Count instruction cycle of assembly - Electronic Circuits Projects Diagrams Free

tinhnho · 28th February 2007, 09:31 PM

Code:

main: clrf count
      movlw 0x23
      movwf bdata
loop: rrcf bdata,f
      btfsc STATUS,C
      incf count
      movf bdata,w
      bnz loop

cycle for :
clrf = 1
movlw = 1
rrcf = 1
btfsc = 1 or 2
incf = 1
movf = 1
bnz = 1 or 2

The number cycles for that code is 39 cycles. Can anyone check it if this is right ? thanks

Pommie · 28th February 2007, 10:44 PM

The execution time for the code will be longer due to the fact that it loops and so some sections get repeated many times. Trying to work out the timing manually would be very difficult due to the fact that the bnz instruction can be branching dependent on the outcome of two different instructions (the rrcf and inc) [Edit, actually just on the value of bdata which is dependent on count]. If you copy the code into MPLAB, set the processor to 18Fxxxx and use the stopwatch, then MPLAB will work it out for you. That really is a horrible bit of code. Looking at it again, I think you will end up with 2 different values dependent on whether the Carry flag was set prior to calling it.

Mike.

Pommie · 28th February 2007, 11:24 PM

Woops, just realised you have counted the loops. I make it 38 if carry clear and 56 if carry set.

Mike.

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28th February 2007, 09:31 PM	(permalink)
tinhnho	Count instruction cycle of assembly Code: main: clrf count movlw 0x23 movwf bdata loop: rrcf bdata,f btfsc STATUS,C incf count movf bdata,w bnz loop cycle for : clrf = 1 movlw = 1 rrcf = 1 btfsc = 1 or 2 incf = 1 movf = 1 bnz = 1 or 2 The number cycles for that code is 39 cycles. Can anyone check it if this is right ? thanks

28th February 2007, 10:44 PM	(permalink)
Pommie	The execution time for the code will be longer due to the fact that it loops and so some sections get repeated many times. Trying to work out the timing manually would be very difficult due to the fact that the bnz instruction can be branching dependent on the outcome of two different instructions (the rrcf and inc) [Edit, actually just on the value of bdata which is dependent on count]. If you copy the code into MPLAB, set the processor to 18Fxxxx and use the stopwatch, then MPLAB will work it out for you. That really is a horrible bit of code. Looking at it again, I think you will end up with 2 different values dependent on whether the Carry flag was set prior to calling it. Mike. Last edited by Pommie; 28th February 2007 at 11:12 PM.

28th February 2007, 11:24 PM	(permalink)
Pommie	Woops, just realised you have counted the loops. I make it 38 if carry clear and 56 if carry set. Mike.