Let’s try these alternate methods for booting the board
Factory boot
Quickly testing your board with factory kernel image, rootfs
Custom kernel and rootfs on second part of eMMC
If you don’t have a rootfs image initially,this is convenient to test your custom kernel against factory rootfs in eMMC with well defined utilities, For this set the boot parameters as follows
setenv bootargs 'console=ttyO0,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait assuming no SD card is present
Custom kernel and rootfs on second part of SD card.
This is most convenient for frequent updations on rootfs, for this extract the contents of rootfs image into 2nd part of SD card and set the boot params as follows
setenv bootargs 'console=ttyO0,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
Note:- 1.If SD card is connected to the board, SD card partitions are represented as /dev/mmcblk0p1, /dev/mmcblk0p2 and eMMC partitions are represented as /dev/mmcblk1boot, /dev/mmcblk1p2.
2.When there is no SD card is connected, /dev/mmcblk0p1,/dev/mmcblk0p2 represents eMMC partitions.
3.Best way to ensure above device file names is…boot the target once with factory kernel(auto boot) and check the entries in /dev directory.
Loading kernel image, dtb file, initrd.img via TFTP from Host PC
This is convinient for initial testing and eliminating the use of accessories like SD card and card reader.
Ensure TFTP server is installed on host PC, and configure ~/eworkdir/deploy as TFTP root, in which zImage, dtb,rootfs image are available
Connect the target board and Host PC using a LAN cable and assign a suitable ip address to ethernet interface of host PC
ifconfig eth0 192.168.x.y
Stop the autoboot thru minicom to enter u-boot console,and follow these steps to boot the target
setenv ipaddr 192.168.x.z
setenv serverip 192.168.x.y #Choose 192.168.x.y, 192.168.x.z suitably
ping 192.168.x.y
tftp 0x88080000 myrootfs.img #note down the size
tftp 0x82000000 zImage
tftp 0x88000000 am335x-boneblack.dtb
setenv bootargs 'console=ttyO0,115200n8 root=/dev/ram0 rw initrd=0x88080000,<size>'
(or)
setenv bootargs 'console=ttyO0,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
bootz 0x82000000 - 0x88000000
Working with uImage instead of zImage
Even though zImage is accepted by recent u-boot versions and loaded with the help of bootz command,some previous u-boot versions won’t not allow zImage and expect uImage generated by mkimage utility wrapped with LOADADDRESS, and such uImage is loaded by bootm command, Let’s follow these steps to work with uImage
For recent ubuntu distributions(checked on 16.04) mkimage is available through the package u-boot-tools, so you can get it with the following command
sudo apt-get install u-boot-tools
But mkimage utility is not available through package managers of many other distributions,in such distros we need to build the u-boot source code (full build or tools-only) to generate mkimage utility
Download any recent stable version of u-boot from ftp://ftp.denx.de/pub/u-boot/, in the form of u-boot-yyyy.mm.tar.bz2, where yyyy, mm represents year & month of latest release (u-boot-latest.tar.bz2 always link to recent stable version)
Extract the u-boot source tar ball
tar -jxvf u-boot-yyyy.mm.tar.bz2
cd u-boot-yyyy.mm #let’s call it as USRC for current work
make tools-only
cp tools/mkimage /usr/local/bin (or) ln -s $PWD/tools/mkimage /usr/local/bin
Now while building kernel source, after the generation of zImage, let’s run the following step to generate uImage
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- uImage LOADADDR=0x80008000
This step transforms zImage into uImage as follows (just for your reference,no need to run this,you can also notice this command syntax at the end of above step)
mkimage -A arm -O linux -C none -T kernel -a 0x80008000 -e 0x80008000 -n 'Linux-4.x.x-BBB' -d zImage uImage
Now collect the arch/boot/uImage and use accordingly,i.e. using tftp or fatload load the uImage instead of zImage and replace bootz by bootm
bootm 0x82000000 - 0x88000000
Auto boot with custom kernel using uEnv command
Auto boot with boot.scr (TODO)
Note:- we are using factory u-boot loaded in eMMC part1 till now, you may try some steps later to work with your own bootloader.(TODO)