As of Mer 0.17testing10 we have an image that is fairly easy to try out on Nokia N900. This guide is for advanced users and there is NO WARRANTY. It might turn your N900 back into the crazy guy from this video or chew out your microSD, so be careful.

You will need:
* A microSD
* A SD/microSD card reader for your PC
* A Linux installation on your PC.
* A copy of a Mer rootfs for N900 (0.17testing10)
* A copy of the files in your /lib/firmware from your N900. This includes WiFi and Bluetooth firmware.
* PR1.0, PR1.0.1 or PR1.1 on your N900
* That you have installed fanoush's bootmenu (dpkg -i it and run 'Install bootmenu' application icon)

Instructions (must all be done as root):
* Partition your microSD to first partition being Linux and format it as ext3 using mkfs.ext3.
* Mount the ext3 partition on your PC, let's say in /mnt/mer.
* Make sure using 'mount' that your ext3 partition is -not- mounted 'nosuid' or 'nodev'
* cd /mnt/mer
* tar --numeric-owner -pzxf /full/path/to/mer-armel-n900-rootfs-v0.17testing10.tar.gz
* cd lib/firmware
* cp in the files from /lib/firmware from your N900
* umount /mnt/mer
* Make a file "mer.item" in /etc/bootmenu.d on your N900, containing:

ITEM_NAME="Mer (external SD, partition 1)"
ITEM_ID="mer"
ITEM_DEVICE="${EXT_CARD}p1"
ITEM_MODULES="mbcache jbd ext3"
ITEM_FSTYPE="ext3"
ITEM_FSOPTIONS="noatime,ro"

* Reboot your device, have the keyboard slid out. A bootmenu will appear where you can select Mer with the cursor keys.
* Mer booting.. wait for touchscreen calibration step
* And then you can run through the first boot wizard
* And a non-accelerated Mer desktop appears.

What works:
* WiFi
* Touchscreen
* Charging
* Watchdog handling

Of closed source blobs used in Mer (for N900):
* DSME (open source) with libcal (closed source) running from the Maemo5.0 rootfs
* BME running from the Maemo5.0 rootfs
* Firmware files for WiFi and Bluetooth chip amongst others.

Either way, I hope you enjoy playing with an alternative OS on your N900. Feel free to report bugs at http://wiki.maemo.org/Mer/Releases/0.17 and talk to us on #mer on irc.freenode.net if you'd like to contribute to Mer.

To shut down Mer, either sudo reboot or pop the battery.

For the N8x0 the way to create flashable rootfs's - that is, rootfs's usable in flasher-3.5 -r rootfs.jffs2 -f -R was through these two steps:

mkfs.jffs2 -d $ROOTFS_DIRECTORY -l -n -e 128KiB
-o rootfs.jffs2.raw
sumtool -l -n -e 128KiB -o rootfs.jffs2 -i rootfs.jffs2.raw

Now that the N900 uses ubifs for rootfs instead, how do you do create a flashable rootfs?

You need to make a file, ubinize.cfg:

[ubifs]
mode="ubi"
image="/full/path/to/base.ubi.img"
vol_id="0"
vol_size="200MiB"
vol_type="dynamic"
vol_name="rootfs"
vol_alignment="1"
vol_flags="autoresize"

Then, you run these two commands - you have to grab mtd-utils - Ubuntu Karmic has mtd-utils with ubifs support.

mkfs.ubifs -m 2048 -e 129024 -c 2047 -R 4MiB -r $ROOTFS_DIRECTORY -v /full/path/to/base.ubi.img
ubinize -o /full/path/to/ubi.img ubinize.cfg -m 2048 -p 128KiB -s 512

You can now run flasher-3.5 -r ubi.img -f -R.

What can this information be used for?

* Generate a full snapshot of your NAND rootfs and restore it with flasher after trying out something stupid that failed.

* Flash alternative OS'es onto your N900 NAND.

* Possibilities in rescue menu as in my previous post about bootmenu.sh hook - dump my rootfs to SD and I'll fix it on my PC and reflash it back to my N900.

This is slightly technical, but PR1.1 included a small but interesting patch to /sbin/preinit (part of getbootstate). /sbin/preinit is the first thing that gets run on Maemo5 for N900. Some history first: In the past we've always had to patch initfs or /sbin/preinit in order to get any sort of bootmenu on 770/N8x0(W)/N900. This has changed with PR1.1 - the patches are now part of Maemo5.0!

Besides some patches to aid MMC booting, what is added is few very important lines:

SLIDE_STATE=`cat /sys/devices/platform/gpio-switch/state`
if [ x"$SLIDE_STATE = "xopen" ]; then
echo_g "slide open, attempting to use bootmenu"
[ -f /bootmenu.sh ] && . /bootmenu.sh
fi

What does this mean? This means, that when you have the keyboard slid out at power on, it will look for /bootmenu.sh and try to include it in the boot process. If it doesn't exist, it goes on with business as usual.

This means, you can add have fanoush's bootmenu or your own rescue menu, or whatever could be interesting to have this early in the process.

Thanks to fanoush for his bootmenu and to Peter De Schrijver from Nokia for applying my patches.

Recently, three source packages that were published in Diablo times was released in their Fremantle versions which I had waited for a long time for. These are:

Just spent a day getting RTC (clock), battery charging and watchdogs working for Mer on N900 and I thought I'd like to share how it was done for those of you wanting to run other OS'es on N900. The watchdog package in typical Debian does not by default work with two watchdogs, so we are using DSME.

This example assumes that you have made a /mnt/initfs directory on your rootfs and that you're running this from fanoush's bootmenu which will put the Maemo5 root file system in /mnt/initfs

You should as early in your boot process (after udev has been started), run the following script:


# Set up initfs environment


hwclock --hctosys

chroot /mnt/initfs mount -n -t proc proc /proc

chroot /mnt/initfs mount -n -t sysfs sysfs /sys

mount --bind /dev /mnt/initfs/dev

chroot /mnt/initfs mount -n -t tmpfs -o size=1M,noatime tmpfs /tmp

chroot /mnt/initfs mount -n -t tmpfs -o size=256k,mode=0755,nosuid,noatime tmpfs /var/run

# Check current boot state. Could be 'USER'
export BOOTSTATE=`chroot /mnt/initfs getbootstate 2>/dev/null`

touch /mnt/initfs/tmp/$BOOTSTATE

echo $BOOTSTATE > /mnt/initfs/tmp/STATE

chroot /mnt/initfs /sbin/dsme -p /usr/lib/dsme/libstartup.so &

until chroot /mnt/initfs waitfordsme; do

sleep 1

done

LOGGER='/usr/bin/logger -s -tBME'

SYSFS_VBUS_PATH=/sys/class/i2c-adapter/i2c-1/1-0048/twl4030_usb/vbus


# check dead battery pre-charge

if [ $(cat $SYSFS_VBUS_PATH) -eq 1 ]; then

chroot /mnt/initfs /usr/sbin/bme_RX-51 -b

case $? in

0)

$LOGGER -pdaemon.notice 'precharge -> ok'

;;

2)

$LOGGER -pdaemon.crit 'precharge -> power off'

exit 1

;;

*)

$LOGGER -pdaemon.crit 'precharge -> failure'

;;

esac

fi

# Start battery management entity
chroot /mnt/initfs /usr/sbin/bme_RX-51 &

# Bonus: To get hald-addon-bme working (bad bad voodoo). We need to test if toggles_w's hald-addon-bme replacement works on N900.
# dpkg-repack hald-addon-bme from rootfs and dpkg -i it
mount --bind / /mnt/initfs/mnt/new_root
chroot /mnt/initfs ln -s /mnt/new_root/tmp/bme-dbus-socket /tmp/bme-dbus-socket
ln -s /mnt/initfs/tmp/.bmesrv /tmp/.bmesrv
ln -s /mnt/initfs/tmp/dsmesock /tmp/dsmesock

Starting from today, I will be officially starting my work as maemo.org distmaster. Nokia has gracefully sponsored this position for the community at the request of the maemo.org community council.

So, Maemo Summit 2009 is coming up - and many people who are contributing to Mer are going to this event.

This post is part two of my DebConf thoughts series, first post here. At DebConf we also attended three talks directly related to something we use quite often in Maemo and Mer: cross-compilation. The first was by Riku Voipio/suihkulokki about Scratchbox 2 (mirrored by me as I can't find the original URL) - which was also a maemo.org talk like ours, as well as the round-table session on Multiarch and a talk by Wookey on Crossbuilding on Debian for a derived distro.