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MSP432E401Y: What clock source is date/time derived from?

Brian S
Prodigy 180 points
Part Number: MSP432E401Y
Other Parts Discussed in Thread: MSP-EXP432E401Y

From what clock source is the date and time derived from (and incremented by)? For example, if I use (POSIX) clock_settime(...) to set the date/time to December 22 2020 11:00, and then 1 minute later I use clock_gettime(...) to retrieve the date/time (should be December 22 2020 11:01), what clock source does TI-RTOS use to do this? Does it use SYSCLK, counting the pulses so it can measure the passage of time? Or does it use the RTCOSC via the Hibernation module's external 32.768KHz crystal? If the latter then I wouldn't expect microsecond accuracy if I wanted to measure the difference between two events.

I'm using the MSP-EXP432E401Y LaunchPad kit, which has the MSP432E401Y microcontroller using a 25MHz crystal (PLL'd to 120MHz) and a 32.768KHz crystal, and running TI-RTOS.

  • 0
    TI__Expert 7015 points

    Hi, Brian, 

    I think the clock source is the RTCCLK which is Buffered version of the Hibernation module's 32.768-kHz clock.

    This can provide accuracy and stable real time clock with external crystal. 

    32.768kHz is about 30.5us per cycle. Why do you think it cannot have microsecond accuracy? 

    Thanks, 

    Lixin

  • 0 in reply to Lixin Chen1
    TI__Expert 7015 points

    Hi, Brian, 

    32.768kHz is good enough for date/time clocking. The accuracy can be 30.us that mean no problem for milisecond accuracy. 

    If you need to get microsecond accuracy, there are two ways: 

    (1) MOSC (5MHz~25MHz) with external crystal on OSC0 pin and OSC1 pin. 

    (2) PIOSC (16MHz) with software trimmed by 32.768kHz crystal on XOSC0 pin and XOSC1 pin. 

    Either MOSC or PIOSC can be used as PLL reference clock source, and PLL output clock can be used as SYSCLK which can be configured up to 120MHz. 

    Thanks, 

    Lixin