SysCtlClockFreqSet vs. SysCtlClockFreqGet

Kim Sandström

Other Parts Discussed in Thread: TM4C129ENCZAD

I have the following code on TM4C129ENCZAD:

    // Set the clocking to run directly from the external crystal/oscillator. 12 MHz external oscillator
    setclock = SysCtlClockFreqSet(SYSCTL_XTAL_12MHZ | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN, 12000000);
    SystemClock = SysCtlClockGet();

The hardware has an 12 MHz oscillator connected to OSC0 and OSC1

Upon executing the code setclock is set to 12000000 and SystemClock is set to 9600000.
What does this mean? My intent is to have a system clock directly from the oscillator at 12 MHz. I don't want to use the PLL.

over 10 years ago

0 Robert Adsett over 10 years ago

Guru 27665 points

In this case it means that SysCtlClockGet does not work on your processor. The library really needs to be updated to trigger an error in this case.

Robert

0 Amit Ashara over 10 years ago in reply to Robert Adsett

TI__Guru**** 244400 points

Hello Robert

A compilation error may be possible as we discussed a few weeks back.

Regards
Amit

0 peter lo1 over 9 years ago in reply to Amit Ashara

Intellectual 270 points

Hello Gents,

In the case with using the TM4C129, how does one go about reading back the system clock value that is CURRENTLY set, without altering it? According to the tivaware API the SysCtlClockFreqSet does return the system clock value, but it is based on the NEW value passed to it as an argument and not the current.

Thank you.

0 Amit Ashara over 9 years ago in reply to peter lo1

TI__Guru**** 244400 points

Hello Peter,

Yes, that is correct.

Regards
Amit

0 peter lo1 over 9 years ago in reply to Amit Ashara

Intellectual 270 points

Hello Amit,

Does this mean that the current tivaware API does not support reading back of the system clock value for a TM4C129 device? I am currently looking for a way to do so and wanted to get some advice on the best way to do this.

Thank you.

Regards,

0 Amit Ashara over 9 years ago in reply to peter lo1

TI__Guru**** 244400 points

Hello Peter

No, it does not. What is typically done is to store the return value of SysCtlClockFreqSet in a global variable and then use it in all functions that require a knowledge of the system clock frequency

Regards
Amit

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SysCtlClockFreqSet vs. SysCtlClockFreqGet