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TM4C129ENCPDT: HIB clock - external crystal not starting

David M. Alter
Guru 61235 points
Part Number: TM4C129ENCPDT
Other Parts Discussed in Thread: EK-TM4C1294XL

On  TM4C129ENCPDT device, customer is using a 32 kHz crystal across XOSC0 and XOSC1 in the HIB module.  From what I can tell in the device datasheet, this oscillator should start up on its own by default.

1) Is that correct? (that the oscillator should start up on its own)

2) If no, do you need to configure some register bits for it to start?  If so, which bits?

I attempted to test on the EK-TM4C1294XL Launchpad, which has a 32 kHz crystal across XOSC0/1.  Oddly, I am seeing about a 111 kHz oscillator at the crystal.  I used CCS to set the CLK32EN bit in the HIBCTL register, but it did not make a difference.

Thanks and regards,

David

  • 0
    TI__Guru**** 191906 points

    Hi Dave,

      Yes, the CLK32EN bit must be set for any hibernation clock source to be valid as well as for the hibernation module to be enabled. 

      Normally if you use the TivaWare then the CLK32EN setting is taken care by calling HibernateClockConfig(HIBERNATE_OSC_LOWDRIVE);.

    TivaWare library contains a hibernate module example. It can be found in <TivaWare_Installation>/examples/boards/ek_tm4c1294xl/hibernate folder. 

  • 0 in reply to Charles Tsai
    TI__Guru 61235 points
    Charles,
    Thank you. I got it working. Flip CLK32EN in CCS and the crystal starts. Reason I was seeing 111 kHz before was that I was looking at the wrong terminal on the crystal and just seeing noise that I was gaining up with the scope. The other terminal shows the 32 kHz signal (with larger amplitude than the other terminal) when CLK32EN=1.

    Regards,
    David