AVR-Chat

On Thu, 4 Aug 2005, Kevin Laborda wrote:

> First, I use AVR Assembly.  The thing that confuses me is when initiliazing the vector table how do I "skip" the vectors I don't want.  Isn't the order important when listing the interrupts. Example code:
> 
>  .ORG 0000 ; Address is zero
>     RJMP Start ; The reset-vector on Address 0000
>     RJMP IService ; 0001: first Int-Vector, INT0 service routine
> [...] here other vectors 
> 
> if I don't want the interrupt at the 000x location do I use reti? 
> From tn13def.inc:
> 
> ;**** Interrupt Vectors ****  
> .equ INT0addr      =$001 ;External Interrupt0
> .equ PCINT0addr    =$002 ;Pin Change Interrupt0
> .equ TIM0_OVF0addr      =$003 ;Overflow0 Interrupt 
> .equ EE_RDYaddr      =$004 ;EEPROM write complete
> .equ ANA_COMPaddr =$005 ;Analog Comparator Interrupt 
> .equ TIM0_COMPAaddr      =$006 ;Timer/Counter0 Compare Match A  
> .equ TIM0_COMPBaddr    =$007 ;Timer/Counter0 Compare Match B  
> .equ WDTaddr       =$008 ;Watchdog Timeout
> .equ    ADCaddr      =$009 ;ADC Conversion Complete Handle
> 
> So, after Reset ($000?), I'd have the INT0addr followed by PCINT0addr etc.  If I only want reset then the Overflow0 Interrupt would I do
> 
> .ORG 0000
>   RJMP Reset
>   RETI
>   RJMP Timer
>   RETI
>   RETI
>   RETI
>   RETI
>   RETI 
> 
> followed by initializing the stack and timer/prescaler in the Reset label code section?
> 

You can do it that way, but I assume if I am not planning on using a given 
interrupt, it doesn't matter what is in that vector location.  It hasn't 
gotten me into troble yet (fingers crossed!).  What I usually do is:

 .ORG 0000
   RJMP Reset
 .ORG 0003  
   RJMP Timer
 .ORG 0009
   RJMP ADCSVC

That way I only write code for the interrupts I'm using.


> Also would the following work for generic stack initialization (for what I need)?
> 
> .def TEMP = r16
> [...]
> Reset:
> ldi TEMP,low(RAMEND) ; Set stackptr to ram end
> out SPL,TEMP
> ldi  TEMP, high(RAMEND)
> out  SPH, TEMP
> [ Timer0 initialization]
> sei
> 
> or does the ATtiny13 require something else?
> 
> Thanks,
> 
> Kevin

Not sure about the ATtiny13 as I haven't used that one yet, but it should 
work with ATmega8, ATmega16, etc.

Zack