[SOC\_FAMILY] groups together machines based upon the same family of SOC
        (System On Chip)
\item [MACHINEOVERRIDES] lists overrides specific to the current machine.
        By default, this list includes the value of MACHINE. This can be used in
        recipes; e.g. MACHINEOVERRIDES =. "mymachine" and in the recipe
        SRC\_URI\_append\_mymachine = "file://mymachine-quirk.patch"
\item [MACHINE\_FEATURES] list of hardware features the MACHINE supports
\footnote{acpi, alsa, apm, bluetooth, ext2, irda, keyboard, pci, pcmcia,
        screen, serial, touchscreen, usbgadget, usbhost, wifi}
\item [MACHINE\_EXTRA\_RRECOMMENDS] list of machine-specific packages to
        install as part of the image being built that are not essential for booting
        the machine. The image being built has no build dependencies on the packages
        in this list.
\item [SERIAL\_CONSOLE] speed and device for the serial port used to attach
        the serial console. This variable is given to the kernel as the 'console'
        parameter. After booting occurs, getty is started on that port so remote
        login is possible.
\end{description}
\end{frame}

\begin{frame}
\frametitle{compiler settings}
\begin{description}
\item [DEFAULTTUNE] e.g. armv6hf or cortexa8hf-neon, x86-64, \dots
\item [TUNE\_FEATURES] e.g. "armv7a vfp neon"
\item [TUNEVALID] Descriptions, stored as flags, of valid tuning features
\item [TUNECONFLICTS] list of conflicting features for a given feature
\end{description}
\end{frame}

\begin{frame}
\frametitle{software}
\begin{description}
\item [PREFERRED\_VERSION\_xserver-xorg] compatible xserver version
\item [PREFERRED\_PROVIDER\_virtual/kernel] recommended kernel
\item [IMAGE\_FSTYPES] formats for the rootfs, e.g. "ext3 tar.bz2"
\item [IMAGE\_CLASSES] list of classes that all images should inherit, default
        is image\_types, e.g. to hook in own image generation code
\end{description}
\end{frame}