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machine cycles

 
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Bilal



Joined: 24 Apr 2010
Posts: 75
Location: Islamabad

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machine cycles
PostPosted: Sun Oct 31, 2010 7:36 am     Reply with quote

hi.. i want to know how can i calculate proper time of execution of instructions in ccs c.. as we can do in assembly language (with machine cycles)
thanks
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temtronic



Joined: 01 Jul 2010
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Location: Greensville,Ontario

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PostPosted: Sun Oct 31, 2010 7:42 am     Reply with quote

Once you've compiled a working program, printout the listing (filename.lst).

draw a couple of vertical lines down the right side

in this new 'column', write the machine cycles for that line, usually 1, 2 if a compare-branch instruction. Details are in the 'instruction set' info.

add the column up and you have the total machine cycles.

time to execute this code depends upon processor,crystal used, any PLL info, etc.

hth
jay
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Sun Oct 31, 2010 9:27 am     Reply with quote

Or just put the code into a simulator like MPLAB, add a couple of markers, and let the stopwatch do the work for you.
This has been answered before, and a search here should find more detailed replies, but the big problem is that quite simple single instructions, can have dozens of different timings, dependent of 'circumstances'. Where values have to be retrieved from, the types of the values involved, whether the same numbers are used 'nearby', so can be retrieved from temporary storage, or need to have their locations 'calculated' first, etc. etc.. You will probably find that the total time for a simple addition, could vary from just a couple of machine cycles, to perhaps 600 machine cycles (floats retrieved from an array).....

Best Wishes
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Sun Oct 31, 2010 2:59 pm     Reply with quote

Here is the post that Ttlemah referred to, which explains how to use the
stopwatch feature in MPLAB:
http://www.ccsinfo.com/forum/viewtopic.php?t=38351
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