Lpc2000

After some research in other samples I found a tip :

I have to change a line in the default startup.s :


--------------------------------------------------------------------
  .section .vectors, "ax"
  .code 32
  .align 0

/*****************************************************************************
 * Exception Vectors                                                 
       *
 *****************************************************************************/
_vectors:
  ldr pc, [pc, #reset_handler_address - . - 8] /* reset */
  ldr pc, [pc, #undef_handler_address - . - 8] /* undefined instruction */
  ldr pc, [pc, #swi_handler_address - . - 8] /* swi handler */
  ldr pc, [pc, #pabort_handler_address - . - 8] /* abort prefetch */
  ldr pc, [pc, #dabort_handler_address - . - 8] /* abort data */
  .word 0xB9205F84 /* boot loader checksum */

  ldr pc, [pc, #irq_handler_address - . - 8] ----------->  TO LDR PC,
[PC, #-0xFF0]

  ldr pc, [pc, #fiq_handler_address - . - 8]

------------------------------------------------------------------

I don't understand the mean of this modificication but it works ? 
Why #-0xFF0 ? 
What's that syntax : _ . - 8 ?

thanks in advance !




--- In lpc2000@yahoogroups.com, "Randy Ott" <randy@t...> wrote:
> Yann,
> 
> Unless you supply an irq_handler, the default weak symbol will be 
> linked and the interrupt will branch to an infinite loop.  I use a 
> handler in C that looks like this:
> ==================================
> __irq __arm void irq_handler(void)
> {
>   void (*interrupt_function)();
>   unsigned int vector;
> 
>   vector = VICVectAddr;   // Get interrupt vector.
>   interrupt_function = (void(*)())vector;
>   (*interrupt_function)();  // Call vectored interrupt function.
> 
>   VICVectAddr = 0;        // Clear interrupt in VIC.
> }
> ==================================
> I don't know how the __irq and __arm attributes are declared in 
> Crossworks.  If it is GNU then I believe you need to change the 
> function declaration to:
> 
> irq_handler(void) __attribute__ ((interrupt ("IRQ")))
> 
> Hope this helps.
> 
> Randy Ott
> 
> 
> 
> --- In lpc2000@yahoogroups.com, "nourson54" <yannsuisini@h...> wrote:
> > Hi,
> > 
> > I'm trying to play with interrupts with Crossworks but I can't get 
> it
> > working , even with the samples code (timer0 interrupt) .
> > I debug with Olimex JTAG .
> > I put a breakpoint on my interrupt ISR but it never breaks on it 
> > but in the startup code :
> > 
> > "/*****************************************************
> >  
> *                                                                   
> >         *
> >  * Default exception 
> handlers                                        
> >         *
> >  * These are declared weak symbols so they can be redefined in user
> > code.     * 
> >  
> *                                                                   
> >         *
> >  *****************************************************/
> > 
> > undef_handler:
> >   b undef_handler
> >   
> > swi_handler:
> >   b swi_handler
> >   
> > pabort_handler:
> >   b pabort_handler
> >   
> > dabort_handler:
> >   b dabort_handler
> >   
> > irq_handler:
> >   b irq_handler      <-----------------------  BREAKS HERE 
> >   
> > fiq_handler:
> >   b fiq_handler
> > 
> >   .weak undef_handler, swi_handler, pabort_handler, dabort_handler,
> > irq_handler, fiq_handler
> > 
> > 
> > 
> > Could someone help me ? 
> > 
> > thx
> > 
> > Yann
> > 
> > 
> > PS: I'm a newbie in ARM world ;-) So excuse me if it seems a 
> trivial
> > question :-P