Atmeg8 clock check on Simulator

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Ahmed.ben.kamal
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Posted by Ahmed.ben.kamal: Tue. Oct 3, 2017 - 03:51 PM
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i newbie in avr programming and i faced strange behavior to me during  i made very simple program to check the cycle of  program execution 

 

As you can see from the snap shot of Code during execution then paused when reached the Braking point  that the Cycle Counter is "458789" in processor status  but as per code "while loop" will be exist when "CyclesNo" variable will "65535" so i expect that when Cycle Counter in processor status reached  to "65535" should also "CyclesNo" variable  reached to "65535"

 

but what happen when "CyclesNo" = 65535  the Cycle Counter is "458789" in processor status

 

 

Please advise 

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AVR Microcontrollers, megaAVR and tinyAVR
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awneil
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Posted by awneil: Tue. Oct 3, 2017 - 03:57 PM
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The 'Cycle Counter' shown in the 'Processor Status' window at the left of your screen is CPU cycles - it has nothing to do with your 'C' variable called 'CyclesNo'

 

Each turn of your high-level 'while' loop will take more than one CPU cycle!

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clawson
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Posted by clawson: Tue. Oct 3, 2017 - 05:02 PM
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As Andy says there isn't a one to one relationship between C statements and machine cycles. Your using a 16 bit counter which occupies two AVR registers so both the increment and the check in the while loop will take multiple instructions and multiple CPU cycles. This is a RISC CPU so something that looks simple in C could take loads of the simple opcodes.

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kk6gm
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Posted by kk6gm: Wed. Oct 4, 2017 - 04:09 AM
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You should single-step through your loop a few times to get an idea of the relationship between CPU cycles and your variable's changing values.

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awneil
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Posted by awneil: Wed. Oct 4, 2017 - 07:39 AM (Reply to #4)
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and look at the disassembly ... 

Top Tips:

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  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillator: https://www.avrfreaks.net/comment...
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Ahmed.ben.kamal
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Posted by Ahmed.ben.kamal: Wed. Oct 4, 2017 - 08:03 AM
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 really  thanks so much  i got a lot of information from your posts 

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awneil
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Posted by awneil: Wed. Oct 4, 2017 - 08:10 AM (Reply to #6)
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You're welcome.

 

So, when you said, "i newbie in avr programming" - I take it that means you're a newbie with programming in general?

 

The difference between the statements in a high-level language (such as 'C') and the low-level machine/CPU instructions is entirely general - not specific to AVR.

 

The higher the level of the source language - and 'C' is relatively "low-level" compared to many (most?) these days - the greater the disconnect from the underlying machine level.

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillator: https://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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