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Timer Capture Tiva TM4C123GXL

Zhen Wei Ng
Prodigy 50 points

Hi,

I'm currently using TIVA TM4C123GXL. I'm trying to create a code whereby example; when x = 0, I start a timer, and when x = 2000, I stop the timer. Then get the duration of how long it takes for x to reach 2000, and use it for something else.


Can someone enlighten me on how to do this? Thanks.

  • 0
    Guru 26105 points

    Hi, 

    See this thread for a similar request or search the forum first:

    http://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/p/327659/1141047.aspx#1141047

    Petrei

  • 0 in reply to Petrei
    Prodigy 50 points

    Hi Petrei,

    I've looked through the thread but I don't really understand the code. I've tried putting the code in to find the number of cycles but the number I get is 0.

  • 0 in reply to Zhen Wei Ng
    Guru 26105 points

    Hi,

    There is a hidden register inside micro, cycle counter, which allows to count the number of elapsed cycles between a start command and a stop one, if the cycle counter was enabled. The cycle counter is 32 bits long, so at 80 MHz maximum time (before overflow) is around 53 seconds.

    Read all the posts in that thread, since some added declarations were revealed after the post with the code in blue fonts (depends on what you do - when I posted first i had already included some of the missing declarations). Maybe you are in the same situation.

    And depending on your real case, the procedure is: start command, set x=0, do another thing until x=2000 and emit stop command. Take into account what was done during x=0 and x=2000 if you want to be extremely precise.

    If you "measure" long time intervals and no need for accuracy, then an alternative is to start/stop a timer. 

    Petrei

  • 0 in reply to Petrei
    Prodigy 50 points

    Hi Petrei,

    Sorry for the late response. If I were to use a timer, how should I configure the Timer and what should I put in the Interrupt Handler?

  • 0 in reply to Zhen Wei Ng
    Guru 26105 points

    Hi,

    You may configure the timer as 16-bit or 32-bit periodic timer and in this case the resolution of measurement is the system clock period. For 16-bit periodic timer, it will overflow soon enough, so if your expected time intervals are more than overflow time, then you will need to configure the interrupt to count also the number of overflows. 

    You may play with the timer as you wish - even to use the built-in prescaler. 

    Petrei