AVR-Chat

Hi Paul,

This untried, but pretty sure that I would go for:

//assume that we have 16 blocks of 256 in the array...
LDS r16,step  //this one 0-255?
LDS r17,num   //this one 0-15?
CLR r18	
LDI r30,LOW(array)
LDI r31,HIGH(array)
ADD r30,r16
ADC r31,r17
LPM r18,r30
OUT PORTD,r18

/*...and can be two cycles quicker if you dedicate a
   permanent pointer to 'step' and 'num' sequentially in SRAM:
	LD  r16,X
	LDD r17,X+1
  */


John S

Paul Maddox wrote:
> Dear all,
> 
>  I've long been a user of C on AVRs, but now I have need for speed, and I'm
> kinda stuck :-)
> I have a two dimensional array, called array[16, 256], stored in flash
> memory (these vaules won't change).
> and what I need to do is something like this ;-
> 
> PORTD = array[num, step] ; // C psuedo code
> 
> The array contains only 8 bit values,  but these are organised as 16 lots of
> 256 bytes.
> Any suggestions how, given that both 'num' and 'step' are variables held in
> ram.
> 
> Thanks in advance
> Paul
> 
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>