mode to use. U-Boot sets up some reasonable values but you can
adjust then with this command.
+Booting Ubuntu
+--------------
+As an example of how to set up your boot flow with U-Boot, here are
+instructions for starting Ubuntu from U-Boot. These instructions have been
+tested on Minnowboard MAX with a SATA driver but are equally applicable on
+other platforms and other media. There are really only four steps and its a
+very simple script, but a more detailed explanation is provided here for
+completeness.
+
+Note: It is possible to set up U-Boot to boot automatically using syslinux.
+It could also use the grub.cfg file (/efi/ubuntu/grub.cfg) to obtain the
+GUID. If you figure these out, please post patches to this README.
+
+Firstly, you will need Ubunutu installed on an available disk. It should be
+possible to make U-Boot start a USB start-up disk but for now let's assume
+that you used another boot loader to install Ubuntu.
+
+Use the U-Boot command line to find the UUID of the partition you want to
+boot. For example our disk is SCSI device 0:
+
+=> part list scsi 0
+
+Partition Map for SCSI device 0 -- Partition Type: EFI
+
+ Part Start LBA End LBA Name
+ Attributes
+ Type GUID
+ Partition GUID
+ 1 0x00000800 0x001007ff ""
+ attrs: 0x0000000000000000
+ type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b
+ guid: 9d02e8e4-4d59-408f-a9b0-fd497bc9291c
+ 2 0x00100800 0x037d8fff ""
+ attrs: 0x0000000000000000
+ type: 0fc63daf-8483-4772-8e79-3d69d8477de4
+ guid: 965c59ee-1822-4326-90d2-b02446050059
+ 3 0x037d9000 0x03ba27ff ""
+ attrs: 0x0000000000000000
+ type: 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f
+ guid: 2c4282bd-1e82-4bcf-a5ff-51dedbf39f17
+ =>
+
+This shows that your SCSI disk has three partitions. The really long hex
+strings are called Globally Unique Identifiers (GUIDs). You can look up the
+'type' ones here [11]. On this disk the first partition is for EFI and is in
+VFAT format (DOS/Windows):
+
+ => fatls scsi 0:1
+ efi/
+
+ 0 file(s), 1 dir(s)
+
+
+Partition 2 is 'Linux filesystem data' so that will be our root disk. It is
+in ext2 format:
+
+ => ext2ls scsi 0:2
+ <DIR> 4096 .
+ <DIR> 4096 ..
+ <DIR> 16384 lost+found
+ <DIR> 4096 boot
+ <DIR> 12288 etc
+ <DIR> 4096 media
+ <DIR> 4096 bin
+ <DIR> 4096 dev
+ <DIR> 4096 home
+ <DIR> 4096 lib
+ <DIR> 4096 lib64
+ <DIR> 4096 mnt
+ <DIR> 4096 opt
+ <DIR> 4096 proc
+ <DIR> 4096 root
+ <DIR> 4096 run
+ <DIR> 12288 sbin
+ <DIR> 4096 srv
+ <DIR> 4096 sys
+ <DIR> 4096 tmp
+ <DIR> 4096 usr
+ <DIR> 4096 var
+ <SYM> 33 initrd.img
+ <SYM> 30 vmlinuz
+ <DIR> 4096 cdrom
+ <SYM> 33 initrd.img.old
+ =>
+
+and if you look in the /boot directory you will see the kernel:
+
+ => ext2ls scsi 0:2 /boot
+ <DIR> 4096 .
+ <DIR> 4096 ..
+ <DIR> 4096 efi
+ <DIR> 4096 grub
+ 3381262 System.map-3.13.0-32-generic
+ 1162712 abi-3.13.0-32-generic
+ 165611 config-3.13.0-32-generic
+ 176500 memtest86+.bin
+ 178176 memtest86+.elf
+ 178680 memtest86+_multiboot.bin
+ 5798112 vmlinuz-3.13.0-32-generic
+ 165762 config-3.13.0-58-generic
+ 1165129 abi-3.13.0-58-generic
+ 5823136 vmlinuz-3.13.0-58-generic
+ 19215259 initrd.img-3.13.0-58-generic
+ 3391763 System.map-3.13.0-58-generic
+ 5825048 vmlinuz-3.13.0-58-generic.efi.signed
+ 28304443 initrd.img-3.13.0-32-generic
+ =>
+
+The 'vmlinuz' files contain a packaged Linux kernel. The format is a kind of
+self-extracting compressed file mixed with some 'setup' configuration data.
+Despite its size (uncompressed it is >10MB) this only includes a basic set of
+device drivers, enough to boot on most hardware types.
+
+The 'initrd' files contain a RAM disk. This is something that can be loaded
+into RAM and will appear to Linux like a disk. Ubuntu uses this to hold lots
+of drivers for whatever hardware you might have. It is loaded before the
+real root disk is accessed.
+
+The numbers after the end of each file are the version. Here it is Linux
+version 3.13. You can find the source code for this in the Linux tree with
+the tag v3.13. The '.0' allows for additional Linux releases to fix problems,
+but normally this is not needed. The '-58' is used by Ubuntu. Each time they
+release a new kernel they increment this number. New Ubuntu versions might
+include kernel patches to fix reported bugs. Stable kernels can exist for
+some years so this number can get quite high.
+
+The '.efi.signed' kernel is signed for EFI's secure boot. U-Boot has its own
+secure boot mechanism - see [12] [13] and cannot read .efi files at present.
+
+To boot Ubuntu from U-Boot the steps are as follows:
+
+1. Set up the boot arguments. Use the GUID for the partition you want to
+boot:
+
+ => setenv bootargs root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro
+
+Here root= tells Linux the location of its root disk. The disk is specified
+by its GUID, using '/dev/disk/by-partuuid/', a Linux path to a 'directory'
+containing all the GUIDs Linux has found. When it starts up, there will be a
+file in that directory with this name in it. It is also possible to use a
+device name here, see later.
+
+2. Load the kernel. Since it is an ext2/4 filesystem we can do:
+
+ => ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic
+
+The address 30000000 is arbitrary, but there seem to be problems with using
+small addresses (sometimes Linux cannot find the ramdisk). This is 48MB into
+the start of RAM (which is at 0 on x86).
+
+3. Load the ramdisk (to 64MB):
+
+ => ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic
+
+4. Start up the kernel. We need to know the size of the ramdisk, but can use
+a variable for that. U-Boot sets 'filesize' to the size of the last file it
+loaded.
+
+ => zboot 03000000 0 04000000 ${filesize}
+
+Type 'help zboot' if you want to see what the arguments are. U-Boot on x86 is
+quite verbose when it boots a kernel. You should see these messages from
+U-Boot:
+
+ Valid Boot Flag
+ Setup Size = 0x00004400
+ Magic signature found
+ Using boot protocol version 2.0c
+ Linux kernel version 3.13.0-58-generic (buildd@allspice) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015
+ Building boot_params at 0x00090000
+ Loading bzImage at address 100000 (5805728 bytes)
+ Magic signature found
+ Initial RAM disk at linear address 0x04000000, size 19215259 bytes
+ Kernel command line: "console=ttyS0,115200 root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro"
+
+ Starting kernel ...
+
+U-Boot prints out some bootstage timing. This is more useful if you put the
+above commands into a script since then it will be faster.
+
+ Timer summary in microseconds:
+ Mark Elapsed Stage
+ 0 0 reset
+ 241,535 241,535 board_init_r
+ 2,421,611 2,180,076 id=64
+ 2,421,790 179 id=65
+ 2,428,215 6,425 main_loop
+ 48,860,584 46,432,369 start_kernel
+
+ Accumulated time:
+ 240,329 ahci
+ 1,422,704 vesa display
+
+Now the kernel actually starts:
+
+ [ 0.000000] Initializing cgroup subsys cpuset
+ [ 0.000000] Initializing cgroup subsys cpu
+ [ 0.000000] Initializing cgroup subsys cpuacct
+ [ 0.000000] Linux version 3.13.0-58-generic (buildd@allspice) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 (Ubuntu 3.13.0-58.97-generic 3.13.11-ckt22)
+ [ 0.000000] Command line: console=ttyS0,115200 root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro
+
+It continues for a long time. Along the way you will see it pick up your
+ramdisk:
+
+ [ 0.000000] RAMDISK: [mem 0x04000000-0x05253fff]
+...
+ [ 0.788540] Trying to unpack rootfs image as initramfs...
+ [ 1.540111] Freeing initrd memory: 18768K (ffff880004000000 - ffff880005254000)
+...
+
+Later it actually starts using it:
+
+ Begin: Running /scripts/local-premount ... done.
+
+You should also see your boot disk turn up:
+
+ [ 4.357243] scsi 1:0:0:0: Direct-Access ATA ADATA SP310 5.2 PQ: 0 ANSI: 5
+ [ 4.366860] sd 1:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB)
+ [ 4.375677] sd 1:0:0:0: Attached scsi generic sg0 type 0
+ [ 4.381859] sd 1:0:0:0: [sda] Write Protect is off
+ [ 4.387452] sd 1:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
+ [ 4.399535] sda: sda1 sda2 sda3
+
+Linux has found the three partitions (sda1-3). Mercifully it doesn't print out
+the GUIDs. In step 1 above we could have used:
+
+ setenv bootargs root=/dev/sda2 ro
+
+instead of the GUID. However if you add another drive to your board the
+numbering may change whereas the GUIDs will not. So if your boot partition
+becomes sdb2, it will still boot. For embedded systems where you just want to
+boot the first disk, you have that option.
+
+The last thing you will see on the console is mention of plymouth (which
+displays the Ubuntu start-up screen) and a lot of 'Starting' messages:
+
+ * Starting Mount filesystems on boot [ OK ]
+
+After a pause you should see a login screen on your display and you are done.
+
+If you want to put this in a script you can use something like this:
+
+ setenv bootargs root=UUID=b2aaf743-0418-4d90-94cc-3e6108d7d968 ro
+ setenv boot zboot 03000000 0 04000000 \${filesize}
+ setenv bootcmd "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; run boot"
+ saveenv
+
+The \ is to tell the shell not to evaluate ${filesize} as part of the setenv
+command.
+
+You will also need to add this to your board configuration file, e.g.
+include/configs/minnowmax.h:
+
+ #define CONFIG_BOOTDELAY 2
+
+Now when you reset your board it wait a few seconds (in case you want to
+interrupt) and then should boot straight into Ubuntu.
+
+You can also bake this behaviour into your build by hard-coding the
+environment variables if you add this to minnowmax.h:
+
+#undef CONFIG_BOOTARGS
+#undef CONFIG_BOOTCOMMAND
+
+#define CONFIG_BOOTARGS \
+ "root=/dev/sda2 ro"
+#define CONFIG_BOOTCOMMAND \
+ "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \
+ "ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \
+ "run boot"
+
+#undef CONFIG_EXTRA_ENV_SETTINGS
+#define CONFIG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}"
+
+
Development Flow
----------------
These notes are for those who want to port U-Boot to a new x86 platform.
[8] http://en.wikipedia.org/wiki/Microcode
[9] http://simplefirmware.org
[10] http://www.intel.com/design/archives/processors/pro/docs/242016.htm
+[11] https://en.wikipedia.org/wiki/GUID_Partition_Table
+[12] http://events.linuxfoundation.org/sites/events/files/slides/chromeos_and_diy_vboot_0.pdf
+[13] http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf
projects / u-boot.git / commitdiff