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???
09/07/09 22:47
Modified:
  09/07/09 22:48
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 		 #168786 - what to unroll
Responding to: ???'s previous message
Gonzalo unrolled the loop over P2 in the inner loop, thereby saving 28% time compared to P2 unrolled in the outer loop (which is a few bytes shorter).

Save This Code
	clr a
	mov r0, a
	mov p2, a
	cpl a
lp0:	movx @r0, a  ;P2 = 0
	djnz r0, lp0
	inc p2
lp1:	movx @r0, a  ;P2 = 1
	djnz r0, lp1
	inc p2
lp2:	movx @r0, a  ;P2 = 2
	djnz r0, lp2
	inc p2
lp3:	movx @r0, a  ;P2 = 3
	djnz r0, lp3
 
But if you use an auto-incrementing DPTR as you mentioned and keep counting in R0 and/or R1 using DJNZ you gain little from the auto-increment. (Checking DPL and/or DPH is even more expensive.)

Save This Code
	clr a
	mov r0, a
	mov r1, #4
	mov dptr, #0
	mov autoinc, #1 ;or whatever it takes
	cpl a
lp0:	movx @dptr, a
	djnz r0, lp0
	djnz r1, lp0    ;no unroll
 
Save This Code
	clr a
	mov r0, a
	mov dptr, #0
	mov autoinc, #1 ;or whatever it takes
	cpl a
lp0:	movx @dptr, a   ;DPH = 0
	djnz r0, lp0
lp1:	movx @dptr, a   ;DPH = 1
	djnz r0, lp1
lp2:	movx @dptr, a   ;DPH = 2
	djnz r0, lp2
lp3:	movx @dptr, a   ;DPH = 3
	djnz r0, lp3
 
Now with a different unroll you do start to gain.

Save This Code
	clr a
	mov r0, a
	mov dptr, #0
	mov autoinc, #1 ;or whatever it takes
	cpl a
lp0:	movx @dptr, a   ;DPL = 0xn0/4/8/C
	movx @dptr, a   ;DPL = 0xn1/5/9/D
	movx @dptr, a   ;DPL = 0xn2/6/A/E
	movx @dptr, a   ;DPL = 0xn3/7/B/F
	djnz r0, lp0
 
You can choose how far to unroll and adjust R0 accordingly.

List of 11 messages in thread
TopicAuthorDate
Fastest way to fill buffer            01/01/70 00:00      
   something like this            01/01/70 00:00      
   when software hits limits...            01/01/70 00:00      
      auto-increment            01/01/70 00:00      
         Two questions ..            01/01/70 00:00      
         But Gonzallo unrolled it already isn't it?            01/01/70 00:00      
            Yes, but not with the hardware increment            01/01/70 00:00      
                be specific            01/01/70 00:00      
                  Don't forget about the Maxim/Dallas parts!            01/01/70 00:00      
            what to unroll            01/01/70 00:00      
               Well, what you CAN do ...            01/01/70 00:00      

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