Editing SmartBox OS (section)

== Call types ==

There are three different types of machine code routines which can
be added to the controller.  Each one is suited to a more advanced level
than the other, which also relates to the amount of work needed to actually
get the routine working !  The three levels are such:

=== Simple stand alone routine ===

Here the routine is just the routine
itself with no supporting code (ie.  code to integrate with the rest of the
OS).  It has to be called directly, by use of the ExecuteCode JobCall, thus
it usually resides at a fixed address and obviously does not offer the user
friendly way of accessing itself like there is with normal OS calls.

=== Extended JobCall  ===

There is one JobCall in the OS (ExtendJob)
which can call various routines residing in memory, each one is identified
by a 8 bit number.  The disadvantages of this way is that the call hasn't
got it's own JobName/JobCode and needs the extra byte to identify itself. 
This is ideal for the quick routine which the user would like to add for
himself without having to resort to the extra code needed for the full
JobCode implementation.

=== Full JobCall ===

This is where the routine can define itself one
(or a number) of JobNames/JobCodes, it can integrate itself into an
extension of the OS in a complete way.  The disadvantage is that extra
coding is needed to deal with the various OS calls it has to service and
that extra work is needed to produce a suitable file to place in the
controller.

Normally with most processors, including the 65c02, the machine code
produced is produced for a fixed memory address, and it cannot be made to
run in a different place in memory unless extra work is carried out by the
user, or at least a combination of the user and the OS.  For the controller
this is a very severe disadvantage as most extensions are downloaded as
"modules" and to optimise memory a system has to be devised to enable
routines to be placed anywhere in memory, thus allowing no memory to be
wasted.  In the OS there is a routine to do just this, though it does need
some help.  A special version of the users code has to be developed, or
rather it has to be "processed" to add extra information on the end.  Extra
code is needed to set up a few pointers and call the OS routine to relocate. 
See later.