Run Linaro Ubuntu Desktop on ZED AP SoC Board – Step-By-Step Guide

ZED board is currently shipped with Linux kernel with a RAM disk file systems.
However, it is fairly simple to get a desktop version of Linaro Ubuntu running on it.
In this blog, I will give you step-by-step instructions with pictures to get Linaro Ubuntu running on your ZED board with the kernel image in the SD card.

Things You Need

A. A Linux Machine

You need a Linux machine to format disks, copy files, etc. You cannot do these under Windows because Windows does not support EXT filesystem, and cannot understand special files (e.g. device files, link files, etc.) which only exists for Unix-like systems. Any Linux distributions, such as Fedora, CentOS, RHEL, Ubuntu, ArchLinux, etc.) can satisfy our needs.

B. Linaro Ubuntu File System Image

You can view Linaro Ubuntu as a Ubuntu distribution specifically for ARM-based processors. You can obtained the file system image from linaro 12.09. The file system is about 500ish MB. The current built is called: linaro-precise-ubuntu-desktop-20120923-436.tar.gz

C. SD Card Image (containing Kernel, BOOT.BIN, etc.)

Before we move on to modify the SD card, it is recommended to store the files on the SD card to some place. However, you can also obtain those files from Digilent Website: Out-of-Box SD Card Image .

Idea for Running Desktop

To run desktop linux, you just need to swap the file system from RAMDISK to linaro file system image. The ramdisk gets loaded up into the SDRAM by bootloader, and the memory address is passed to kernel via boot args (defined in device tree file: devicetree_ramdisk.dtb). However, the file system of Ubuntu is above 500MB. So, we cannot load it as the way we deal with RAMDISK (which is usually around 4~8 MB). As a result, we are going to make a second partition on SD card (3GB), make a root filesystem on it, and point it as the root filesystem in dtb file.

Step-by-Step Instructions

A. Repartition the SD Card

1. Plug in your SD Card to your Linux machine. Some distribution will automatically mount the partition on SD Card. So, you need to umount the automounted partitions first, before we repartition the disk.

On my computer, when I insert the SD card, the device node created for the SD card on my machine is /dev/sdd:

[ ~]$ df 
Filesystem 1K-blocks Used Available Use% Mounted on
470166952 316061992 130221800 71% /
tmpfs 3988440 976 3987464 1% /dev/shm
/dev/sda1 495844 65557 404687 14% /boot
/dev/sdd1 3862528 10268 3852260 1% /media/ZED_BOOT

Umount the pre-mounted SD Card Partition:

[ ~]$ sudo umount /media/ZED_BOOT/
[ ~]$ df
Filesystem 1K-blocks Used Available Use% Mounted on
470166952 316062016 130221776 71% /
tmpfs 3988440 976 3987464 1% /dev/shm
/dev/sda1 495844 65557 404687 14% /boot
[ ~]$

2. Now we will delete the original 4G FAT Partition and create two partitions: first one is 1GB FAT for booting files, and second one is 3GB EXT4 for root file system. The partition utility we will use is fdisk.

Open the SD card device using fdisk, and use command p to print current partition table on SD card.

[ ~]$ sudo fdisk /dev/sdd
[sudo] password for

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').

Command (m for help): p

Disk /dev/sdd: 3965 MB, 3965190144 bytes
228 heads, 2 sectors/track, 16983 cylinders
Units = cylinders of 456 * 512 = 233472 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00047708

Device Boot Start End Blocks Id System
/dev/sdd1 1 16978 3870720 b W95 FAT32

Type command d to delete the partition. As there is only one partition on SD card, it will be deleted automatically.

Command (m for help): d
Selected partition 1

Command (m for help): p

Disk /dev/sdd: 3965 MB, 3965190144 bytes
228 heads, 2 sectors/track, 16983 cylinders
Units = cylinders of 456 * 512 = 233472 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00047708

Device Boot Start End Blocks Id System

Now it’s time for us to create new partitions. We will create
a. A primary partition, Partition Number 1, Start from first Cylinder, Size of 1GB;
b. A primary partition, Partition Number 2, Start from next available Cylinder, Take rest of the available space on SD Card.
Command n stands for “New Partitions”.

Command (m for help): n
Command action
e extended
p primary partition (1-4)
Partition number (1-4): 1
First cylinder (1-16983, default 1): 1
Last cylinder, +cylinders or +size{K,M,G} (1-16983, default 16983): +1G

Command (m for help): p

Disk /dev/sdd: 3965 MB, 3965190144 bytes
228 heads, 2 sectors/track, 16983 cylinders
Units = cylinders of 456 * 512 = 233472 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00047708

Device Boot Start End Blocks Id System
/dev/sdd1 1 4600 1048799 83 Linux

Command (m for help): n
Command action
e extended
p primary partition (1-4)
Partition number (1-4): 2
First cylinder (4601-16983, default 4601):
Using default value 4601
Last cylinder, +cylinders or +size{K,M,G} (4601-16983, default 16983):
Using default value 16983

Command (m for help): p

Disk /dev/sdd: 3965 MB, 3965190144 bytes
228 heads, 2 sectors/track, 16983 cylinders
Units = cylinders of 456 * 512 = 233472 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00047708

Device Boot Start End Blocks Id System
/dev/sdd1 1 4600 1048799 83 Linux
/dev/sdd2 4601 16983 2823324 83 Linux

So far, we have finished creating two new partitions. We write our changes back to SD card using command w and fdisk will quit automatically after disk is sychronized.

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
[ ~]$
B. Creating File Systems

Next Step is to create file systems. We need to format the first partition to FAT with label “ZED_BOOT”, and Second one EXT4 with label “ROOT_FS”. The utility we use for formatting partitions is makefs.

[ ~]$ sudo mkfs -t vfat -n ZED_BOOT /dev/sdd1
mkfs.vfat 3.0.9 (31 Jan 2010)
[ ~]$ sudo mkfs -t ext4 -L ROOT_FS /dev/sdd2
mke2fs 1.41.12 (17-May-2010)
Filesystem label=ROOT_FS
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
176704 inodes, 705831 blocks
35291 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=725614592
22 block groups
32768 blocks per group, 32768 fragments per group
8032 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912

Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
[ ~]$

Now, unplug the SD Card from your computer and plug it in again. In most Linux distributions, both partitions will be mounted to /media/ZED_BOOT and /media/ROOT_FS automatically. If not, you need to create two folders manually and mount them manually.

C. Creating Linaro Ubuntu Root Filesystem

Personally, I would like to create a folder named linaro under /tmp and copy the zipped linaro image there.

[ ~]$ mkdir -p /tmp/linaro
[ ~]$ sudo cp /home/ /tmp/linaro/
[ ~]$ cd /tmp/linaro/
[ linaro]$ ls
[ linaro]$

Unpack the disk image using tar. (Part of the log is omitted for brevity).

[ linaro]$ tar zxvf linaro-precise-ubuntu-desktop-20120923-436.tar.gz
[ linaro]$ ls
binary linaro-precise-ubuntu-desktop-20120923-436.tar.gz

After unpacking the disk image, the root filesystem lies at /tmp/linaro/binary/boot/filesystem.dir. So the next step to do is to copy the root filesystem into the second partition of our SD Card, mounted already to /media/ROOT_FS. A lot of files in the root filesystem are special files with special attributes, I would recommend to use rsync to do the copy, which keeps the attibutes for every file. It takes a while to copy the file to SD card, basically depended on your SD card speed. (Part of the log is omitted for brevity).

[ binary]$ cd binary/boot/filesystem.dir/
[ filesystem.dir]$ pwd
[ filesystem.dir]$ sudo rsync -a --progress ./ /media/ROOT_FS/
sending incremental file list
37 100% 0.00kB/s 0:00:00 (xfer#1, to-check=1039/1061)
36 100% 0.78kB/s 0:00:00 (xfer#2, to-check=1152/1175)
605140 100% 12.02MB/s 0:00:00 (xfer#4, to-check=1150/1175)
22112 100% 449.87kB/s 0:00:00 (xfer#5, to-check=1149/1175)

sent 1331510996 bytes received 1327420 bytes 3738677.18 bytes/sec
total size is 1325555569 speedup is 0.99
[ filesystem.dir]$

To make sure all the files have been sychronized to SD card, we need to unmount the /media/ROOT_FS before we unplug the SD card. It may take several minutes to get everything synchronized onto SD Card.

[ filesystem.dir]$ sudo umount /media/ROOT_FS/
D. Getting images files back to FAT partition

We are almost done. To boot up the whole system, we need to get the original SD card files back to FAT partition. As mentioned before, we can get them from the Out-of-Box Design available on Digilent Website.

[ ~]$ cp ~/Downloads/ZedBoard_OOB_Design/sd_image/* /media/ZED_BOOT/ -rfv
`/home/' -> `/media/ZED_BOOT/BOOT.BIN'
`/home/' -> `/media/ZED_BOOT/devicetree_ramdisk.dtb'
`/home/' -> `/media/ZED_BOOT/ramdisk8M.image.gz'
`/home/' -> `/media/ZED_BOOT/README'
`/home/' -> `/media/ZED_BOOT/zImage'
[ ~]$

You need to change the bootargs defined in the DTB to let the kernel use the second partition of SD card as root file system. To make your life easier, I precompiled a dtb file for you available at: devicetree_linaro.dtb

[ ~]$ cp ~/Downloads/* /media/ZED_BOOT/devicetree_linaro.dtb -rfv
[ ~]$
E. Boot up Your Desktop Ubuntu

Insert your SD Card into your ZED Board, connect a monitor to the ZED Board with an HDMI cable, connect the UART port to your computer, open a hyper-terminal for it (115200, 8 bit, 1 stop bit, no parity, no flow control) and boot it up. However, automatically, the boot loader (U-Boot) will still look for ramdisk by default. So, you need to stop the autoboot by pressing a key during the 3-second count down, and type command run sdboot_linaro to boot Linaro Ubuntu Desktop up.

U-Boot 2012.04.01-00297-gc319bf9-dirty (Sep 13 2012 - 09:30:49)

DRAM: 512 MiB
WARNING: Caches not enabled
Using default environment

In: serial
Out: serial
Err: serial
Net: zynq_gem
Hit any key to stop autoboot: 0
zed-boot> run sdboot_linaro

Embedded Linux – Memory Management Line by line [1]– Intro to MMU

For embedded system, memory management varies from system to system, as you have your custom address space and custom peripheral devices and memory chips. Sometime, the porting of kernel may fail if the memory management is not carefully handled.

Years ago, uclinux was well-known as a linux operating system without MMU, which is more suitable for embedded systems back at that time. As FPGA has become more and more powerful, embedded OS can support MMU now. And for Linux running on Xilinx FPGA with microblaze or PPC, the MMU is required, as said in the documentation.

In this blog series, I am going to tell the story about memory management of Linux OS line by line. The story begins by introducing the MMU of microblaze.

MMU of Microblaze on Xilinx FPGA\

Memory Management Unit (MMU) is a piece of hardware, which bonded closely with CPU (microblaze/PPC here) to provide memory management functionality for softwares, especially operating systems.

MMU can function in two modes:

1. Real Mode: effective address are used to access physical memory directly.

2. Virtual Mode: effective address are translated into physical address to access physical memory by the virtual-memory management hardware in microblaze.

The mode is controlled by the 18th bit (VM) of rmsr (Machine Status Register), as shown in fig. 1.


                                 fig. 1 Machine Status Register


At the very beginning, the MMU runs in real mode, as the reset value of VM is 0. After OS properly set the first several entry in TLB (Translation Look-aside Buffer), the MMU will switch into Virtual Mode.

In virtual mode, whenever an address is requested, it goes through the following procedure:


To understand this procedure, we need to know so-called Translation Look-aside Buffer (TLB). TLB can be viewed as a cache for address translation. The translation between virtual address and physical address in virtual mode is done via a kind of mechanism called 2-level page table translation. In microblaze, the translation goes as follows:


There are certain addresses that are frequently accessed, the translation is stored in TLB, the same we do for data cache. If the requested data is not found in TLB, a TLB miss (similar as cache miss) is generated, followed by the page table translation and TLB update operation.

There are four registers used for accessing TLB from software: TLBLO, TLBHI, TLBX, and TLBSX.

TLBLO: Translation Look-Aside Buffer Low Register

TLBHI: Translation Look-Aside Buffer High Register

TLBX: Translation Look-Aside Buffer Index Register

TLBSX: Translation Look-Aside Buffer Search Index Register

All these registers are accessed via MFS and MTS instructions.

Access TLB Entries

First of all, we need to know the TLB entry structure. A TLB entry can be accessed via TLBLO and TLBHI registers, with an index set at TLBX.


RPN (Real Page Number or Physical Page Number) is used to form physical address. Depending on the value of page size, certain bits of RPN are not used in physical address.

TAG (TLB-entry tag) is compared with the virtual memory address under control of SIZE.

SIZE (page Size) specifies page size.

There are 64 entries in the unified TLB in microblaze MMU architecture. So the INDEX field (bit 26 to 31, as shown below) of TLBX register is used as index of MMU entries. The field is also updated when TLBSX register is written with a virtual address and the virtual address is found in TLB entries.


Software can read and write unified TLB entries by using the TLBX register index (numbered 0 to 63) corresponding to one of the 64 entries in the TLB. The tag and data portions are read and written separately, so software must execute two MFS or MTS instructions to completely access an entry. The TLB is searched for a specific translation using the TLBSX register. TLBSX locates a translation using an effective address and loads the corresponding UTLB index into the TLBX register.


All the above are the story about MMU architecture of microblaze. You may refer to xilinx document: MicroBlaze Processor Reference Guide for more detail explanation on microblaze and its instructions. The figures and information in this blog comes from the document directly. Linux kernel set up memory page mapping in arch/microblaze/head.S. I am going to talk about the codes in head.S in next blog in this series.

WordPress Tags: physical address,virtual address,TLB,Xilinx,FPGA,microblaze,MMU,Linux,Memory Management