Date   : Tue, 13 May 2003 15:50:49 +0100
From   : Richard_Talbot-Watkins@...
Subject: Re: Compiling Beebem

Steve Fewell wrote:

> The problem (in brief) is that the statement '?&FE6E=&A0' causes
> the emulated BBC to hang, when it should be initialising a 6522
> Interrupt (I think).

OK, I've investigated this a little further in BeebEm 1.41, and, yes, the
above line causes the
emulator to hang.  However, if I enter the following straight after a
reset:

P%=&900:[OPT2:LDA&FE6D:AND#&20:BEQP%+5:STA&FE6D:JMP!&206:]
?&206=0:?&207=9

...to provide a Timer 1 IRQ handler for the User VIA...

and then enter ?&FE6E=&A0, all is well.

I suspect a real Beeb may well do this too.  It's possible that what's
happening is the User VIA Timer 1 IRQ is being repeatedly generated, as
it's not being serviced (and the IRQ state cleared, as per the tiny IRQ2V
handler code above), thus causing the Beeb to hang.

Rich
--
                                                                           
 Rich Talbot-Watkins                       Richard_Talbot-Watkins@...      
 Sony Computer Entertainment Europe              Direct line: 01223 341865 
 Cambridge Studio                                                          
                                                                           






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