Timing Error with 12F629

[Dick Ivers]

Code as follows:

i var byte
time var byte
counter var word

time = 40 '(40 second run time)

for i = 1 to 10
counter = 0
while counter < time*500 '(40*500*10 = 200,000)
GPIO.4 = 1 '(75% duty cyle)
pauseus 150 '(pwm = 5000 hz (.000200 sec. period))
GPIO.4 = 0
pauseus 50
counter = counter+1
wend
next

[Archilochus]

HI Dick,
Have you checked the oscillator DEFINES, etc?

Arch

[Dick Ivers]

Hi Arch,

I forgot to mention that the 12F629 is running with the internal 4 mhz oscillator. Set by configuration: @device intrc_osc_noclkout.

Dick

[Bruce]

Hi Dick,

94 seconds is about right. If you run this through MPLAB with a breakpoint
set on NEXT, you'll see it takes 9.4 seconds total just to reach NEXT.

Run through 10-times, and you end up with around 94 seconds to complete
your 10 pass loop.

You're forgetting to add-in the over-head for PBP commands.

for i = 1 to 10
counter = 0
while counter < time*500 '(40*500*10 = 200,000)
GPIO.4 = 1 '(75% duty cyle) 
pauseus 150 '(pwm = 5000 hz (.000200 sec. period))
GPIO.4 = 0
pauseus 50
counter = counter+1
wend
next ' <-- Takes 9.4 seconds to get here the first time

Try it with these changes for around 40.0366 S.

Time = 29
while counter < time*493

[Dick Ivers]

Dear Bruce,

Thanks for your response and your astute trouble-shoot of the problem. The suggested fix does work.

I had a suspicion that code execution time was the culprit, but had no way of checking for the overhead time. I am surprised that it adds to so much error. I gotta get some tools to do that kind of debugging. Isn't MPLAB an assembly language code development suite?

Thanks,

Dick

[mister_e]

Under MPLAB, you can include language suite. See Melabs website to get the patch and procedure for that

click here

[Bruce]

Hi Dick,

Thanks for your response and your astute trouble-shoot of the problem. The suggested fix does work.

I had a suspicion that code execution time was the culprit, but had no way of checking for the overhead time. I am surprised that it adds to so much error. I gotta get some tools to do that kind of debugging.

You're very welcome.

Isn't MPLAB an assembly language code development suite?

Not at all. MPLAB works with most C compilers, PBP & PBC. It's a de-bugging/learning tool for the PIC. It's also free. My favorite price..;o]

I highly recommend anyone using the PIC get familiar with MPLAB. It can save you countless hours of head-banging.

FYI: PBP uses a library. Even simple BASIC commands like serin, pulsout, count, while/wend, for next, etc, will generate many lines of code in assembly language. Some will generate "pages" of asembly code depending on the complexity of the command/library routine.

With MPLAB you can see all of this, and get a better idea of the over-head & time it takes for certain BASIC library routines (BASIC commands) to execute.

Here's how to install & set MPLAB up with PBP:
http://www.microengineeringlabs.com/support/mplab.htm

TIP: Get familiar with setting breakpoints & using the stopwatch to see how long PBP commands take to execute. Very handy stuff, and definitely worth the effort.

This particular problem/scenario is a prime example of why it's handy to learn to use MPLAB.