Porting to RTOS

Hello,

I was wondering how easy or otherwise it would be to port PostgreSQL
to a real time operating system such as VxWorks?

What features of UNIX does PostgreSQL require? VxWorks is unlike UNIX
in that it runs like one single process containing many threads, so
fork() is out, but new threads can be created instead.

I don't believe I can add a postgres user -- is this required and, if
so, what for?

TCP/IP is supported under VxWorks.

Also, I'd like to get an idea of how suitable PostgreSQL is for
porting to an RTOS anyway. How big is it and can it be cut down to a
relatively small footprint? What sort of memory overhead does it
have? Has it been ported to any other RTOS?

Thanks in advance for any information, even if it is anecdotal!

Tim.