Polling register - which is better?

[javor.pas]

Hi all.

I have a question: which is better when polling a register for example - polling a register to check if the Flash/EEPROM operation is complete


1.

Code: Select all

while NVMCON.15 = 1 do ;

or

2.

Code: Select all

while NVMCON.15 = 1 do
  nop;

I think this nop instruction is not needed but - let the specialists tell their opinion. The goal is to achieve fastest respond time with fewer instructions. Please share your opinion.

Regards,

Javor.pas

[SamY Fareast]

Hi javor.pas.
I am not a specialist. but I wrote this code and compiled.

Code: Select all

program ForumQuest;

begin
  {This couldnt be compiled}
//  while NVMCON.15 = 1 do ;
  
  while NVMCON.15 = 1 do
    nop;
    
  {This code could be compiled}
  repeat
  until NVMCON.15 <> 1;

  {I prefer this. But not so different.}
  while NVMCON and $8000 = $8000 do
    nop;

  {use lib}
  while  TestBit(NVMCON, 15) do
    nop;

  {Maybe fastest. but something funy}
  asm
    uniqLabel:
    BTSC NVMCON, 15; why not #15?
    GOTO uniqLabel
  end;
end.

And then click View-View Assembly to see ".asm" file.
(for description, I add comment)

Code: Select all

;==================================
;ForumQuest.dpas,7 :: 		while NVMCON.15 = 1 do
$0106	$	ForumQuest_L_2:
$0106	$803B01			MOV	NVMCON, W1
$0108	$280000			MOV	#32768, W0
$010A	$608080			AND	W1, W0, W1
$010C	$2000F0			MOV	#15, W0
$010E	$DE0880			LSR	W1, W0, W1
$0110	$508061			SUB	W1, #1, W0
$0112	$3A0003			BRA NZ	ForumQuest_L_3, ForumQuest_L_3
;ForumQuest.dpas,8 :: 		nop;
$0114	$000000			NOP
$0116	$040106			GOTO	ForumQuest_L_2
$011A	$	ForumQuest_L_3:
:====================================
;ForumQuest.dpas,11 :: 		repeat
$011A	$	ForumQuest_L_6:
;ForumQuest.dpas,12 :: 		until NVMCON.15 <> 1;
$011A	$	ForumQuest_L_7:
$011A	$803B01			MOV	NVMCON, W1
$011C	$280000			MOV	#32768, W0
$011E	$608080			AND	W1, W0, W1
$0120	$2000F0			MOV	#15, W0
$0122	$DE0880			LSR	W1, W0, W1
$0124	$508061			SUB	W1, #1, W0
$0126	$320002			BRA Z	ForumQuest_L_9, ForumQuest_L_9
$0128	$	ForumQuest_L_10:
$0128	$040130			GOTO	ForumQuest_L_8
$012C	$	ForumQuest_L_9:
$012C	$04011A			GOTO	ForumQuest_L_6
$0130	$	ForumQuest_L_8:
;============================================
;ForumQuest.dpas,15 :: 		while NVMCON and $8000 = $8000 do
$0130	$	ForumQuest_L_12:
$0130	$803B01			MOV	NVMCON, W1
$0132	$280000			MOV	#32768, W0
$0134	$608100			AND	W1, W0, W2
$0136	$280001			MOV	#32768, W1
$0138	$510001			SUB	W2, W1, W0
$013A	$3A0003			BRA NZ	ForumQuest_L_13, ForumQuest_L_13
;ForumQuest.dpas,16 :: 		nop;
$013C	$000000			NOP
$013E	$040130			GOTO	ForumQuest_L_12
$0142	$	ForumQuest_L_13:
;============================================
;ForumQuest.dpas,19 :: 		while  TestBit(NVMCON, 15) do
$0142	$	ForumQuest_L_17:
$0142	$803B01			MOV	NVMCON, W1
$0144	$280000			MOV	#32768, W0
$0146	$608080			AND	W1, W0, W1
$0148	$2000F0			MOV	#15, W0
$014A	$DE0880			LSR	W1, W0, W1
$014C	$E00001			CP0	W1
$014E	$320003			BRA Z	ForumQuest_L_18, ForumQuest_L_18
;ForumQuest.dpas,20 :: 		nop;
$0150	$000000			NOP
$0152	$040142			GOTO	ForumQuest_L_17
$0156	$	ForumQuest_L_18:
:=============================================
;ForumQuest.dpas,24 :: 		uniqLabel:
$0156	$	UNIQLABEL:
;ForumQuest.dpas,25 :: 		BTSC NVMCON, 15; why not #15?
$0156	$AFE760			BTSC	NVMCON, 15
;ForumQuest.dpas,26 :: 		GOTO uniqLabel
$0158	$040156			GOTO	UNIQLABEL
;ForumQuest.dpas,27 :: 		end;

(If you not familiar with asm, it is not so bad idea to think that number of lines with leading $0***(PC) means speed.)

if

The goal is to achieve fastest respond time with fewer instructions.

Answer is in *.asm file.