PBP Using too many instructions

[The Master]

Hi, Im trying to optimise some of my code because its not running fast enough. Im trying to control PWM seperately on 24 pins. I did some tests to see what was taking so long and it seems to be the if statements.

IF 1=vPWMPos THEN
ENDIF

'Where vPWMPos is 1 the above code takes 7 instructions
'Where vPWMPos is not 1 the above code takes 8 instructions


'I also found out that the compiler does some clever optimisation
IF 1=1 THEN
ENDIF

'The above code uses no instructions at all because the compiler realises 1 will always equal 1

So, 7-8 instructions just for an if statement seems like quite a lot. Can anyone explain to me why it takes so many and if there is a away to optimise it at all.

TMR0 overflows after every 256 instructions. My if statements alone use 192 instructions. Add that to the rest of the code and it goes over 256 and this is only half the code i want to put in it. Using the prescaler isnt really an option either because that causes flickering

[Darrel Taylor]

... Can anyone explain to me why it takes so many and if there is a away to optimise it at all. ...

The WHY is 2 fold.
1. There's a CLRWDT in there. That can be eliminated with the NO_CLRWDT define.

2. PBP doesn't optimize Page switching as well as it does BANK switching. So before it can jump past the code (if the condition is false), it sets BOTH page bits, whether it needs to or not. And in most cases, it doesn't need to.

But even if you eliminated both of those issues with an ASM macro, it would still take 4-5 instructions, for a total of 120 cycles. Better, but not Best.

To really make it faster ... use the BRANCH or BRANCHL command. Then instead of 24 IF statements, it jumps right to the section it needs to be in, according to the the vPWMPos variable.

Branch will take about 16 instructions, BranchL will take a few more.
<br>

[The Master]

Thats interesting. Idealy i would like to get it down as far as possible. In this case the multiple if statements are required. It checks each pin's PWM value against the current PWM position. If it matches then that pin gets turned on. In my actual code i dont compare against a constant (1). Sorry for the confusion.

How would i go about doing the ASM macro thing?

Is there any other way to turn a pin on when a certain condition is met? I think this would probably work "pin = (pinValue=PWMPos)" but i wonder if that would get compiled to the same kind of code as an if statement.

Thinking about it, something like that would be an ideal solution. Whenever PWMPos overflows to 0 i have a seperate set of if statements that turn off any outputs whos values are less than 255. Both blocks of if statements are inside another if-then-else statement. If this method works then it should be able to do the whole thing with just 1 or 2 instructions

[Darrel Taylor]

... In this case the multiple if statements are required.

I have my doubts about that.
Multiple IF statements usually just means Spaghetti.

How would i go about doing the ASM macro thing?

Well, here's one way ...

;---------------------------------------------------------------------------
ASM
IfEqual  macro Bin, Cin, Lin          ; Bin is a BYTE variable
    RST?RP                            ; Cin is a constant to campare against
    movlw   Cin                       ; Lin is a label to jump to ...
    subwf   _vPWMPos,w                ;   if the condition is false
    btfsc   STATUS, Z
    goto    Lin
  endm
ENDASM
;-----[Here's how you use it]----------------------------------------------

@  IfEqual  _vPWMPos, 1, _L1
  ; code here executes if _vPWMPos = 1
L1:

@  IfEqual  _vPWMPos, 2, _L2
  ; code here executes if _vPWMPos = 2
L2:

In most cases, it will take 4-5 instructions.
But care must be taken to insure it doesn't cross a Page Boundary.

I still think you'll be better off using BRANCH.<hr>

I think this would probably work "pin = (pinValue=PWMPos)" but i wonder if that would get compiled to the same kind of code as an if statement.

That way only works if you can use the inverse of the result ...

myPIN = !(pinValue = vPWMPos)

Of course, the inverse of that is ...

myPIN = !(pinValue != vPWMPos)

[The Master]

Heres what my code looks like

IF vPWMPos=vPWM[0] THEN pA1=1
IF vPWMPos=vPWM[1] THEN pA2=1
IF vPWMPos=vPWM[2] THEN pA3=1
IF vPWMPos=vPWM[3] THEN pA4=1
IF vPWMPos=vPWM[4] THEN pA5=1
IF vPWMPos=vPWM[5] THEN pA6=1

Multiple ifs are needed because its possible for all of the vPWM values to be the same.

That ASM looks complicated but ill try and figure it out.

Im not at the PC i program on at the moment. Do you know if setting the value directly would work and if it does how many instructions it would take?

[Darrel Taylor]

That code is completely different from what you originally asked about.
Now you've got Array's involved.

When you get back to the PC, post what you have.
I'll take another look at the "Real" question.

But I still smell spaghetti.
<br>

[Art]

Heres what my code looks like

IF vPWMPos=vPWM[0] THEN pA1=1
IF vPWMPos=vPWM[1] THEN pA2=1
IF vPWMPos=vPWM[2] THEN pA3=1
IF vPWMPos=vPWM[3] THEN pA4=1
IF vPWMPos=vPWM[4] THEN pA5=1
IF vPWMPos=vPWM[5] THEN pA6=1

Multiple ifs are needed because its possible for all of the vPWM values to be the same.

Just looking at that, why not make the "pA" variables an array as well and just:

FOR  BLA = 1 to 6
IF vPWMPos=vPWM[BLA-1] THEN pA[BLA]=1
NEXT BLA

Otherwise I don't see how your claim that the array made things easier could be possible.