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Implement a "wall clock" on the RM48HDK

Tim Mulder
Intellectual 600 points


I want to execute a certain task at a certain times on a portable device. Hence, I need to a "wall clock" and a way to suspend the device when the task is stopped to save battery time. I was thinking of aggresive power management to archieve the latter, but I have no clue what is the best way to implement the former. Should I use an external "wall clock" chip and count execution cycles from then on or do something completely different?

Thanks in advance!

Tim

  • 0
    TI__Guru**** 199096 points

    Hi Tim.

    I have forwarded your question to one of our experts. He will be responding you soon. 

    Thanks and regards,

    QJ

  • 0
    TI__Guru 68980 points

    Hi Tim,

    If you're trying to run off a battery, then you should go with an external wall clock chip that is designed for micro-power.  

    The RM4xx will need to be powered off if you are trying to get your system into the <1uA range.   RM46xx is built in a relatively high performance process and there leakage power even when clocks are shut off will be in the mA range, not uA.

    You could look at a purpose-built RTC chip,  TI makes a bunch of them.   Here is a link to the product folder for Real-time Clock devices.

    Alternatively you might consider an MSP430 microcontroller, which is capable of micropower.  There is an application report - Implementing a Real Time Clock on the MSP430  (a little dated, so you could check if there are newer devices).   Literature # is slaa076a in case the link doesn't work.    There is software that comes with the app report, so you wouldn't be starting from scratch.

    Also, if you are using Code Composer Studio or IAR both products are supported so you don't need to add another IDE environment to your tool set.

    (Note IDE vendors: please forgive me if I missed any other IDEs that support both MSP430 and RM46xx; or better yet - add a note if your IDE supports both processor families).

    This approach is probably a little more work than using a purpose-built realtime clock chip.   But it gives you a programmable platform that can be used to respond to events even when your system is powered down.  And it gives you a chip that can also manage switching on and off the power rails of the RM46xx.   Also could provide you things like extra GPIO,  extra Analog inputs, or additional 'flash' or even FRAM for storing "EEPROM" like parameters... all depends on which MSP430 you would use. 

    Best Regards, Anthony