OpenWRT on a Nokia N800

This is work in progress, so expect it to be added to/abandoned (probably the latter) at any time.

I’ve got a Nokia N800 whose screen is on its way out that I’d like to find some other use for. Since Nokia seems to have abandoned this device, it looks like I’m on my own.  (To think I used to like their products!)  Good thing I still have a copy of the firmware, and found a copy of the flasher software.  Let’s hope Nokia really doesn’t care, and lets this link stay here.

Anyway it looks like OpenWRT supported it once upon a time – it’s still listed in the source tree, albeit broken.  The omap24xx doesn’t seem to be in any of the branches or tags, so I don’t know how things get there.  Revision 30798 seems to be before they added the “broken” tag, so maybe that’s a good place to start.

$ git clone https://github.com/mirrors/openwrt.git
$ cd openwrt.git
$ git checkout 2f3210027ca1393766b0293b1bdd9fc6a13e88d7
$ git branch n800
$ git checkout n800

So now you apparently:

$ make defconfig
$ make menuconfig

select the N800/810 as the target

$ make

I had a problem with mklibs not working with GCC 4.7, which was easily fixed (I made it as a patch).

And that worked for me!  In bin, I have a kernel, root filesystem and so on.

Testing it out

I happened to notice that you can boot a kernel that’s been loaded into RAM:

$ sudo flasher-3.5 -k openwrt-omap24xx-zImage \
    -r openwrt-omap24xx-root.squashfs -l -b"root=/dev/ram0"

That seemed to work, and the kernel output appears on my dodgy screen.  That stuff with the root filesystem didn’t seem to work, but I noticed that the kernel was trying to look for the root filesystem on an MMC card.  I grabbed a convenient SD card and put the root filesystem on it, and the boot process seemed to go a bit further.

One problem: I get “Press enter to activate this console”.  Without a keyboard, how will I do that?

Adding a keyboard

Now that it boots, how am I going to communicate with it?  It’s alright for a N810, which has a keyboard, but the N800 doesn’t.  Apparently there’s a serial port in the back near the battery, but I don’t know how I’d attach cables to those pads.  Maybe I can plug a USB keyboard into the USB OTG port.

Maybe someone has sorted it out – Google to the rescue again!  Apparently you have to:

$ make menuconfig
Base system:
 <*> busybox:
   Linux System Utilities:
     <*> lsusb
 Kernel modules:
   USB Support:
     <M> kmod-usb-hid

The kernel module was already selected for me.  Exit, save, then make.

Looking in the new root filesystem, lsusb is there.

I just found out about 0xFFFF, another flasher for this device.  Let’s give it a whirl:

$ sudo 0xFFFF -i
...
Device's USB mode is 'client

Maybe the USB port needs to be switched into OTG mode.

$ sudo src/0xFFFF -U 1
...
Set USB mode to: 'host'.

I’ll try loading the kernel again, and… no luck

Maybe OpenWRT doesn’t have any hotplugging function.  I’ll try logging as much as possible on the console by setting klogconloglevel to 8 in /etc/config/system.  But there are two problems with this: I want to see syslog, not the kernel log; and that property doesn’t seem to be used anyway.

During random googling, I found a link to Qemu. It turns out Qemu can emulate the N800! There seemed to be no keyboard input – since the n800 doesn’t have a keyboard – but apparently the connector near the battery is the 3rd serial port. So you can solicit a terminal like this:

$ qemu-system-arm -machine n800 -drive file=root,if=sd -kernel \
  openwrt-omap24xx-zImage -serial vc -serial vc -serial stdio

where root is an SD card image containing the root filesystem.

Now I’ve got something I can interact with, which should make things easier! (It sounds like the Bluetooth module is connected to one of the UARTs, which the above command might upset.)

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