Magnus Hjorth wrote:

Those messages come from the Linux bootloader/decompression code, you 
can see the calls in arch/ppc/boot/simple/misc-embedded.c

Excellent, thank you.  It is all beginning to make sense now.  I see 
that this code also gives the ability to edit the command line over the 
serial link, something which was sucking up a whole 5 seconds of my boot 
time.  I might have a play with that :)

Thanks again, all the responses have been really useful.
-- Peter