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rdp

using timer event to wake from low power mode

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(Context: I'm an experienced embedded systems engineer, just dipping my toe into MSP430-land.  My target system is an MSP-EXP430FR5994 LaunchPad dev board.)

General goal: How do I wake the processor N ticks in the future, where one tick is 1/32768 second and N can be as large as 2^15?

My first thought was to use the RTC, but that appears to have a resolution of 1 second. 

My second thought was to use a timer module (e.g. TA1) and use its compare interrupt to wake the processor from LPM4.

So my questions:

  1. Is there a better / alternative way to wake the processor N ticks in the future?
  2. Table 6-1 ("Operating Modes") states that a "COMP" event can wake the processor from LPM4.  Does "COMP" refer to a compare interrupt from a timer?
  3. Is there a block diagram of the counter module(s) somewhere?  I didn't see it in the processor-specific datasheet.

 

 

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update: I (finally) found rtc_[ab].h and noticed that the RTC provides a 32 bit counter mode. 

My favorite solution would be to run the RTC continually in 32 bit mode and use a compare function to wake it from LPM3.5.

I see that a calendar match will wake the processor, but is there a way to:

  • run the RTC at 32678 Hz rather than at 1 Hz? (I think yes)
  • set the comparison register directly as a 32 bit value rather than as year/month/day/hour/minute/second?

 

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11 hours ago, rdp said:

and use its compare interrupt to wake the processor from LPM4.

LPM4 can be problematic.  There is a bit you can set to enable ACLK in LPM4, but the default is for the clock to be off, and of course, the cpu is off.  If I read the docs correctly, in LPM4 if ACLK is enabled, it uses the VLO as its source, approx. 10KHz, and is susceptible to temperature.  See Table 3-2. System Clocks, Power Modes, and Clock Requests in slau367p.pdf

For a quick read on the RTC take a look at slap113.pdf

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