Re: Extended Exceptions and other tweaks.

[Brian Drummond <brian@shapes.demon.co.uk>]

On Mon, 08 Apr 2013 10:21:04 +0000, Brian Drummond wrote:

> On Sun, 07 Apr 2013 13:20:52 -0700, rrr.eee.27 wrote:
> 
>> On Saturday, April 6, 2013 5:49:55 PM UTC+2, Lucretia wrote:
>>> On Monday, 1 April 2013 21:36:58 UTC+1, Brian Drummond  wrote:

>> Also in the configurable run time mode you need the files
>> a-except.ad[sb].  They can be very short, however. Have look at these
>> files in the latest AVR-Ada (V1.2.1).  Local exceptions -- including
>> user defined ones -- are possible in AVR-Ada.
> 
> It would be interesting to know if porting these helps Luke's situation.
> 
> I have borrowed the AVR-Ada RTS as a starting point for the TI MSP430
> and it's looking good so far. I haven't tried exceptions yet though, but
> I'll report when I get that far.

Played with exceptions tonight; they look better than I expected and I 
think I can shed some light on Luke's experiments. 

(NOTE: all the following apply with "pragma No_Exception_Propagation" in 
effect)

The a-except.ad[sb] from AVR-Ada _nearly_ worked for the MSP430 as well! 
The address clause on "procedure Reset" was the only point of failure so 
far, as it is not 0 on the MSP430 but 16#FF80# or other CPU-dependent 
value.

What's untested so far:
Actually running the executables : so far I have just examined the code 
emitted by the compiler

Raising exceptions as a result of runtime errors (overflow etc) instead 
of explicit Raise statements.

What works :
Raising a standard exception.
Handling it locally
Handling it in the Last Chance Saloon (cough, Handler).

Raising a user-defined exception, declared immediately visible to the 
subprogram which raises and handles it.
Handling it locally.
Handling it in the Last Chance handler.

Raising a user-defined exception, declared elsewhere - even in a local 
package.
Handling it in the Last Chance handler.


What doesn't work :

Locally handling a user-defined exception from another package, via a 
selected name. The compiler ignores (deletes) any local handler and 
passes the exception (actually just plants a call to) the Last Chance 
handler. However, making the exception directly visible via a Use clause, 
it does work.

So the following , 

raise Timer_A.oops;	-- last chance handler!
and
use Timer_A;
raise oops;		-- can be locally handled

end up in different exception handlers!

I'm not clear on whether this is expected behaviour...

- Brian