I've been trying to get the ppc 405 support under qemu to work for a bit for both "ppc405ref" board or "taihu" board emulation. Though I have had no success in getting it working.
Trying them with the u-boot firmware provided on the AMCC website for the "taihu" board, it dies somewhere just after u-boot initializes the SDRAM controller. I am also unable to get any type of serial output out to the serial console. Has this code ever fully booted and worked? If so how did you get it booting and working? On a side note. I've been hacking with some help to try and skip firmware with the latest Linux 4xx patches by Josh Boyer. These patches have a device tree in them so which allows for a way to by pass the need for firmware. But getting this to work has been challenge. The farthest I have gotten with this technique is getting qemu to load Linux and boot it (not fully of course...dies in early boot). But now it's a matter of getting open firmware entries into the kernel that are not provided by the device tree (they are expected to be passed). It's been a pain since can't get any serial output and having to look at buffers in gdb for output.