Re: gnat for DOS

[dewar@cs.nyu.edu (Robert Dewar)]

Scott James said:

"While your comment is perhaps relevant to GUI and OS-application
programming, with regards to embedded programming your repeated smirks at DOS
smack of either gross ignorance or wishful thinking.  Due to DOS's relatively
low system overhead, straightforward access to hardware, and the
proliferation of ROM DOS chips, rest assured DOS is and will remain with us
as a low-end embedded OS option for many years to come.  To continually bash
DOS does nothing for Ada and perhaps, in the future, should be relegated to
comp.os.advocacy or alt.windows.and.mice.are.really.cool or some
other such group."

You miss my point, I am not talking about DOS as a target environment. It
is quite true that since DOS is essentially completely transparent at run
time that if what you really want to do is to run on the bare board without
any OS intervention, DOS is perfectly reasonable.

My comment applies to DOS as a *development* environment, where it is indeed
lacking, since running on a DOS extender under DOS is always problematic
compared to using a proper 32-bit operating system.

Note that GNAT in any case does not run under DOS directly, nor do programs
that it generates. Instead they run in protected mode on a 32-bit DOS
extender. Your comments about embedded programming thus don't apply
directly, since in any case you do NOT have straightforward access to
the hardware, and here is no question of running in the context of
ROM DOS chips. 

It remains good advice for people doing serious development using GNAT
on a PC to choose one of the many 32-bit operating systems that is
supported. It is certainly true that DJGPP 2.0 alleviates some of the
worst characterstics of the DOS environment (notably the exhuastion of
low memory that made the use of gnatmake impossible), but still there
are limitations.

So my recommendations here have nothing whatever to do with operating
system advocacy, and are quite relevant to this group. Although it is
certainly possible to run GNAT under DOS, and even to build large
programs in this environment, you are buying yourself trouble. THis
is more a comment on GNAT and its system requirements than on DOS
per se. FOr example, the 8+3 character limits on file names are merely
a minor nuisance for most uses of DOS, but for writing large programs
using GNAT, this file naming restriction can be very bothersome.

That being said, we are continuing to enhance the DOS version. The next
release incorporates tasking, and also uses DJGPP 2.0 (so gnatmake should
finally be available).