replace a legacy proprietary RTOS (Real-Time executive) with NetBSD!

Hi All,

We are evaluating to replace a legacy proprietary RTOS (Real-Time executive)
with NetBSD as one of the potential and leading candidates.
We would like to emulate legacy RTOS API on NetBSD. Part of the RTOS
application/client be ported to user-side and part of it may be ported to
kernel-side.
In this case we need to have two emulation layers one for kernel side and
another for user-side as the kernel side programming API is different from
user-side programming API.

I have few questions in this regard:

- Were there any such kind of migrations from a legacy RTOS to NetBSD
previously? If so what are the migration experiences, lessons learnt etc.

- Although man pages are good, it is difficult to figure out the what kind
of APIs it provides for a particular OS service for ex: synchronization and
communication services, threading services on both the kernel and user side.
Is there an architecture handbook that be quickly browsed to find out such
info and later refer to the man pages for more info?

- any other hints/suggestions about such a migration to NetBSD would be
helpful

Thanks in advance
Thiru