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Niklas Holsti <[log in to unmask]>
Thu, 8 Aug 2002 10:23:08 +0300
text/plain (56 lines)
On Wed, Aug 07, 2002 at 12:41:37PM +0100, Gloster wrote:
> Niklas Holsti mentioned:
> "[..] Software development started in Janauary 2002 and will
> use the XGC Ada compiler (a variant of Gnat) with the
> Ravenscar tasking profile. [..]"
> After reading XGC manuals and speaking to one of the XGC compiler
> writers, I still have not lost the impression that whatever software
> I could get from XGC, I could just get the same from the New York
> GNAT FTP download site. Is my impression correct?
> Regards,
> Colin Paul Gloster

As I understand it, XGC provide their own kernel (limited to
Ravenscar) and have tailored the Gnat front-end to interface
more directly with this kernel, without all the layers that
are present in the standard Gnat. They also support a number
of other profiles that are even less permissive, for more
critical systems. Their compiler also excludes certain other
Ada language features so that they can make do without the
"secondary stack".

We chose the XGC compiler and kernel for this project based on
a comparison of the real-time performance between various
Ada systems for the ERC32 processor. This comparison was made
by ESA/ESTEC some time ago, and included (if I remember correctly)
also Gnat/ORK, Gnat/RTEMS, and a system from Aonix. When the
comparison was made, the XGC and Aonix systems were considerably
faster in tasking than Gnat/ORK and Gnat/RTEMS. I have heard
that the latter two systems have been improved, so a new comparison
would be interesting, but I haven't seen numbers.

XGC sells a complete package tailored to the ERC32, including
start-up modules etc., with technical support. Our project
requirements originally included some tasking features (CPU
time and real-time monitoring) that would have required kernel
extensions, and we got the impression that XGC would have been
able and willing to make such extensions. These requirements have
later been reduced, so we can now make do with just the standard
Ada features (Ravenscar subset, of course).

I haven't investigated the NY FTP site recently -- are there
Ravenscar kernels for download?


Niklas Holsti

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