Re: Is it possible to build an Ada cross-compiler for an 8-bit embedded target now that gcc 3.X has support for Ada?

[Peter Amey <peter.amey@praxis-cs.co.uk>]

Peter Milliken wrote:
 > Subject pretty much says it all.
 >
 > Now that you can build an Ada compiler using gcc 3.X (well, according 
to the
 > build instructions of gcc 3.x :-)), I began to wonder whether it was
 > possible to build a cross-compiler for an 8-bit target processor. The 
8-bit
 > processor family in question is already supported by gcc (I believe).

Peter,

Given that there is already a C compiler for your target, one approach 
might be to _design_ in Ada and then use an Ada->C compiler/translator 
to convert the design to C for compilation.  In practice you can tie the 
translator and C compiler so tightly together that it looks like an Ada 
compiler.

The biggest problem with this approach in general is the size of the 
run-time library you need to support all of Ada (esp. tasking, exception 
handling etc.) and writing such a library for a small processor.  We 
have had some success in avoiding these problems by using SPARK as the 
design language.  This gives several benefits:

1. SPARK is designed to need zero (or at least very little) run-time 
library support so all the generated C is directly and easily traceable 
back to some SPARK source statement.

2.  Using the SPARK tools you can easily prove the code to be exception 
free (e.g. no range violations) and this means the translation can be 
greatly simplified because it does not have to include the run-time 
checks that a full Ada compiler would place in the code.  The SPARK 
tools can be told how big your C int is, for example, and can ensure 
there are no overflows in the translated code.

3.  You can do a great deal of strong verification on the SPARK "design 
model" before generating the C and therefore greatly reduce the cost of 
the testing process.

We have submitted a paper to Ada Europe 2004 on this topic.

regards

Peter

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Peter Amey                              Principal Consultant

Praxis Critical Systems
20, Manvers St.                         +44 (0)1225 466991
Bath                                    www.praxis-cs.co.uk
BA1 1PX                                 www.sparkada.com
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