Linux on ARM: xz kernel decompression benchmarks

I recently managed to find time to clean up and submit my patches for xz kernel compression support on ARM, which I started working on back in November, during my flight to Linaro Connect. However, it was too late as Russell King, the ARM Linux maintainer, alreadyaccepted a similar patch, about 3 weeks before my submission. The lesson I learned was that checking a git tree is not always sufficient. I should have checked the mailing list archives too.

The good news is that xz kernel compression support should be available in Linux 3.4 in a few months from now. xz is a compression format based on the LZMA2 compression algorithm. It can be considered as the successor of lzma, and achieves even better compression ratios!

Before submitting my patches, I ran a few benchmarks on my own implementation. As the decompressing code is the same, the results should be the same as if I had used the patches that are going upstream.

Benchmark methodology

For both boards I tested, I used the same pre 3.3 Linux kernel from Linus Torvalds’ mainline git tree. I also used the U-boot bootloader in both cases.

I used the very useful grabserial script from Tim Bird. This utility reads messages coming out of the serial line, and adds timestamps to each line it receives. This allow to measure time from the earliest power on stages, and doesn’t slow down the target system by adding instrumentation to it.

Our benchmarks just measure the time for the bootloader to copy the kernel to RAM, and then the time taken by the kernel to uncompress itself.

  • Loading time is measured between “reading uImage” and “OK” (right before “Starting kernel”) in the bootloader messages.
  • Compression time measured between “Uncompressing Linux” and “done”:
    ~/bin/grabserial -v -d /dev/ttyUSB0 -e 15 -t -m "Uncompressing Linux" -i "done," > booting-lzo.log

Benchmarks on OMAP4 Panda

The Panda board has a fast dual Cortex A9 CPU (OMAP 4430) running at 1 GHz. The standard way to boot this board is from an MMC/SD card. Unfortunately, the MMC/SD interface of the board is rather slow.

In this case, we have a fast CPU, but with rather slow storage. Therefore, the time taken to copy the kernel from storage to RAM is expected to have a significant impact on boot time.

This case typically represents todays multimedia and mobile devices such as phones, media players and tablets.

Compression Size Loading time Uncompressing time Total time
gzip 3355768 2.213376 0.501500 2.714876
lzma 2488144 1.647410 1.399552 3.046962
xz 2366192 1.566978 1.299516 2.866494
lzo 3697840 2.471497 0.160596 2.632093
None 6965644 4.626749 0 4.626749

Results on Calao Systems USB-A9263 (AT91)

The USB-A9263 board from Calao Systems has a cheaper and much slower AT91SAM9263 CPU running at 200 MHz.

Here we are booting from NAND flash, which is the fastest way to boot a kernel on this board. Note that we are using the nboot command from U-boot, which guarantees that we just copy the number of bytes specified in the uImage header.

In this case, we have a slow CPU with slow storage. Therefore, we expect both the kernel size and the decompression algorithm to have a major impact on boot time.

This case is a typical example of industrial systems (AT91SAM9263 is still very popular in such applications, as we can see from customer requests), booting from NAND storage operating with a 200 to 400 MHz CPU.

Compression Size Loading time Uncompressing time Total time
gzip 2386936 5.843289 0.935495 6.778784
lzma 1794344 4.465542 6.513644 10.979186
xz 1725360 4.308605 4.816191 9.124796
lzo 2608624 6.351539 0.447336 6.798875
None 4647908 11.080560 0 11.080560

Lessons learned

Here’s what we learned from these benchmarks:

  • lzo is still the best solution for minimum boot time. Remember, lzo kernel compression was merged by Bootlin.
  • xz is always better than lzma, both in terms of image size. Therefore, there’s no reason to stick to lzma compression if you used it.
  • Because of their heavy CPU usage, lzma and xz remain pretty bad in terms of boot time, on most types of storage devices. On systems with a fast CPU, and very slow storage though, xz should be the best solution
  • On systems with a fast CPU, like the Panda board, boot time with xz is actually pretty close to lzo, and therefore can be a very interesting compromise between kernel size and boot time.
  • Using a kernel image without compression is rarely a worthy solution, except in systems with a very slow CPU. This is the case of CPUs emulated on an FPGA (typically during chip development, before silicon is available). In this particular case, copying to memory is directly done by the emulator, and we just need CPU cycles to start the kernel.

Building a small Debian root filesystem with Multistrap

There are several ways to build a root filesystem for an embedded Linux system: Buildroot and Open Embedded are the usual solutions to do this. They allow to fine tune the contents of your filesystem. The drawback is, in both cases, that you need to build everything from sources and this can take from tens of minutes to several hours.

Sometimes you don’t need all this flexibility and you just want to have a ready-to-use root filesystem, to which you just add a few extra programs. In this case using a distribution is a good solution. So let’s see what we need:

  • A binary distribution
  • Available on several architectures
  • Ability to generate a “small” root filesystem
  • A large choice of packages

Oh, I think it is a pretty good description of Debian!

Emdebian is a project to adapt Debian to embedded devices. A good description from the Debian wiki is:

“In short, what EmDebian does is wrap around the regular Debian package building tools to provide a more fine grained control over package selection, size, dependencies and content to enable creation of very small and efficient Debian packages for use on naturally resource limited embedded targets.”

And so, pretty recently (2009), Emdebian released Multistrap which is similar to Debootstrap but more appropriate for embedded devices. It seems better by the way it builds a system:

It works in a completely different way by simply using apt and dpkg, rather than avoiding to use them, which is how Debootstrap works.

And also more appropriate by its goals:

It is focused on producing rootfs images for devices, as opposed to chroots for existing machines

Practical case: build a root filesystem for the USB A9263 board from Calao Systems (arm926ejs based board).

A drawback of Multistrap is its limitation to Debian, but in fact it is also usable on any distribution based on Debian. In our case, we ran it on an Ubuntu 10.04 system.

First, let’s install Multistrap:

$sudo apt-get install multistrap dpkg-dev

Multistrap needs a config file. For our needs we just use the example one given by Embedian. Let’s name it multistrap.conf:

[General]
noauth=true
unpack=true
debootstrap=Grip
aptsources=Grip

[Grip]
# space separated package list
source=http://www.emdebian.org/grip
suite=lenny

Grip is the name of the lightweight Debian distro built by Emdebian.

Now we can run Multistrap:

$ multistrap -a armel -d $PWD/RFS -f multistrap.conf
em_multistrap 0.0.8 using multistrap.conf
Using foreign architecture: armel
em_multistrap building armel multistrap on 'amd64'
INF: Setting ./lib64 -> ./lib symbolic link.
Getting package lists: apt-get  -o Apt::Architecture=armel -o Apt::Get::AllowUnauthenticated=true -o Apt::Get::Download-Only=true -o Apt::Install-Recommends=false -o Dir=/home/mike/celf/multistrap/RFS/ -o Dir::Etc=/home/mike/celf/multistrap/RFS/etc/apt/ -o Dir::Etc::SourceList=/home/mike/celf/multistrap/RFS/etc/apt/sources.list.d/multistrap.sources.list -o Dir::State=/home/mike/celf/multistrap/RFS/var/lib/apt/ -o Dir::State::Status=/home/mike/celf/multistrap/RFS/var/lib/dpkg/status -o Dir::Cache=/home/mike/celf/multistrap/RFS/var/cache/apt/ update
Get:1 http://www.emdebian.org lenny Release.gpg [197B]
Ign http://www.emdebian.org/grip/ lenny/main Translation-en_US
Get:2 http://www.emdebian.org lenny Release [21.4kB]
Ign http://www.emdebian.org lenny Release
Ign http://www.emdebian.org lenny/main Packages
Ign http://www.emdebian.org lenny/main Sources
Ign http://www.emdebian.org lenny/main Packages
Ign http://www.emdebian.org lenny/main Sources
Get:3 http://www.emdebian.org lenny/main Packages [293kB]
Get:4 http://www.emdebian.org lenny/main Sources [351kB]
Fetched 665kB in 0s (6,280kB/s)                     
Reading package lists... Done
W: GPG error: http://www.emdebian.org lenny Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B5B7720097BB3B58
W: Duplicate sources.list entry http://www.emdebian.org/grip/ lenny/main Packages (/home/mike/celf/multistrap/RFS/var/lib/apt/lists/www.emdebian.org_grip_dists_lenny_main_binary-armel_Packages)
Use of uninitialized value within %packages in join or string at /usr/sbin/em_multistrap line 294.
Use of uninitialized value within %keyrings in join or string at /usr/sbin/em_multistrap line 296.
apt-get -y  -o Apt::Architecture=armel -o Apt::Get::AllowUnauthenticated=true -o Apt::Get::Download-Only=true -o Apt::Install-Recommends=false -o Dir=/home/mike/celf/multistrap/RFS/ -o Dir::Etc=/home/mike/celf/multistrap/RFS/etc/apt/ -o Dir::Etc::SourceList=/home/mike/celf/multistrap/RFS/etc/apt/sources.list.d/multistrap.sources.list -o Dir::State=/home/mike/celf/multistrap/RFS/var/lib/apt/ -o Dir::State::Status=/home/mike/celf/multistrap/RFS/var/lib/dpkg/status -o Dir::Cache=/home/mike/celf/multistrap/RFS/var/cache/apt/ install balloon3-config base-files base-passwd bash bsdutils coreutils debianutils diff dpkg e2fslibs e2fsprogs findutils gcc-4.3-base grep grip-config gzip hostname initscripts libacl1 libattr1 libblkid1 libc6 libcap1 libcomerr2 libdevmapper1.02.1 libgcc1 liblocale-gettext-perl libncurses5 libpam-modules libpam-runtime libpam0g libselinux1 libsepol1 libslang2 libss2 libstdc++6 libtext-charwidth-perl libtext-iconv-perl libtext-wrapi18n-perl libuuid1 libvolume-id0 login lsb-base makedev mawk mktemp mount ncurses-base ncurses-bin passwd perl-base procps sed sysv-rc sysvinit sysvinit-utils tar tzdata util-linux zlib1g
Reading package lists... Done
Building dependency tree... Done
The following extra packages will be installed:
  apt debconf debconf-i18n debian-archive-keyring dhcp3-client dhcp3-common gnupg gpgv ifupdown libbz2-1.0 libdb4.6 libncursesw5 libnewt0.52 libpopt0
  libreadline5 libssl0.9.8 libusb-0.1-4 lzma module-init-tools nano net-tools netbase ntpdate readline-common udev wget whiptail
The following NEW packages will be installed:
  apt balloon3-config base-files base-passwd bash bsdutils coreutils debconf debconf-i18n debian-archive-keyring debianutils dhcp3-client dhcp3-common diff
  dpkg e2fslibs e2fsprogs findutils gcc-4.3-base gnupg gpgv grep grip-config gzip hostname ifupdown initscripts libacl1 libattr1 libblkid1 libbz2-1.0 libc6
  libcap1 libcomerr2 libdb4.6 libdevmapper1.02.1 libgcc1 liblocale-gettext-perl libncurses5 libncursesw5 libnewt0.52 libpam-modules libpam-runtime libpam0g
  libpopt0 libreadline5 libselinux1 libsepol1 libslang2 libss2 libssl0.9.8 libstdc++6 libtext-charwidth-perl libtext-iconv-perl libtext-wrapi18n-perl
  libusb-0.1-4 libuuid1 libvolume-id0 login lsb-base lzma makedev mawk mktemp module-init-tools mount nano ncurses-base ncurses-bin net-tools netbase
  ntpdate passwd perl-base procps readline-common sed sysv-rc sysvinit sysvinit-utils tar tzdata udev util-linux wget whiptail zlib1g
0 upgraded, 87 newly installed, 0 to remove and 0 not upgraded.
Need to get 15.4MB of archives.
After this operation, 48.4MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  libstdc++6 libbz2-1.0 readline-common libncurses5 libreadline5 libusb-0.1-4 zlib1g gpgv gnupg debian-archive-keyring apt debianutils dhcp3-common
  libattr1 libacl1 libselinux1 coreutils lzma dpkg perl-base liblocale-gettext-perl libtext-iconv-perl libtext-charwidth-perl libtext-wrapi18n-perl
  debconf-i18n debconf dhcp3-client sed ncurses-bin lsb-base module-init-tools libssl0.9.8 wget hostname net-tools ifupdown mawk libncursesw5 nano netbase
  libcap1 ntpdate libpam-runtime libpam0g libdb4.6 libpam-modules passwd libvolume-id0 udev libslang2 libnewt0.52 libpopt0 whiptail grip-config
  gcc-4.3-base libgcc1 libc6 base-passwd base-files bash diff libcomerr2 e2fslibs libuuid1 libblkid1 libss2 e2fsprogs findutils grep gzip login mktemp
  mount libsepol1 sysvinit-utils initscripts sysv-rc sysvinit tar tzdata util-linux balloon3-config bsdutils libdevmapper1.02.1 makedev ncurses-base procps
Authentication warning overridden.
Get:1 http://www.emdebian.org/grip/ lenny/main libstdc++6 4.3.2-1.1em1 [268kB]
Get:2 http://www.emdebian.org/grip/ lenny/main libbz2-1.0 1.0.5-1em1 [37.2kB]
Get:3 http://www.emdebian.org/grip/ lenny/main readline-common 5.2-3.1em1 [3,202B]
Get:4 http://www.emdebian.org/grip/ lenny/main libncurses5 5.7+20081213-1em1 [165kB]
Get:5 http://www.emdebian.org/grip/ lenny/main libreadline5 5.2-3.1em1 [108kB]
Get:6 http://www.emdebian.org/grip/ lenny/main libusb-0.1-4 2:0.1.12-13em1 [13.7kB]
Get:7 http://www.emdebian.org/grip/ lenny/main zlib1g 1:1.2.3.3.dfsg-12em1 [48.1kB]
Get:8 http://www.emdebian.org/grip/ lenny/main gpgv 1.4.9-3+lenny1em1 [139kB]
Get:9 http://www.emdebian.org/grip/ lenny/main gnupg 1.4.9-3+lenny1em1 [533kB]
Get:10 http://www.emdebian.org/grip/ lenny/main debian-archive-keyring 2010.08.28~lenny1em1 [17.9kB]
Get:11 http://www.emdebian.org/grip/ lenny/main apt 0.7.20.2+lenny2em1 [514kB]
Get:12 http://www.emdebian.org/grip/ lenny/main debianutils 2.30em1 [23.4kB]
Get:13 http://www.emdebian.org/grip/ lenny/main dhcp3-common 3.1.1-6+lenny4em1 [157kB]
Get:14 http://www.emdebian.org/grip/ lenny/main libattr1 1:2.4.43-2em1 [7,706B]
Get:15 http://www.emdebian.org/grip/ lenny/main libacl1 2.2.47-2em1 [14.0kB]
Get:16 http://www.emdebian.org/grip/ lenny/main libselinux1 2.0.65-5em1 [50.0kB]
Get:17 http://www.emdebian.org/grip/ lenny/main coreutils 6.10-6em1 [1,162kB]
Get:18 http://www.emdebian.org/grip/ lenny/main lzma 4.43-14em1 [51.0kB]
Get:19 http://www.emdebian.org/grip/ lenny/main dpkg 1.14.29em1 [405kB]
Get:20 http://www.emdebian.org/grip/ lenny/main perl-base 5.10.0-19lenny2em1 [905kB]
Get:21 http://www.emdebian.org/grip/ lenny/main liblocale-gettext-perl 1.05-4em1 [11.0kB]
Get:22 http://www.emdebian.org/grip/ lenny/main libtext-iconv-perl 1.7-1+b1em1 [11.2kB]
Get:23 http://www.emdebian.org/grip/ lenny/main libtext-charwidth-perl 0.04-5+b1em1 [6,656B]
Get:24 http://www.emdebian.org/grip/ lenny/main libtext-wrapi18n-perl 0.06-6em1 [4,444B]
Get:25 http://www.emdebian.org/grip/ lenny/main debconf-i18n 1.5.24em1 [2,882B]
Get:26 http://www.emdebian.org/grip/ lenny/main debconf 1.5.24em1 [110kB]
Get:27 http://www.emdebian.org/grip/ lenny/main dhcp3-client 3.1.1-6+lenny4em1 [185kB]
Get:28 http://www.emdebian.org/grip/ lenny/main sed 4.1.5-6em1 [23.8kB]
Get:29 http://www.emdebian.org/grip/ lenny/main ncurses-bin 5.7+20081213-1em1 [70.8kB]
Get:30 http://www.emdebian.org/grip/ lenny/main lsb-base 3.2-20em1 [5,888B]
Get:31 http://www.emdebian.org/grip/ lenny/main module-init-tools 3.4-1em1 [44.5kB]
Get:32 http://www.emdebian.org/grip/ lenny/main libssl0.9.8 0.9.8g-15+lenny8em1 [713kB]
Get:33 http://www.emdebian.org/grip/ lenny/main wget 1.11.4-2+lenny2em1 [116kB]
Get:34 http://www.emdebian.org/grip/ lenny/main hostname 2.95em1 [5,808B]
Get:35 http://www.emdebian.org/grip/ lenny/main net-tools 1.60-22em1 [156kB]
Get:36 http://www.emdebian.org/grip/ lenny/main ifupdown 0.6.8+nmu1em1 [18.9kB]
Get:37 http://www.emdebian.org/grip/ lenny/main mawk 1.3.3-11.1em1 [51.2kB]
Get:38 http://www.emdebian.org/grip/ lenny/main libncursesw5 5.7+20081213-1em1 [187kB]
Get:39 http://www.emdebian.org/grip/ lenny/main nano 2.0.7-5em1 [83.6kB]
Get:40 http://www.emdebian.org/grip/ lenny/main netbase 4.34em1 [11.6kB]
Get:41 http://www.emdebian.org/grip/ lenny/main libcap1 1:1.10-14em1 [7,574B]
Get:42 http://www.emdebian.org/grip/ lenny/main ntpdate 1:4.2.4p4+dfsg-8lenny3em1 [36.1kB]
Get:43 http://www.emdebian.org/grip/ lenny/main libpam-runtime 1.0.1-5+lenny1em1 [7,786B]
Get:44 http://www.emdebian.org/grip/ lenny/main libpam0g 1.0.1-5+lenny1em1 [41.0kB]
Get:45 http://www.emdebian.org/grip/ lenny/main libdb4.6 4.6.21-11em1 [531kB]
Get:46 http://www.emdebian.org/grip/ lenny/main libpam-modules 1.0.1-5+lenny1em1 [160kB]
Get:47 http://www.emdebian.org/grip/ lenny/main passwd 1:4.1.1-6+lenny1em1 [267kB]
Get:48 http://www.emdebian.org/grip/ lenny/main libvolume-id0 0.125-7+lenny3em1 [18.2kB]
Get:49 http://www.emdebian.org/grip/ lenny/main udev 0.125-7+lenny3em1 [145kB]
Get:50 http://www.emdebian.org/grip/ lenny/main libslang2 2.1.3-3em1 [266kB]
Get:51 http://www.emdebian.org/grip/ lenny/main libnewt0.52 0.52.2-11.3+lenny1em1 [36.7kB]
Get:52 http://www.emdebian.org/grip/ lenny/main libpopt0 1.14-4em1 [22.3kB]
Get:53 http://www.emdebian.org/grip/ lenny/main whiptail 0.52.2-11.3+lenny1em1 [11.7kB]
Get:54 http://www.emdebian.org/grip/ lenny/main grip-config 0.1.2em1 [11.5kB]
Get:55 http://www.emdebian.org/grip/ lenny/main gcc-4.3-base 4.3.2-1.1em1 [5,496B]
Get:56 http://www.emdebian.org/grip/ lenny/main libgcc1 1:4.3.2-1.1em1 [23.7kB]
Get:57 http://www.emdebian.org/grip/ lenny/main libc6 2.7-18lenny4em1 [4,410kB]
Get:58 http://www.emdebian.org/grip/ lenny/main base-passwd 3.5.20em1 [11.5kB]
Get:59 http://www.emdebian.org/grip/ lenny/main base-files 5lenny7em1 [49.2kB]
Get:60 http://www.emdebian.org/grip/ lenny/main bash 3.2-4em1 [364kB]
Get:61 http://www.emdebian.org/grip/ lenny/main diff 2.8.1-12em1 [59.6kB]
Get:62 http://www.emdebian.org/grip/ lenny/main libcomerr2 1.41.3-1em1 [6,366B]
Get:63 http://www.emdebian.org/grip/ lenny/main e2fslibs 1.41.3-1em1 [91.3kB]
Get:64 http://www.emdebian.org/grip/ lenny/main libuuid1 1.41.3-1em1 [10.8kB]
Get:65 http://www.emdebian.org/grip/ lenny/main libblkid1 1.41.3-1em1 [21.6kB]
Get:66 http://www.emdebian.org/grip/ lenny/main libss2 1.41.3-1em1 [10.9kB]
Get:67 http://www.emdebian.org/grip/ lenny/main e2fsprogs 1.41.3-1em1 [234kB]
Get:68 http://www.emdebian.org/grip/ lenny/main findutils 4.4.0-2em1 [160kB]
Get:69 http://www.emdebian.org/grip/ lenny/main grep 2.5.3~dfsg-6em1 [128kB]
Get:70 http://www.emdebian.org/grip/ lenny/main gzip 1.3.12-6+lenny1em1 [44.0kB]
Get:71 http://www.emdebian.org/grip/ lenny/main login 1:4.1.1-6+lenny1em1 [50.6kB]
Get:72 http://www.emdebian.org/grip/ lenny/main mktemp 1.5-9em1 [5,772B]
Get:73 http://www.emdebian.org/grip/ lenny/main mount 2.13.1.1-1em1 [69.3kB]
Get:74 http://www.emdebian.org/grip/ lenny/main libsepol1 2.0.30-2em1 [96.4kB]
Get:75 http://www.emdebian.org/grip/ lenny/main sysvinit-utils 2.86.ds1-61em1 [17.8kB]
Get:76 http://www.emdebian.org/grip/ lenny/main initscripts 2.86.ds1-61em1 [33.6kB]
Get:77 http://www.emdebian.org/grip/ lenny/main sysv-rc 2.86.ds1-61em1 [13.7kB]
Get:78 http://www.emdebian.org/grip/ lenny/main sysvinit 2.86.ds1-61em1 [46.8kB]
Get:79 http://www.emdebian.org/grip/ lenny/main tar 1.20-1+lenny1em1 [148kB]
Get:80 http://www.emdebian.org/grip/ lenny/main tzdata 2010j-0lenny1em1 [749kB]
Get:81 http://www.emdebian.org/grip/ lenny/main util-linux 2.13.1.1-1em1 [293kB]
Get:82 http://www.emdebian.org/grip/ lenny/main balloon3-config 0.6 [2,400B]
Get:83 http://www.emdebian.org/grip/ lenny/main bsdutils 1:2.13.1.1-1em1 [17.0kB]
Get:84 http://www.emdebian.org/grip/ lenny/main libdevmapper1.02.1 2:1.02.27-4em1 [44.1kB]
Get:85 http://www.emdebian.org/grip/ lenny/main makedev 2.3.1-88em1 [15.8kB]
Get:86 http://www.emdebian.org/grip/ lenny/main ncurses-base 5.7+20081213-1em1 [16.4kB]
Get:87 http://www.emdebian.org/grip/ lenny/main procps 1:3.2.7-11em1 [160kB]
Fetched 15.4MB in 3s (4,819kB/s)
Download complete and in download only mode
I: Calculating obsolete packages
I: Extracting apt_0.7.20.2+lenny2em1_armel.deb...
 -> Processing conffiles for apt
I: Extracting balloon3-config_0.6_all.deb...
I: Extracting base-files_5lenny7em1_armel.deb...
 -> Processing conffiles for base-files
I: Extracting base-passwd_3.5.20em1_armel.deb...
I: Extracting bash_3.2-4em1_armel.deb...
 -> Processing conffiles for bash
I: Extracting bsdutils_1%3a2.13.1.1-1em1_armel.deb...
I: Extracting coreutils_6.10-6em1_armel.deb...
I: Extracting debconf-i18n_1.5.24em1_all.deb...
I: Extracting debconf_1.5.24em1_all.deb...
 -> Processing conffiles for debconf
I: Extracting debian-archive-keyring_2010.08.28~lenny1em1_all.deb...
I: Extracting debianutils_2.30em1_armel.deb...
I: Extracting dhcp3-client_3.1.1-6+lenny4em1_armel.deb...
 -> Processing conffiles for dhcp3-client
I: Extracting dhcp3-common_3.1.1-6+lenny4em1_armel.deb...
I: Extracting diff_2.8.1-12em1_armel.deb...
I: Extracting dpkg_1.14.29em1_armel.deb...
 -> Processing conffiles for dpkg
I: Extracting e2fslibs_1.41.3-1em1_armel.deb...
I: Extracting e2fsprogs_1.41.3-1em1_armel.deb...
 -> Processing conffiles for e2fsprogs
I: Extracting findutils_4.4.0-2em1_armel.deb...
I: Extracting gcc-4.3-base_4.3.2-1.1em1_armel.deb...
I: Extracting gnupg_1.4.9-3+lenny1em1_armel.deb...
I: Extracting gpgv_1.4.9-3+lenny1em1_armel.deb...
I: Extracting grep_2.5.3~dfsg-6em1_armel.deb...
I: Extracting grip-config_0.1.2em1_all.deb...
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W: GPG error: http://www.emdebian.org lenny Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B5B7720097BB3B58

Multistrap system installed successfully in /home/mike/celf/multistrap/RFS/.

Let’s explain the parameters:

  • armel is the architecture, for our example: arm in little endian
  • -d $PWD/RFS is the output directory containing the root filesystem. Be careful to pass an absolute path.
  • -f multistrap.conf is the name of the configuration file

If you look at RFS/dev, you will see that there are no device files in it. This will be a problem at boot time, unless you build a kernel with the below options:

CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y

Thanks to these parameters, the kernel will automatically mount a tmpfs filesystem on /dev, and will populate it with devices present on the system.

Now we have a root filesystem, but we still need to run the package configuration scripts to make it usable. The packages were installed, but their configuration scripts couldn’t be executed, because they can only run on the target architecture.

The easiest way to do this is to use NFS. On the host side, you need to export the root filesystem directory through NFS. On the target side you have to select /bin/sh for the init process. A typical kernel command could be:

console=ttyS0,115200 root=/dev/nfs nfsroot=192.168.0.1:/path/RFS rw ip=192.168.0.20 init=/bin/sh

Then boot your board. You should reach a command line.

First mount /proc:

mount -t proc nodev /proc

Then configure your packages using this command line:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin  dpkg --configure -a 

You will get a few questions about localization for tzdata, then the packages will be configured.

Finally go back to your host to change the RFS/etc/inittab file by uncommenting the below line and modifying it according to your serial console configuration (usually 115200). For example, replace

#T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100

by

T0:23:respawn:/sbin/getty -L ttyS0 115200 vt100

As we built this root filesystem as a normal user we may have problems with some setuid programs, which need to be owned by the root user. So let’s change the ownership of some directories:

sudo chown root:root -R RFS/bin RFS/usr/bin RFS/sbin RFS/usr/sbin

The last trick is to delete the root password by modifying RFS/etc/passwd, by replacing

root:x:0:0:root:/root:/bin/bash

by

root::0:0:root:/root:/bin/bash

You can now reboot your system without the init=/bin/sh kernel parameter. We now have a ready to use embedded Linux root filesystem with the power of Debian.

Other things to fix and do:

  • Configure the /etc/resolv.conf file to be able to connect to the Internet.
  • Configure the gateway in the ip= kernel parameter (ip=client-ip:server-ip:gw-ip:netmask:hostname:device:autoconf). For example:
    bootargs=console=ttyS0,115200n8 root=/dev/nfs ip=192.168.2.100::192.168.2.1:255.255.255.0:emdebian:eth0:off nfsroot=192.168.2.1:/home/mike/work/celf/
  • Install other packages such as mtd-utils and vim
  • Install kernel modules (either manually or through a kernel package)
  • Add a new user
  • Create a minimum /etc/fstab file

You now have a Debian system for which it is very easy to add new software, and which can be configured in a very familiar way. That’s great to make product prototypes, small, low-power and secure servers for home or office use, and in some cases, even real products.

Snowball, a new community Linux development platform

Snowball platformThe success of the BeagleBoard platform, a low-cost development platform, that has greatly contributed to the success of Texas Instruments OMAP3 processor in the embedded Linux industry, seems to have inspired another processor manufacturer: ST Ericsson. They have recently unveiled Snowball, a low-cost development platform for their AP9500 processor, which features a dual Cortex A-9 ARM core and a Mali 400 GPU.

The development board is designed and produced by our partner Calao Systems, and offers the following features:

  • The AP9500 processor, dual Cortex-A9 and Mali 400 GPU
  • 4 to 8 GB of e-MMC storage
  • 1 GB of LP-DDR2 RAM
  • Micro-SD slot
  • Ethernet connector, Wifi and Bluetooth
  • HDMI output, composite video output
  • Audio in/out
  • USB On The Go
  • Battery charger
  • On-board battery to keep time
  • Serial port connector, JTAG connector, MiPi 34 debug connector
  • Builtin GPS
  • 3-axis accelerometer, magnetometer and gyrometer, one pressure sensor
  • Expansion connectors to access SPI, I2C, LCD, MiPi devices, GPIO, UART, etc.
  • Last but not least, the board can be powered via USB (through a regular cable or through a Y one if power hungry devices like Wifi are used.)

The technical documentation page has a few more details, but at this time, they isn’t a lot of public information available about the AP9500 processor. I hope that ST Ericsson will fully understand how open source works and will soon release datasheets for the AP9500 in an open way. Interestingly, the AP9500 does not use the traditional PowerVR SGX 3D graphics core designed by Imagination Technologies and found in many other ARM processors, but instead uses the Mali graphics core, which is designed directly by ARM. It seems ARM has already open-sourced the kernel side bits of their graphic drivers, but it looks like a proprietary binary blob in userspace is still present.

The board will be available in two variants:

  • A Product Development Kit variant for 241 Euros.
  • A Software Development Kit variant for 165 Euros. My understanding is that the only difference between the two are the expansion connectors, present on the PDK variant but not on the SDK variant.

The board should be widely available at the end of Q2 2011, i.e around June, though at Bootlin, we will receive our first samples by the end of March thanks to our partnership with Calao Systems. The Snowball platform is supported by the Igloo Community, which hosts mailing-lists, an IRC channel, documentation and will also provide Meego and Android builds for the Snowball in the future.

Stay tuned on this blog. As soon as we get our own boards, we will write about our experiments with them.

CALAO boards supported in mainline U-Boot

CALAO SystemsI’m happy to announce that a couple days ago, support for the CALAO SBC35-A9G20, TNY-A9260 and TNY-A9G20 boards made its way into the U-Boot git repository. Sadly, it’s not possible to boot from an MMC/SD card with the SBC35 yet, but it’s something I’m currently working on.

Support for all these cards will be available in the next U-Boot release, due in November.