= Preface =
This guide is written in a way that forces the reader to manually perform every step, excluding environment variables via the setup script because I want to be able to change those. If you would like to follow the official guide provided by beagleboard, which is far more streamlined and automated, please see the references at the bottom of this document.

'''WARNING''' This guide is very much still a work in progress. Do not expect anything to work yet.

= Prerequisites =
    emerge -a sys-block/bmap-tools sys-fs/genimage dev-libs/libyaml sys-fs/mtools
    mkdir beaglev-fire-gentoo && cd beaglev-fire-gentoo
    export PROJECT_ROOT="$PWD"
    # the target directory will be where we store relevant parts of our target image before we turn it into an image
    # the boot dir will contain the linux image, hss payloads, and anything else needed to boot
    mkdir -p target/boot target/rootfs
    # The tools directory will contain anything needed to generate pieces of the image. The HSS payload generator is one example of this
    mkdir tools
    # We will store any temporary downloads we need here, like the stage3 tarball
    mkdir downloads

== Using the riscv toolchain provided via crossdev ==
Crossdev is required for this step. If you don’t have crossdev set up, use [https://wiki.gentoo.org/wiki/Crossdev this] guide to install it. At the time of writing this, crossdev installs riscv64-unknown-linux-gnu-gcc 13.2.1. This is note worthy because the official beagleboard guide uses 11.4. If there are issues with this toolchain, use the precompiled toolchain via these steps.

    crossdev -t riscv64-unknown-linux-gnu
    export RISCV64_CC="riscv64-unknown-linux-gnu-"

== Using a precompiled toolchain ==
    mkdir mirror
    mkdir toolchain
    export GCC_VERSION=11.4.0
    wget -c --directory-prefix=./mirror/ "https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/${GCC_VERSION}/x86_64-gcc-${GCC_VERSION}-nolibc-riscv64-linux.tar.xz"
    
    tar xvf ./mirror/x86_64-gcc-${GCC_VERSION}-nolibc-riscv64-linux.tar.xz --strip-components=2 -C ./toolchain/
    export RISCV64_CC="$PWD/toolchain/bin/riscv64-linux-"

From this point forward, instructions will use the <code>RISCV64_CC</code> variable as the toolchain.

'''WARNING''': Using the precompiled toolchain instead of the toolchain provided by crossdev means the chroot and qemu steps likely won&rsquo;t work. More information on this will be added later, but in the meantime just know that if you don&rsquo;t use the crossdev toolchain, you&rsquo;ll need to skip cross emerging and chrooting. This just means you&rsquo;ll need to compile and configure on the device instead after the first boot. Using the toolchain provided by crossdev is highly recommended.

Export some other misc. environment variables:

    export HSS_BRANCH="v2023.02"
    export HSS_REPO="https://github.com/polarfire-soc/hart-software-services.git"
    export UBOOT_BRANCH="linux4microchip+fpga-2023.02"
    export UBOOT_REPO="https://github.com/polarfire-soc/u-boot.git"
    export GIT_DEPTH=20
    export CORES=$(getconf _NPROCESSORS_ONLN)

== Configuring QEMU-user and binfmt ==
In a perfect world, producing a rootfs from scratch would simply mean downloading the tarball, unwrapping it into the destined rootfs folder, and running a few scripts to set it up. However, sometimes it can be useful to install a package or configure the system before deploying it to the target device. We can use [https://wiki.gentoo.org/wiki/Embedded_Handbook/General/Compiling_with_qemu_user_chroot qemu-user] to [https://wiki.gentoo.org/wiki/Chroot chroot] into our target system to do these things.

=== Prepare to install QEMU ===
    echo 'QEMU_SOFTMMU_TARGETS="riscv64 x86_64"' >> /etc/portage/make.conf
    echo 'QEMU_USER_TARGETS="riscv64"' >> /etc/portage/make.conf
    echo app-emulation/qemu static-user >> /etc/portage/package.use/qemu

=== Install QEMU ===
    emerge --ask --update --newuse --deep app-emulation/qemu

Now create a binary package for QEMU. This is done so that we can install it into our target system to run chroot properly.

    quickpkg app-emulation/qemu

Non-root users will need access to use qemu.

    usermod -aG kvm,qemu $USER

=== Specifying a riscv64 binfmt-misc handler for systemd-binfmt ===
==== Option A: Using the default binfmt configuration file shipped with qemu ====
&ldquo;For the systemd-binfmt service, add files containing the desired handler registration strings under ''etc/binfmt.d''. Modern versions of qemu ship a binfmt configuration file that supports all binary formats. Simply link it to /etc for binary format support, then skip the following manual file creation steps.&rdquo; - [https://wiki.gentoo.org/wiki/Embedded_Handbook/General/Compiling_with_qemu_user_chroot Gentoo Embedded Handbook]

    ln -s /usr/share/qemu/binfmt.d/qemu.conf /etc/binfmt.d/qemu.conf

This supports ''all'' default architectures in the default <code>qemu.conf</code>. If you only want to support riscv64, use the instructions below.

==== Option B: Adding support for just riscv64 ====
    echo -E ':riscv64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-riscv64:' > /etc/binfmt.d/qemu-riscv64-static.conf

Now restart the service to register the binary formats:

    systemctl restart systemd-binfmt

See the <code>chroot instructions below</code>

= Clone & Build Heart Software Services (HSS) =
== Clone HSS ==
    if [ -d ./hart-software-services/ ] ; then
    	rm -rf ./hart-software-services/ || true
    fi
    git clone -b ${HSS_BRANCH} ${HSS_REPO} ./hart-software-services/ --depth=${GIT_DEPTH}

== Build HSS ==
    make -C hart-software-services/tools/hss-payload-generator/ clean
    make -C hart-software-services/tools/hss-payload-generator/

= Clone & Build u-boot =
== Clone u-boot ==
    # remove old if it exists, optional
    if [ -d ./u-boot ] ; then
    	rm -rf ./u-boot || true
    fi
    git clone -b ${UBOOT_BRANCH} ${UBOOT_REPO} ./u-boot/ --depth=${GIT_DEPTH}

== Download the patches ==
The patches currently exist as part of BeagleV&rsquo;s <code>BeagleV-Fire-ubuntu</code> repo, so we&rsquo;ll just clone the whole thing for now. Eventually, I&rsquo;ll see if I can mirror just the patches somewhere.

    git clone https://git.beagleboard.org/beaglev-fire/BeagleV-Fire-ubuntu.git ./beaglev --depth=${GIT_DEPTH}

== WIP Build u-boot ==
    # Apply patches to uboot
    cp -v ./beaglev/patches/u-boot/beaglev-fire/microchip_mpfs_icicle.h ./u-boot/include/configs/microchip_mpfs_icicle.h
    cp -v ./beaglev/patches/u-boot/beaglev-fire/microchip-mpfs-icicle-kit.dts ./u-boot/arch/riscv/dts/
    cp -v ./beaglev/patches/u-boot/beaglev-fire/microchip_mpfs_icicle_defconfig ./u-boot/configs/microchip_mpfs_icicle_defconfig
    make -C u-boot ARCH=riscv CROSS_COMPILE=${RISCV64_CC} microchip_mpfs_icicle_defconfig
    # if you want to make configurations....
    # make -C u-boot ARCH=riscv CROSS_COMPILE=${RISCV64_CC} menuconfig
    make -C u-boot ARCH=riscv CROSS_COMPILE=${RISCV64_CC} olddefconfig
    make -C u-boot ARCH=riscv CROSS_COMPILE=${RISCV64_CC} savedefconfig
    cp -v ./u-boot/defconfig ./u-boot/configs/microchip_mpfs_icicle_defconfig
    cp -v ./u-boot/defconfig ./beaglev/patches/u-boot/beaglev-fire/microchip_mpfs_icicle_defconfig
    make -C u-boot -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV_CC} all
    # copy the generated uboot into our boot folder
    cp -v ./u-boot/u-boot.bin ./target/boot/u-boot.bin
    # i have no idea why 2 copies are being made, one u-boot.bin and one src.bin
    cp -v ./u-boot/u-boot.bin ./target/boot/src.bin

= TODO Build the Linux kernel =
    cd ./beaglev/linux/
    if [ ! -f ./.patched ] ; then
    	if [ -f arch/riscv/configs/mpfs_defconfig ] ; then
    		git am ../patches/linux/0002-PCIe-Change-controller-and-bridge-base-address.patch
    		git am ../patches/linux/0003-GPIO-Add-Microchip-CoreGPIO-driver.patch
    		git am ../patches/linux/0004-ADC-Add-Microchip-MCP356X-driver.patch
    		git am ../patches/linux/0005-Microchip-QSPI-Add-regular-transfers.patch
    		git am ../patches/linux/0006-BeagleV-Fire-Add-printk-to-IM219-driver-for-board-te.patch
    		git am ../patches/linux/0007-MMC-SPI-Hack-to-support-non-DMA-capable-SPI-ctrl.patch
    		git am ../patches/linux/0008-Add-wireless-regdb-regulatory-database-file.patch
    		git am ../patches/linux/0009-Makefile-build-mpfs-beaglev-fire.dtb.patch
    	fi
    	touch .patched
    fi
    
    if [ -f arch/riscv/configs/mpfs_defconfig ] ; then
    	cp -v ../device-tree/src/microchip/mpfs-beaglev-fire.dts arch/riscv/boot/dts/microchip/
    	cp -v ../device-tree/src/microchip/mpfs-beaglev-fire-fabric.dtsi arch/riscv/boot/dts/microchip/
    fi
    
    echo "make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} clean"
    make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} clean
    
    if [ -f arch/riscv/configs/mpfs_defconfig ] ; then
    	cp -v ../patches/linux/mpfs_defconfig ./arch/riscv/configs/mpfs_defconfig
    
    	echo "make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} mpfs_defconfig"
    	make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} mpfs_defconfig
    
    	./scripts/config --set-str CONFIG_LOCALVERSION "-$(date +%Y%m%d)"
    
    	./scripts/config --enable CONFIG_CRYPTO_USER_API_HASH
    	./scripts/config --enable CONFIG_CRYPTO_USER_API_SKCIPHER
    	./scripts/config --enable CONFIG_KEY_DH_OPERATIONS
    	./scripts/config --enable CONFIG_CRYPTO_ECB
    	./scripts/config --enable CONFIG_CRYPTO_MD4
    	./scripts/config --enable CONFIG_CRYPTO_MD5
    	./scripts/config --enable CONFIG_CRYPTO_CBC
    	./scripts/config --enable CONFIG_CRYPTO_SHA256
    	./scripts/config --enable CONFIG_CRYPTO_AES
    	./scripts/config --enable CONFIG_CRYPTO_DES
    	./scripts/config --enable CONFIG_CRYPTO_CMAC
    	./scripts/config --enable CONFIG_CRYPTO_HMAC
    	./scripts/config --enable CONFIG_CRYPTO_SHA512
    	./scripts/config --enable CONFIG_CRYPTO_SHA1
    
    	echo "make -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV64_CC} olddefconfig"
    	make -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV64_CC} olddefconfig
    else
    	echo "make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} defconfig"
    	make ARCH=riscv CROSS_COMPILE=${RISCV64_CC} defconfig
    
    	./scripts/config --enable CONFIG_PCIE_MICROCHIP_HOST
    
    	./scripts/config --enable CONFIG_OF_OVERLAY
    
    	./scripts/config --enable CONFIG_I2C
    	./scripts/config --enable CONFIG_EEPROM_AT24
    	./scripts/config --enable CONFIG_I2C_MICROCHIP_CORE
    
    	./scripts/config --enable CONFIG_SPI_MICROCHIP_CORE
    	./scripts/config --enable CONFIG_SPI_MICROCHIP_CORE_QSPI
    	./scripts/config --module CONFIG_SPI_SPIDEV
    
    	./scripts/config --enable CONFIG_GPIO_SYSFS
    
    	./scripts/config --enable CONFIG_HW_RANDOM_POLARFIRE_SOC
    
    	./scripts/config --enable CONFIG_USB_MUSB_HDRC
    	./scripts/config --enable CONFIG_NOP_USB_XCEIV
    	./scripts/config --enable CONFIG_USB_MUSB_POLARFIRE_SOC
    	./scripts/config --enable CONFIG_USB_MUSB_DUAL_ROLE
    
    	./scripts/config --enable CONFIG_MAILBOX
    	./scripts/config --enable CONFIG_POLARFIRE_SOC_MAILBOX
    	./scripts/config --disable CONFIG_SUN6I_MSGBOX
    
    	./scripts/config --enable CONFIG_REMOTEPROC
    	./scripts/config --enable CONFIG_REMOTEPROC_CDEV
    
    	./scripts/config --enable CONFIG_POLARFIRE_SOC_SYS_CTRL
    
    	./scripts/config --enable CONFIG_USB_GADGET
    	./scripts/config --enable CONFIG_USB_CONFIGFS
    	./scripts/config --enable CONFIG_CONFIGFS_FS
    	./scripts/config --enable CONFIG_USB_CONFIGFS_SERIAL
    	./scripts/config --enable CONFIG_USB_CONFIGFS_ACM
    	./scripts/config --enable CONFIG_USB_CONFIGFS_OBEX
    	./scripts/config --enable CONFIG_USB_CONFIGFS_NCM
    	./scripts/config --enable CONFIG_USB_CONFIGFS_ECM
    	./scripts/config --enable CONFIG_USB_CONFIGFS_ECM_SUBSET
    	./scripts/config --enable CONFIG_USB_CONFIGFS_RNDIS
    	./scripts/config --enable CONFIG_USB_CONFIGFS_EEM
    	./scripts/config --enable CONFIG_USB_CONFIGFS_PHONET
    	./scripts/config --enable CONFIG_USB_CONFIGFS_MASS_STORAGE
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_LB_SS
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_FS
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_UAC1
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_UAC2
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_MIDI
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_HID
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_UVC
    	./scripts/config --enable CONFIG_USB_CONFIGFS_F_PRINTER
    
    	./scripts/config --module CONFIG_MEDIA_SUPPORT
    	./scripts/config --enable CONFIG_MEDIA_SUPPORT_FILTER
    	./scripts/config --enable CONFIG_MEDIA_SUBDRV_AUTOSELECT
    	./scripts/config --enable CONFIG_MEDIA_CAMERA_SUPPORT
    	./scripts/config --module CONFIG_VIDEO_IMX219
    
    	./scripts/config --module CONFIG_IIO
    
    	#Cleanup large DRM...
    	./scripts/config --disable CONFIG_DRM
    	./scripts/config --disable CONFIG_DRM_RADEON
    	./scripts/config --disable CONFIG_DRM_NOUVEAU
    	./scripts/config --disable CONFIG_DRM_SUN4I
    
    	#Optimize:
    	./scripts/config --enable CONFIG_IP_NF_IPTABLES
    	./scripts/config --enable CONFIG_NETFILTER_XTABLES
    	./scripts/config --enable CONFIG_NLS_ISO8859_1
    	./scripts/config --enable CONFIG_BLK_DEV_DM
    
    	./scripts/config --set-str CONFIG_LOCALVERSION "-$(date +%Y%m%d)"
    
    	echo "make -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV64_CC} olddefconfig"
    	make -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV64_CC} olddefconfig
    fi
    
    echo "make -j${CORES} ARCH=riscv CROSS_COMPILE=${RISCV64_CC} Image modules dtbs"
    make -j${CORES} ARCH=riscv CROSS_COMPILE="ccache ${RISCV64_CC}" Image modules dtbs
    
    if [ ! -f ./arch/riscv/boot/Image ] ; then
    	echo "Build Failed"
    	exit 2
    fi
    
    KERNEL_UTS=$(cat "${PROJECT_ROOT}/linux/include/generated/utsrelease.h" | awk '{print $3}' | sed 's/\"//g' )
    
    if [ -d "${PROJECT_ROOT}/deploy/tmp/" ] ; then
    	rm -rf "${PROJECT_ROOT}/deploy/tmp/"
    fi
    mkdir -p "${PROJECT_ROOT}/deploy/tmp/"
    
    make -s ARCH=riscv CROSS_COMPILE=${RISCV64_CC} modules_install INSTALL_MOD_PATH="${PROJECT_ROOT}/deploy/tmp"
    
    if [ -f "${PROJECT_ROOT}/deploy/${KERNEL_UTS}-modules.tar.gz" ] ; then
    	rm -rf "${PROJECT_ROOT}/deploy/${KERNEL_UTS}-modules.tar.gz" || true
    fi
    echo "Compressing ${KERNEL_UTS}-modules.tar.gz..."
    echo "${KERNEL_UTS}" > "${PROJECT_ROOT}/deploy/.modules"
    cd "${PROJECT_ROOT}/deploy/tmp" || true
    tar --create --gzip --file "../${KERNEL_UTS}-modules.tar.gz" ./*
    cd "${PROJECT_ROOT}/linux/" || exit
    rm -rf "${PROJECT_ROOT}/deploy/tmp" || true
    
    if [ -f arch/riscv/configs/mpfs_defconfig ] ; then
    	cp -v ./.config ../patches/linux/mpfs_defconfig
    	cp -v ./arch/riscv/boot/dts/microchip/mpfs-beaglev-fire.dts ../patches/linux/dts/mpfs-beaglev-fire.dts
    	cp -v ./arch/riscv/boot/dts/microchip/mpfs-beaglev-fire-fabric.dtsi ../patches/linux/dts/mpfs-beaglev-fire-fabric.dtsi
    else
    	cp -v ./.config ../patches/linux/mainline/defconfig
    	cp -v ./arch/riscv/boot/dts/microchip/mpfs-beaglev-fire.dts ../patches/linux/mainline/dts/mpfs-beaglev-fire.dts
    	cp -v ./arch/riscv/boot/dts/microchip/mpfs-beaglev-fire-fabric.dtsi ../patches/linux/mainline/dts/mpfs-beaglev-fire-fabric.dtsi
    fi
    if [ ! -d ../deploy/input/ ] ; then
    	mkdir -p ../deploy/input/ || true
    fi
    cp -v ./arch/riscv/boot/Image ../deploy/input/
    cp -v ./arch/riscv/boot/dts/microchip/mpfs-beaglev-fire.dtb ../deploy/input/
    
    cd ../
    
    cp -v ./patches/linux/beaglev_fire.its ./deploy/input/
    cd ./deploy/input/
    gzip -9 Image -c > Image.gz
    if [ -f ../../u-boot/tools/mkimage ] ; then
    	../../u-boot/tools/mkimage -f beaglev_fire.its beaglev_fire.itb
    fi

= WIP Generate the HSS payload =
    cd ./deploy/
    
    if [ -f ./src.bin ] ; then
    	if [ ! -d ./input/ ] ; then
    		mkdir ./input/
    	fi
    
    	if [ -f ./input/payload.bin ] ; then
    		rm -rf ./input/payload.bin || true
    	fi
    
    	./hss-payload-generator -vv -c config.yaml ./input/payload.bin
    
    	date
    	unset test_var
    	test_var=$(strings ./u-boot.bin | grep 'U-Boot 20' | head -n1 || true)
    	if [ ! "x${test_var}" = "x" ] ; then
    		echo "[u-boot.bin: ${test_var}]"
    	fi
    
    	unset test_var
    	test_var=$(strings ./src.bin | grep 'U-Boot 20' | head -n1 || true)
    	if [ ! "x${test_var}" = "x" ] ; then
    		echo "[src.bin:    ${test_var}]"
    	fi
    
    	unset test_var
    	test_var=$(strings ./input/payload.bin | grep 'U-Boot 20' | head -n1 || true)
    	if [ ! "x${test_var}" = "x" ] ; then
    		echo "[payload.bin:${test_var}]"
    	fi
    fi
    
    #

= WIP Installing the RootFS =
== Download and installing a stage tarball ==
This guide uses the systemd-mergedusr profile by default. Other profiles have not been tested.

    wget https://distfiles.gentoo.org/releases/riscv/autobuilds/current-stage3-rv64_lp64d-systemd-mergedusr/stage3-rv64_lp64d-systemd-mergedusr-20231124T170207Z.tar.xz --directory-prefix=./download
    tar xpvf ./download/stage3-*.tar.xz --xattrs-include='*.*' --numeric-owner -C ./target/rootfs/

== Emerge the base system ==
    riscv64-unknown-linux-gnu-emerge -va1 @system --keep-going

== Customize & configure the rootfs ==
=== Prepare to chroot ===
    cd target
    mount --bind rootfs rootfs
    cd rootfs
    ROOT=$PWD emerge --usepkgonly --oneshot --nodeps qemu
    mount --bind /proc proc
    mount --bind /sys sys
    mount --bind /dev/pts dev/pts
    mkdir -p var/db/repos/gentoo
    mount --bind -o ro /var/db/repos/gentoo var/db/repos/gentoo
    mkdir -p usr/src/linux
    mount --bind -o ro linux usr/src/linux

=== Chroot into the target ===
    chroot $PWD /bin/bash
    source /etc/profile
    export PS1="(chroot) ${PS1}"