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About this blog

These are the ramblings of Matthijs Kooijman, concerning the software he hacks on, hobbies he has and occasionally his personal life.

Most content on this site is licensed under the WTFPL, version 2 (details).

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Replaced GPG key

For anyone that cares: I just replaced my GPG (Gnu Privacy Guard) key that I use for signing my emails and Debian uploads.

My previous key was already 9 years old and used a 1024-bit DSA key. That seemed like a good idea at the time, but for some time these small keys and signatures using SHA-1 have been considered weak and their use is discouraged. By the end of this year, Debian will be actively removing the weak keys from their keyring, so about time I got a stronger key as well (not sure why I didn't act on this before, perhaps it got lost on a TODO list somewhere).

In any case, my new key has ID A1565658 and fingerprint E7D0 C6A7 5BEE 6D84 D638 F60A 3798 AF15 A156 5658. It can be downloaded from the keyservers, or from my own webserver (the latter includes my old key for transitioning).

Now, I should find some Debian Developers to meet in person and sign my key. Should have taken care of this before T-Dose last year...

 
0 comments -:- permalink -:- 14:03
Debian Squeeze on an emulated MIPS machine

In my work as a Debian Maintainer for the OpenTTD and related packages, I occasionally come across platform-specific problems. That is, compiling and running OpenTTD works fine on my own x86 and amd64 systems, but when I my packages to Debian, it turns out there is some problem that only occurs on more obscure platforms like MIPS, S390 or GNU Hurd.

This morning, I saw that my new grfcodec package is not working on a bunch of architectures (it seems all of the failing architectures are big endian). To find out what's wrong, I'll need to have a machine running one of those architectures so I can debug.

In the past, I've requested access to Debian's "porter" machines, which are intended for these kinds of things. But that's always a hassle, which requires other people's time to set up, so I'm using QEMU to set up a virtual machine running the MIPS architecture now.

What follows is essentially an update for this excellent tutorial about running Debian Etch on QEMU/MIPS(EL) by Aurélien Jarno I found. It's probably best to read that tutorial as well, I'll only give the short version, updated for Squeeze. I've also looked at this tutorial on running Squeeze on QEMU/PowerPC by Uwe Hermann.

Finally, note that Aurélien also has pre-built images available for download, for a whole bunch of platforms, including Squeeze on MIPS. I only noticed this after writing this tutorial, might have saved me a bunch of work ;-p

Preparations

You'll need qemu. The version in Debian Squeeze is sufficient, so just install the qemu package:

$ aptitude install qemu

You'll need a virtual disk to install Debian Squeeze on:

$ qemu-img create -f qcow2 debian_mips.qcow2 2G

You'll need a debian-installer kernel and initrd to boot from:

$ wget http://ftp.de.debian.org/debian/dists/squeeze/main/installer-mips/current/images/malta/netboot/initrd.gz
$ wget http://ftp.de.debian.org/debian/dists/squeeze/main/installer-mips/current/images/malta/netboot/vmlinux-2.6.32-5-4kc-malta

Note that in Aurélien's tutorial, he used a "qemu" flavoured installer. It seems this is not longer available in Squeeze, just a few others (malta, r4k-ip22, r5k-ip32, sb1-bcm91250a). I just picked the first one and apparently that one works on QEMU.

Also, note that Uwe's PowerPC tutorial suggests downloading a iso cd image and booting from that. I tried that, but QEMU has no BIOS available for MIPS, so this approach didn't work. Instead, you should tell QEMU about the kernel and initrd and let it load them directly.

Booting the installer

You just run QEMU, pointing it at the installer kernel and initrd and passing some extra kernel options to keep it in text mode:

$ qemu-system-mips -hda debian_mips.qcow2 -kernel vmlinux-2.6.32-5-4kc-malta -initrd initrd.gz -append "root=/dev/ram console=ttyS0" -nographic

Now, you get a Debian installer, which you should complete normally.

As Aurélien also noted, you can ignore the error about a missing boot loader, since QEMU will be directly loading the kernel anyway.

After installation is completed and the virtual system is rebooting, terminate QEMU:

$  killall qemu-system-mips

(I haven't found another way of terminating a -nographic QEMU...)

Booting the system

Booting the system is very similar to booting the installer, but we leave out the initrd and point the kernel to the real root filesystem instead.

Note that this boots using the installer kernel. If you later upgrade the kernel inside the system, you'll need to copy the kernel out from /boot in the virtual system into the host system and use that to boot. QEMU will not look inside the virtual disk for a kernel to boot automagically.

$ qemu-system-mips -hda debian_mips.qcow2 -kernel vmlinux-2.6.32-5-4kc-malta -append "root=/dev/sda1 console=ttyS0" -nographic

More features

Be sure to check Aurélien's tutorial for some more features, options and details.

 
0 comments -:- permalink -:- 12:18
Booting an old Sparc Ultra1 with dead NVRAM

Sun Ultra1

To be able to debug a bug in OpenTTD that only occured on SPARC machines, I needed an old SPARC machine so I could reproduce and hopefully fix the bug. After some inquiring at our local hackerspace, Bitlair (which had a few SPARC32 machines lying around, but I needed SPARC64), I got in touch with The_Niz from NURDSpace, the hackerspace in Wageningen. Surprisingly, it turned out I actually knew The_Niz already through work :-)

In any case, The_Niz was kind enough to lend me a SPARC Ultra1 workstation and Sun keyboard, and r3boot gave me a Sun monitor I could use (of course Sun hardware doesn't use a regular VGA connector...).

There was one caveat, though: The NVRAM battery in the Ultra1 was dead. The NVRAM chip stores the boot settings (like the BIOS settings in a regular PC), but also the serial number and MAC address of the machine (called the IDPROM info). Without those settings, you'll have to manually select the boot device on every boot (by typing commands at a prompt) and netbooting does not work, for lack of a MAC address (I presume regular networking, e.g., from within Linux, does not work either, but I haven't tested that yet).

Sun has taken an interesting approach to their NVRAM chip. Where most machines just use a piece of EEPROM (Flash) memory, which does not need power to remember its contents, Sun has used a piece of RAM memory (which needs power to remember its contents) combined with a small rechargeable battery.

This means that when the machine is not used for a long time or is very old, the battery will eventually die, causing the machine to spit out messages like "The IDPROM contents are invalid and "Internal loopback test -- Did not receive expected loopback packet".

I needed to install Debian on this Ultra1, so I needed some way to boot the installer. Since netbooting did not work, my first attempt was to ignore the NVRAM problem and just get the machine to boot off a Debian boot cd. This did not quite work out: the cdrom player in the Ultra1 (a 4x burner connected through SCSI) didn't like any of the CD-Rs and CD-RWs I threw at it. It spat out errors like "Illegal Instruction", "Program Terminated" or "SProgram Terminated" (where the first "S" is the start of "SILO", the SPARC bootloader).

As we all remember from a long time ago, the early generation CD-ROM players were quite picky with burnt CDs, so also this one. I found some advice online to burn my CDs at a lower speed (apparently the drive was rumoured to break on discs burned at 4x or higher), but my drive or CD-Rs didn't support writing slower than 8x... I could write my CD-RW at 4x and at one occasion I managed to boot the installer from a CD-RW and succesfully (but very, very slowly) scan the CD-RW contents, but then it broke with read errors when trying to actually load files from the CD-RW.

So, having no usable CD-ROM drive to boot from, I really had to get netboot going. Apparently it is possible (and even easy and not so expensive) to replace the NVRAM chip, but I didn't feel like waiting for one to be shipped. There is a FAQ available online with extensive documentation about the NVRAM chip and instructions on how to reprogram the IDPROM part with valid contents.

So, I reckoned that the battery was only needed when the machine was powered down, so I should be able to reprogram the IDPROM info and then just not poweroff the system, right?

Turns out that works perfectly. I reprogrammed the IDPROM using the MAC address I read off the sticker on the NVRAM chip and made up a dummy serial number. For some reason, the mkpl command did not work, I had to use the more verbose mkp command. Afterwards, I gave the reset command and the "Internal loopback test" error was gone and the machine started netbooting, using RARP and TFTP.

By now, I've managed to install Debian, get Xorg working and reproduce the bug in OpenTTD, so time for fixing it :-D

 
0 comments -:- permalink -:- 17:06
Thinkpad X201 mute button breaking speaker output

Thinkpad

Recently, I was having some problems with the internal speakers on my Lenovo Thinkpad X201. Three times now, the internal speakers just stopped producing sound. The headphone jack worked, it's just the speakers which were silent. Nothing helped: fiddling with volume controls, reloading alsa modules, rebooting my laptop, nothing fixed the sound...

When trying to see if the speakers weren't physically broken, I discovered that booting into Windows actually fixed the problem and restored the sound from the speakers. It's of course a bit of a defeat to accept Windows a fix for my problem, but I was busy with other things, so it sufficed for a while.

When migrating my laptop to my new Intel SSD, I broke my Windows installation, so when the problem occured again, I had no choice but to actualy investigate it.

I'll skip right to the conclusion here: I had broken my sound by pressing the mute button on my keyboard... Now, before you think I'm stupid, I had of course checked my volume controls and the device really was unmuted! But it turns out the mute button in Thinkpads combined with Linux is a bit weird...

This is how you would expect a mute button to be implemented: You press the mute button, it sends a keypress to the operating system, which then tells the audio driver to mute.

X201 volume buttons

This is how it works on my Thinkpad: You press the mute button, causing the EC (embedded controller) in the thinkpad to directly mute the speakers. This is not visible from the normal volume controls in the software, since it happens on a very low level (though the thinkpad_acpi kernel module can be used to expose this special mute state through a /proc interface and special audio device).

In addition to muting the speakers, it also sends a MUTE acpi keypress to the operating system. This keypress then causes the audio driver to mute the audio stream (actually, it's pulseaudio that does that).

Now, here's the fun part: If you now unmute the audio stream through the software volume controls, everything looks like it should work, but the hardware is still muted! It never occured to me to press the mute button again, since the volume wasn't muted (or at least didn't look like it).

I originally thought that the mute button handling was even more complex, when I found some register polling code that faked keypresses, but it seems that's only for older Thinkpads (phew!).

In any case, the bottom line is: If you have a Thinkpad whose speakers suddely stop working, try pressing the mute button!

 
0 comments -:- permalink -:- 00:13
Copyright by Matthijs Kooijman