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PM_DEEP_SLEEP_COUNT = 0x6A75?

Orjan Friberg
Expert 1385 points

Hi,

I'm trying to understand the 0x6A75 value in the DSCOUNT field of DEEPSLEEP_CTRL. Our board uses a 19.2 MHz oscillator as opposed to the more common 24 MHz one.

Based on my experminentation, 0x6A75 == 27253 corresponds to a delay of 5.68 ms, indicating that it's actually counting at a frequency of MOSC/4 == 4.8 MHz.  For a 24 MHz oscillator, the same number of cycles would amount to a 4.54 ms delay, which seems excessive; I would expect a value in the ballpark 1 - 1.5 ms.

Where does the 0x6A75 value come from, and is the "excessiveness" there to cover temperature changes, process variations, different manufacturers etc?

Thanks,

Orjan

  • 0
    Expert 1385 points

    Found this answer over at the Sitara forum:

    Oscillator start-up time depends on many product specific variables like the crystal circuit components, PCB layout, and operating conditions. Therefore, it is not possible to provide a maximum value for this parameter.

    System level characterization of the product across all operating conditions would need to be performed to determine the maximum oscillator start-up time.

    http://e2e.ti.com/support/arm/sitara_arm/f/791/t/332473.aspx

    So regardless of where 0x6A75 comes from we'll need to do our own measurements on this.