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TM4C internal clock configuration

sachin gole
Prodigy 140 points

Hi All,

I have developed my board with TM4C123, I have flashed it using XDS100v2-ARM.

I can see that LED toggling code is working good.

When I tried to get clock it in debug mode it shows

SysCtlClockGet = 0x0000077C which is 1916 Hz, why it is too low ?

I dont have any external oscillator connected on board. I wanted to set something around 50 MHz.

SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_INT);

are these parameters correct ?

  • 0
    Guru 55913 points
    Value seems odd (SYSCTL_XTAL_16MHZ) when clock source you like to be internal driven precision oscillator (PIOSC) and no XTAL is present.
  • 0
    TI__Guru**** 244400 points
    Hello Sachin,

    The parameters are right. Can you read the variable that is being updated with the value of SysCtlClockGet?
  • 0 in reply to Genatco
    Prodigy 140 points

    Thank you for suggestion.

    I don't have external clock connected on board. I am looking for stable clock source. Can you please suggest better value which will give know result in frequency which I wanted to generate PWM.

    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16_3MHZ | SYSCTL_OSC_INT);

  • 0 in reply to Amit Ashara
    Prodigy 140 points

    Are you sure, because I can see that API explanation says.

    #define SYSCTL_XTAL_16MHZ       0x00000540  // External crystal is 16 MHz

    Where I wanted to set  internal driven precision oscillator (PIOSC) and no XTAL is present.

    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_INT);

  • 0 in reply to sachin gole
    Guru 55913 points

    >I don't have external clock connected on board.
    Sounded like you were referring, last post see you confirmed Amit indeed No XTAL and No external clock source on custom PCB.

    It would seem to me you may need call (SysCtlAltClkCfg) to also assign peripherals an alternate clock source. Perhaps you can use the internal PIOSC with PLL but check TM4C123 data sheet as there may be some restrictions.

  • 0 in reply to sachin gole
    TI__Guru**** 244400 points
    Hello Sachin

    When you use SYSCTL_OSC_INT, the source clock frequency is hardcoded as 16MHz. You can check the SysCtlClockSet API to see how it is programmed.