automake and subdirectories

[Nicholas Kidd]

I was wondering what the proper was to set up Makefile.am files in a
directory layout like so:

proj/
   proj.c               <-- contains main
   machine_dep_dir/     <-- contains machine dependent code
                            will reference machine independent code
   machine_indep_dir/   <-- like it says, machine independent.


I have read the online docs and it seems that the right thing to do is
build a library.  But why not just build all the needed files
into one binary app?  In more general, how do you make subdirectories for
your project's code-layout that conform to logical boundaries ( but
logical section 1 may include that of section 2 and vice versa ) and
not spend the time building a library?
If it is not a waste to create libraries and then combine those with
the top level source file then that is fine.  I just thought there
might be some way to tell automake something like this:

"Every .cpp file in subdirs x,y,z should be compiled and linked into this
application"

Thanks,
-Nick Kidd