Re: Ada Microkernel?

[Ted Dennison<dennison@telepath.com>]

In article <YSzU6.96$6d5.30076@news2-win.server.ntlworld.com>, Chris Campbell
says...
>
>it much.  I also object to people getting lazy and using classes that have kinda
>what they need but not quite and adding functionality to the class that's
>completely inappropriate.  Like reusing a soldier class for kangaroos! -- don't
>know if that story was true but it was funny!

The funny part was true. The "OO" part was not. It was just a simple mapping
(most likely done entirely in C or Fortran). The long story is: There are 3
basic kinds of simulators. There's the "Virtual" which is stereotypically a box
sitting on a 6-dof platform with a really expensive visual system and an exact
reproduction of the cockpit. There's the "Live", which I believe is typically
some kind of electronics hooked up to a real-live tank, jet, or rifle. Finally
there's the "Constructive", which is like a kind of wargame run entirely on
(usually) a single desktop-type computer, with the computer generating and
controlling most of the forces itself. 

It is quite typical for owners of virtual sims to want to hook them up to an
existing constructive sim that they already own, so that they can have loads of
computer-generated models running around on their pretty visuals for their
pilots to fly over, fight against, fight with, etc. Its also quite common for
their lists of entities to not quite match up between the two systems. The easy
solution for this problem is to just modify the virtual sim's mapping of the
constructive sim's entities. For example, when the constructive sim says that
the USS Arliegh Burke is steaming around, the virtual sim might instead display
the USS Grace Hopper. Obviously the more alike the two objects are, the better
this will work. :-)

There was one incident on a sim I worked on where a bug caused a heliocoper to
be displayed as a square-ish pile of rubble. To debug it, we had the maintinance
techs fly the two heliocopters in close formation for half an hour while we
monitored the DIS PDU traffic. The techs amused themselves during this time by
pretending it was a borg cube (in this case, with a heavy chicano acccent).
You'd be suprised how tough it is to adequately debug things while you're
laughing.

>That brings up an interenting point about Ada compilers and OO, specifically
>GNAT which is what most use i think.  I see very little in the Ada 95 language
>design that would need tied to an OS, but how much is there in practise?  There
>is no point saying use OO in the kernel if the compiler uses some system
>specifics to achieve it.  The only solution would be to modify GNAT which would

We've succesfully ported our entire (heavily-OO) flight trainer codebase from
vxWorks (GreenHills) to NT (Gnat). The only code that had to change was
system-specific stuff like setting the real-time clock frequency. I think at the
time that amounted to stubbing out 3 calls, and invoking the compiler. :-)

Of course NT isn't real-time, so its not very usable there. But it worked great
for occasional offline testing.

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