#
#Yocto - Build-system for the Linux kernel
#
#Yocto runs on Linux only, because it depends on a plethora of command line
#utilities and Python version 2.7. Another fine mess created by the UNIX
#"toolkit" philosophy, complete with a bag of seeds to organically grow a
#"build machine" which eventually nobody knows the specs for. We must pretend
#to subscribe to the idea of the build machine in order to take advantage of
#Yocto to build a customized Linux kernel. This file completely automates
#setting up a Yocto build environment, thereby ensuring that the Yocto
#environment is set up in exactly the same way every time.
#
#NOTE NOTE NOTE
#There are no BUILD_COMMANDs defined here. The modules defined here will
#simply install everything we need in order to run bitbake with a number of
#Bitbake layers. We must invoke bitbake manually. Bitbake may then in turn
#invoke cmake in order to build any user level code we have defined in any
#.bb layers we may have introduced. That user level code will be included in
#the bootable SD card image generated by bitbake.
#

#The Yocto system and all layers go under UNPACKED_ROOT
set (UNPACKED_ROOT "${CMAKE_INSTALL_PREFIX}/yocto")

ExternalProject_Add (
  yocto
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/poky
  BUILD_IN_SOURCE 1
  URL http://downloads.yoctoproject.org/releases/yocto/yocto-3.0.2/poky-zeus-22.0.2.tar.bz2
  URL_MD5 5a02a7114bc7e9d28d044f8a801c1f06
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
)

ExternalProject_Add (
  yocto-openembedded
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/meta-openembedded
  BUILD_IN_SOURCE 1
# URL https://github.com/openembedded/meta-openembedded/archive/zeus.zip
# Head of the Zeus branch per 24apr20 is
  URL https://github.com/openembedded/meta-openembedded/archive/9e60d30669a2ad0598e9abf0cd15ee06b523986b.zip
  URL_MD5 a35da1e4973b4611742f4fa2f2e38195
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  DEPENDS yocto
)

#To prevent wearing out the SD card on platforms where the boot medium is an
#SD card. All updates to the local bootable file system on the SD card will be 
#conceptually "rolled back" following a system restart.
ExternalProject_Add (
  yocto-readonly-rootfs-overlay
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/meta-readonly-rootfs-overlay
  BUILD_IN_SOURCE 1
# URL https://github.com/cmhe/meta-readonly-rootfs-overlay/archive/master.zip
# Head of the Master branch per 04may2020 is
  URL https://github.com/cmhe/meta-readonly-rootfs-overlay/archive/735aba8682471193d631eb08602b772b6c41cbb7.zip
  URL_MD5 d7dec15911aa2901885f084922a22bdf
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  DEPENDS yocto-openembedded
)

#Yocto Board Support Package (BSP) for Linux on Raspberry Pi
ExternalProject_Add (
  yocto-raspberrypi
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/meta-raspberrypi
  BUILD_IN_SOURCE 1
# URL https://github.com/agherzan/meta-raspberrypi/archive/zeus.zip
# Head of the Zeus branch per 24apr20 is
  URL https://github.com/agherzan/meta-raspberrypi/archive/0e05098853eea77032bff9cf81955679edd2f35d.zip
  URL_MD5 874fe5f9fd2524ccb84e6513d21c4f57
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  DEPENDS yocto-openembedded
)

ExternalProject_Add (
  yocto-hifiberry-rpi
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/meta-hifiberry-rpi
  BUILD_IN_SOURCE 1
# Head of the master branch per 28dec21 is
  URL https://github.com/mickey-happygolucky/meta-hifiberry-rpi/archive/5f71b99431e3b18db06040fd712618d871e3ebf9.zip
  URL_MD5 ed4b90c6e8b16da0118a30197f64947e
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  DEPENDS yocto-openembedded
)

#Yocto Board Support Package (BSP) for Linux on Beagleboard
ExternalProject_Add (
  yocto-beagleboard
  PREFIX ${CMAKE_INSTALL_PREFIX}
  SOURCE_DIR ${UNPACKED_ROOT}/meta-beagleboard
  BUILD_IN_SOURCE 1
  URL https://github.com/beagleboard/meta-beagleboard/archive/1.0.0.zip
  URL_MD5 459344cd3f6629f707d11e4d4bc04684
  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  DEPENDS yocto-openembedded
)

#Command to invoke "bitbake". Sets all required environment variables first.
#For example: "${BITBAKE_CMD} core-image-minimal -c populate_sdk_ext"
set (BITBAKE_CMD "${CMAKE_COMMAND} chdir ${UNPACKED_ROOT}/poky source ./oe-init-build-env && bitbake" PARENT_SCOPE)

#For use by other OSD modules that need to install their own Yocto layers.
#Yocto layer "A" must be installed under "${YOCTO_ROOT}/A". 
set (YOCTO_ROOT "${UNPACKED_ROOT}" PARENT_SCOPE)