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+---
+author: Sanchayan Maity
+title: Building a Board Support Package using Yocto
+tags: linux, yocto, openembedded
+---
+
+This post assumes a basic working knowledge of Yocto/OpenEmbedded.
+
+At my current workplace, for the project I am handling I am responsible for
+everything be it application, kernel configuration, custom drivers or existing
+driver enhancements or setting up the complete board support package for the
+system I am working on. I had worked on OpenEmbedded/Yocto at my previous
+company however, had no experience setting up a complete BSP. This meant having
+a custom meta layer for this project along with the required layers for Yocto
+to work and also the vendor specific layer which in this case was Xilinx, but,
+could be any for that matter. Accordingly, one would include meta-samsung,
+meta-ti or meta-intel and so on.
+
+One of the first decisions I had to make was regarding the flashing process. We
+had an eMMC on-board and also a SD card. I could have my own script and using
+u-boot's "mmc write" functions to format and write to the MMC. However, I decided
+to go the easier [genimage](https://github.com/pengutronix/genimage) approach.
+Yocto build system will build the relevant components and I could pack it in
+a single image using a configuration like below.
+
+```bash
+image boot.vfat {
+    vfat {
+        files = {
+            "BOOT.bin",
+            "emergency.ub",
+            "image.ub",
+            "system.dtb",
+            "Image"
+        }
+    }
+    size = 128M
+}
+
+image ged.img {
+    hdimage {
+    }
+
+    partition boot {
+        partition-type = 0xC
+        bootable = "true"
+        image = "boot.vfat"
+    }
+
+    partition rootfs {
+        partition-type = 0x83
+        image = "rootfs-zynqmp.ext4"
+        size = 0
+    }
+}
+```
+
+This gives a single file with an img extension which I can use to flash the SD
+card or eMMC using the **dd** command.
+
+Now, to use Yocto requires the use of several meta layers to be put together.
+One way is to use the repo tool which is also used in the Android world. However,
+I felt like I wanted something more along with Docker integration. Wondering if
+someone has already done this kind of work, I went searching on Google and came
+across [yoe-distro](https://github.com/YoeDistro/yoe-distro).
+
+yoe-distro provided a perfect template on which to base my work on. I only need
+integrate the layers I want and it could provide the rest. Docker integration
+was also included. Now, in case you are wondering why Docker is required, Yocto/
+OpenEmbedded builds can be quite sensitive to host distribution setup. Also in
+my case, Xilinx's support provided through Yocto would not build on Ubuntu 18.04
+which I am running at work. Downgrading would result in waste of time and is not
+actually a solution. Even if worked on Ubuntu 18.04, future upgrades may result
+in the build not working.
+
+Docker solves this problem by providing me a sandboxed environment, think of
+chroot or BSD jails simplified and on steroids. So I ended up integrating the
+vendor specific meta layers and added my own layer to provide customisations.
+Getting started with Yocto definitely requires putting in some effort, but,
+once you understand how to use it, adding customisations and stuff is lot easy
+or atleast has been quite easy for what I am doing.
+
+For example, I definitely need to build the kernel from my own source tree, since
+I have some patches of my own and if nothing else my own custom device trees
+which enable support for custom Xilinx IP core drivers. One problem I had was
+we internally use stash and trying to even just clone the source tree from stash
+requires authentication. I was not sure how to do this in Yocto while without
+exposing my ssh keys or account information. yoe-distro's setup helped here.
+
+The linux source is added as a submodule just like the meta layers and then a
+custom recipe builds that.
+
+```bash
+SRC_URI = "git://${TOPDIR}/sources/ged4k-linux-kernel;protocol=file;branch=ged4k_v2018.2"
+SRCREV = "fbec50e15d7b04f44690eb115d2cddd4423e0326"
+
+SRC_URI_append += " file://defconfig \
+                    file://fragment.cfg \
+                    "
+
+FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
+```
+
+You can see the protocol specified is not git, but file. Another simpler example
+is u-boot, where I just needed to apply my own patch on top of Xilinx's u-boot
+source and just the below in a recipe appending the original one.
+
+```bash
+FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
+SRC_URI_append = "\
+    file://0001-configs-xilinx_zynqmp-Config-SD-and-eMMC-boot-for-GE.patch \
+"
+```
+
+I had to include a rl78flash program which was not provided by any of the meta
+layers in Yocto and even that was easy. I looked at how some other recipes
+were written and came up with this and it just worked.
+
+```bash
+SUMMARY = "RL78 Flash Tool"
+DESCRIPTION = "Software to program RL78 microcontrollers via Serial Bootloader"
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
+
+SRCREV = "d0f5f05fbbce0a278658ca0caf67f293dcd26ee3"
+SRC_URI = "git://github.com/msalau/rl78flash.git;protocol=https;branch=master \
+          file://rl78flash.patch \
+          "
+
+S = "${WORKDIR}/git"
+
+EXTRA_OEMAKE = "'CC=${CC}' 'CFLAGS=${CFLAGS}'"
+
+do_compile() {
+    oe_runmake
+}
+
+do_install() {
+    install -d ${D}${bindir}
+    install -m 0755 ${WORKDIR}/git/rl78flash ${D}${bindir}
+}
+```
+
+It has been a lot fun learning how to put together a board support package and
+Yocto has given so much flexibility.
+
+
+