Thanks to a kind donator, I now own a Nokia dbox2 with IDE interface. (For those that don't know - the dbox2 is a settop box designed for german paytv 10 years ago in a way that its bootloader would only run signed software. A limitation that was put aside by some cool hackers early in this century. Nowadays it usually runs Linux on its 66MHz powerpc CPU, 32MB RAM and 8MB FLASH ROM. Later some cool guys designed an IDE interface that plugs into the memory expansion slot)
The main use of such an IDE interface for most people is to use the box as a video recorder. However, I am already doing this via the ethernet port, wich is more practical for me than a built in disk.
I would have deemed it much more useful if I was able to boot from the IDE drive, since that would make it much easier to try out new experimental code without needing to upgrade the FLASH image all the time (having the known working version in FLASH as a fallback is mandatory for good WAF).
So I pondered the problem and found out, that people had already implemented basic support for the IDE interface in U-Boot (which is used as a "second stage" bootloader), and it could already access and read the disk.
Unfortunately, U-Boot needs to be in FLASH, and this U-Boot would then only boot from disk.
So I have been hacking on making U-Boot actually read multiple boot command lines (and and option which one to boot as default) from a config file in the /var/ partition of the FLASH which makes it pretty easy to switch the device we boot from. It is now actually similar to the boot process of the Tripledragon.
The only thing that's missing now is a driver for the front panel keys, so that you can change the selection on the fly without using a serial console. That's coming next, after the summer vacation ;)