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CCS/EK-TM4C129EXL: EK-TM4C129EXL : delay time

B.M
Expert 1660 points
Part Number: EK-TM4C129EXL
Other Parts Discussed in Thread: EK-TM4C1294XL

Tool/software: Code Composer Studio



could anyone explain how to achieve 100,500,1000 ms delay time . for this 120MHz clock.




   g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                             SYSCTL_OSC_MAIN |
                                             SYSCTL_USE_PLL |
                                             SYSCTL_CFG_VCO_480), 120000000);




  • 0
    TI__Guru 72500 points

    Do you want a delay, or do you really want to do an operation every 100ms, every 500ms and every second? If it is the first, look at using the TivaWare function SysCtlDelay(); SysCtlDelay(40000000); will delay 1 second. SysCtlDelay(20000000); will delay 500mS . SysCtlDelay(4000000); will delay 100ms. 

    It is more common that you need to execute periodic tasks. You can use timers to generate periodic interrupts. You can use a single timer to generate an interrupt every 100mS. In that interrupt routine you can set a flag to do your 100mS task. Also increment and check a 500mS counter. Every 5th interrupt reset that count and set the flag to do your 500mS task. Likewise you can set a flag for your 1 second task every other time you do the 500mS task. Or you can use three timers, one set for 100mS, one for 500mS and the third for 1 second. See the TivaWare example in:

    C:\ti\TivaWare_C_Series-2.1.4.178\examples\boards\ek-tm4c1294xl\timers

  • 0 in reply to Bob Crosby
    Expert 1660 points

    Thanks Bob Crosby for your kindness.

    sorry about my silly question but how did you calculate the delay time .the clock is 120MHz .how SysCtlDelay(40000000); will delay 1 second . how did you calculate this value 40000000

  • 0 in reply to B.M
    Guru 92251 points

    AHMAD_OBAI said:
    how SysCtlDelay(40000000); will delay 1 second . how did you calculate this value 40000000

    From the documentation for SysCtlDelay in TivaWareTM Peripheral Driver Library USER’S GUIDE SW-TM4C-DRL-UG-2.1.4.178.pdf:

    I.e. for a nominal 1 second delay with a 120 MHz clock the delay count parameter for SysCtlDelay is 120000000 / 3 = 40000000.

  • 0 in reply to B.M
    Guru 117855 points

    Both earlier arriving posters have advised well.

    That given - it may prove useful to note the following:

    • the 'SysCtlDelay()' function (as poster Chester detailed) is 'Not' a high accuracy function - & is subject to error.    (error depends upon other program operations which are of higher priority (especially interrupts) which may 'Prolong' the length of your chosen delay).    
    • as vendor's Bob noted - the use of one of the (many) MCU Timers enables far more accurate delay (or timed interval) creation.

    Note too that while your program is executing 'SysCtlDelay()' - it is (almost) completely 'blind to & unable to perform' other program operations!    (higher priority interrupts escape this weakness)     This serves as the 2nd main reason while use of a 'Timer' proves (most always) a superior choice.    (i.e. Use of the Timer does not preclude other code from executing - while the Timer counts!)    When the Timer extinguishes (ends) - a timer interrupt is generated - and it is only then that you take your specific timer-based action...     This Timer usage thus proves far less 'disruptive' that (any) 'in-line, delay' - which periodically renders the MCU (near) 'deaf & dumb.'    Should your code regularly employ 'multiple calls to 'SysCtlDelay()' or to any 'in-line delay code' - your program may 'miss fleeting (very narrow) events' - while the MCU is 'trapped w/in the delay unwinding.'      Timers avoid such (unnecessary & unwanted) limitations...