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U-booting Funtoo on the TI AM335x X2 SBC-B2

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Introduction
== Introduction ==
Installing Funtoo to a Raspberry Pi is fun, but there are a lot more boards out there. For example, the carrier boards that hold a DIMM mounted AM335x series cpu. To get this going, we need to use the U-Boot bootloader, some knowledge of serial consolesdevice tree blobs, and a lot of patience.  For this article, we are using this [http://www.goembed.com/index.php/Products/detail/tpid/49 board]. You can read all about it [https://www.dropbox.com/sh/qk4fligwqth7547/AADVvhXGAOxkbqFRKPP8eeSja/SBC335x-B2A?dl=0 here] but the steps depicted here should get you a manufacturer supplied 4.1.8 kernel with a Funtoo stage3 running on it. Possibly. Don't buy it if you don't absolutely need it. There are far better choices.
{{note|When you pick a board, documentation is just as important as hardware features. Without it, you WILL be hunting down someone in Shenzhen to explain why the board refuses to boot (you forgot to ground C8, of course).}}
{{warning|This is kind of a ridiculous exercise, given the author's limited level and the wild idiosyncrasies of board programming, but it may be instructive. It helps me.}}
See http://funtoo.org/Crossdev_Automation for == Making the Environment ==Edit xcompile_variables.sh script to set XC_WORK, XC_LINUX_PREFIX, ARCH, CROSSDEV_TARGET, and environment STAGE3 variables referenced hereto taste. For this board, and we use:* CROSSDEV_TARGET="arm-linux-gnueabihf"* ARCH=arm* STAGE3=funtoo-current/arm-32bit/armv7a_neon_hardfp* STAGE3_CFLAGS="-O2 -pipe -march=armv7-a more complete introduction to the process via a complete install of Funtoo to Raspberry Pi 2 and 3-mfpu=neon -mfloat-abi=hard"* STAGE3_NAME=stage3-latest.tar.xz
{{console|body=
# . xcompile_variables.sh
# mkdir -p $CONFIGS $FIRMWARE $LINUX $UBOOTS $STAGE3S
}}
== Kernel Building Retrieve Sources ==This is an example of using manufacturer supplier scripts for defconfig generation{{console|body=# git clone https://github.com/zhengsjgoembed/335x-b4-uboot.git $XC_UBOOT# git clone https://github.com/zhengsjgoembed/335x-b4.git $XC_KERNEL_SRC# wget https://git.ti.com/ti-cm3-pm-firmware/amx3-cm3/blobs/7c6075f28d9fdd633175cdbd8dc287613ce92e5d/bin/am335x-pm-firmware.bin -O $XC_FIRMWARE/am335x-pm-firmware.bin# wget https://git.ti.com/ti-cm3-pm-firmware/amx3-cm3/blobs/7c6075f28d9fdd633175cdbd8dc287613ce92e5d/bin/am335x-pm-firmware. Don't forget to adjust the make jobs with elf -O $XC_FIRMWARE/am335x-j <N> or just alias make="make pm-j<N>" to copy paste the commands directlyfirmware.elf}}
=== Defconfig Generation =Crossdev ==This is a particular choice of defconfigSee Crossdev_Automation for info on how to get crossdev running on Funtoo.
{{console|body=
# cd $XC_KERNEL_SRC# ARCH=$ARCH CROSS_COMPILE=crossdev -t $CROSSDEV_TARGET ti_config_fragments/defconfig_builder--gcc 4.sh 9.3 -t ti_sdk_am3x_releaseP -v# ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET make ti_sdk_am3x_release_defconfiggcc-config -l [1] arm-linux-gnueabihf-4.9.3 * [2] arm-linux-gnueabihf-5.2.0}} [3] arm-linux-gnueabihf-5.3.0
[4] armv6j-hardfloat-linux-gnueabi-4.8.4 *
[5] armv7a-hardfloat-linux-gnueabi-4.8.4
...<lots of compilers>...
}}
== Kernel Building ==
{{console|body=
# . xcompile_variables# get_kernel_version4.1.18# set_kernel_extraversion = -defconfig && . xcompile_variables.sh# get_kernel_version 4.1.18-defconfig# cd $XC_KERNEL_SRC# alias make="make -j<N>"# cp am335x_b4_deconfig $XC_KERNEL_CONFIG# . xcompile_variablesYour current kernel configs for <XC_LINUX_PREFIX> type builds:Use 4.1.18.kconf as config (y/n)? ySetting XC_KERNEL_OLDCONFIG to /usr/src/fun_kernel/configs/<XC_LINUX_PREFIX>/4.1.18.kconf# cp XC_KERNEL_OLDCONFIG .config# ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET- make uImage zImage modules dtbs modules LOADADDR=0x82000000
}}
== U-Boot Building ==
Notice the use of O=$XC_LINUX_PREFIX to control output. Remove this directory is if you need to clean for a rebuild. DTC is the device tree compiler locationthat permits the use of Device Tree Blobs, an absolutely essential tool for managing the wild forest of ARM processors and base boards. Again, a mysterySee this [http://xillybus.com/tutorials/device-tree-zynq-1 tutorial] on the Device Tree.
{{console|body=
# wget $UBOOT_URL -O $UBOOTS/$UBOOT
# cd $UBOOTS
# mkdir u-boot && tar xf $UBOOT -C u-boot --strip-components 1
# cd $XC_UBOOT
# ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET- make mrproper
== Setup Stage3 ==
We Follow the steps in http://funtoo.org/Crossdev_Automation#Stage3_Configuration but do not set up the boot partion differently. The rest of the steps are the similara software clock. Our board has a hardware clock as well. {{console|body=# sed -i "s/\/dev\/sda1.*/\/dev\/mmcblk0p1 \/boot/uboot vfat defaults 0 2/" $XC_STAGE3S/etc/fstab # mkdir -p $XC_STAGE3S/boot/uboot}}
===Copy Over Kernel Filesand Firmware===
{{console|body=
# cd $XC_KERNEL_SRC
# ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET- INSTALL_MOD_PATH=$XC_STAGE3S INSTALL_MOD_STRIP=1 make modules_install
# ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET- INSTALL_FW_PATH=$XC_STAGE3S make firmware_install# cp $XC_FIRMWARE/* $XC_STAGE3S/lib/firmware# cp arch/arm/boot/zImage $XC_STAGE3S/boot# cp arch/arm/boot/dts/*.dtb $XC_STAGE3S/boot# get_kernel_release() { (cd $XC_KERNEL_SRC ; ARCH=$ARCH CROSS_COMPILE=$CROSSDEV_TARGET- make kernelrelease;) }
# rm $XC_STAGE3S/lib/modules/`get_kernel_release`/{build,source}
}}
===Copy Over U-Boot Files===
Leave a blank line at the end of the u-boot config. For some reason or other.
{{console|body=
# cp $XC_UBOOT/$XC_LINUX_PREFIX/{MLO,u-boot.img,u-boot.bin} $XC_STAGE3S/boot/uboot# cp arch/arm/boot/uImage $XC_STAGE3S/boot/uboot# echo "bootargs=console=ttyO0,115200n8 root=/dev/mmcblk0p2 mem=128M rootwaitbootcmd=mmc rescan; fatload mmc 0 0x82000000 uImage; bootm 0x82000000uenvcmd=boot" > $XC_STAGE3S/boot/uboot/uEnv.txt
}}
# parted -s /dev/<your_dev> set 1 boot on
# parted -s /dev/<your_dev> unit cyl mkpart primary ext2 -- 9 -2
# mkfs.vfat -F 32 -n boot /dev/<your_dev>1
# mkfs.ext4 -L rootfs /dev/<your_dev>2
}}
# mkdir -p /mnt/funtoo
# mount /dev/<your_dev>2 /mnt/funtoo
# mkdir -p /mnt/funtoo/boot/uboot# mount /dev/<your_dev>1 /mnt/funtoo/boot/uboot
# rsync -avz --exclude "usr/portage/*" $XC_STAGE3S/{boot,bin,etc,home,lib,mnt,opt,root,run,sbin,srv,tmp,usr,var,dev} /mnt/funtoo
# mkdir -p /mnt/funtoo/{proc,sys}
# umount -R /mnt/funtoo
}}
 
Reboot! Moment of truth: do you really know what you are doing?
 
{{tip|Once you get the board up and sshd running on it, then use rsync -e "ssh" $XC_STAGE3S/{boot,lib} <board_ip>:/ to do the kernel hacking. How long can you keep it up?}}
 
== If It Boots... ==
=== Device Tree Fun ===
This is important. In embedded world we need to always handle the relationship between the cpu and baseboard that carries it. We can use the u-boot shell to find this out.
 
{{console|body=
=> bdinfo
arch_number = 0x00000F8C
boot_params = 0x10000100
DRAM bank = 0x00000000
-> start = 0x10000000
-> size = 0x80000000
eth0name = FEC
ethaddr = (not set)
current eth = FEC
ip_addr = <NULL>
baudrate = 115200 bps
TLB addr = 0x8FFF0000
relocaddr = 0x8FF4A000
reloc off = 0x7874A000
irq_sp = 0x8EF47EA0
sp start = 0x8EF47E90
FB base = 0x8EF4B7C0
}}
 
This structure is extremely useful in finding an appropriate device tree file so that the cpu can talk to the registers on the hardware and engage with interupts. It's pretty cool.
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