PIC24EP512GP806 - Timer interrupt while sleeping

[benoitstjean]

Device: PIC24EP512GP806
Compiler: 5.116

Good evening,

I never attempted this but I'd like to put my entire device to sleep but keep timer 1 interrupt active. Is this possible? If so, then what happens with the main() code where the interrupt is really handled (that's how I do it anyhow...)?

Not sure how you guys do it but in my timer 1 ISR, really, all I have are a bunch of flags that are checked and if set, increase a counter and exit. That's it. So in this timer ISR, I have like 20 different counters that I use mainly for delays and timeouts. This way, the ISR is entered and exited as quickly as possible and leaves the main do the hard work where I have a simple while loop that checks the count value of the counters and when they reach a certain value, execute the code for that counter.

Example:

[benoitstjean]

UPDATE: I guess the only way is to use SLEEP_IDLE because I am using setup_timer1( TMR_INTERNAL | TMR_DIV_BY_1 ); and don't have an external oscillator?

Using SLEEP_IDLE, it drops in half from 22mA to around 11-12mA. This is pretty decent.... but feel free to provide more suggestions if you think I can take it down even lower.

Thanks again!

Ben

[Ttelmah]

You are missing one key thing.
PMD.

This chip allows you to switch on/off each peripheral separately. So you do
need to use the IDLE mode, but you can reduce what is drawn in this by
switching off the other parts you don't need. This is controlled by PMD
(Peripheral Module Disable). You set bits in the PMD registers to turn off
the modules you are not using. This stops their clock.
Look at section 10.4 in the data sheet.
Unfortunately there are so many bits (50+), that you have to work out
for yourself the pattern needed to leave just what you want running, and
(of course), need to clear the bits when you want to power back up. However
with these you can individually control which parts of the chip are actually
powered.

[benoitstjean]

Hi,

Yeah, I already have the following below that you had given me years ago and it worked for what I was doing at the time which required that particular circuit to go in full sleep but this new thing I'm working-on requires me to be able to wake-up the device once in a while....

// Disable all peripherral power
#byte PMD1 = getenv("byte:PMD1")
#byte PMD2 = getenv("byte:PMD2")
#byte PMD3 = getenv("byte:PMD3")
#byte PMD4 = getenv("byte:PMD4")
#byte PMD5 = getenv("byte:PMD5")
#byte PMD6 = getenv("byte:PMD6")
#byte PMD7 = getenv("byte:PMD7")

PMD1 = 0xFF;
PMD2 = 0xFF;
PMD3 = 0xFF;
PMD4 = 0xFF;
PMD5 = 0xFF;
PMD6 = 0xFF;
PMD7 = 0xFF;

I guess timer 1 is T1MD - bit 11 of PMD1 register.

But as for the coding goes with respect to my explanation, let's say the timer 1 interrupt is available, while the device is sleeping in idle mode, where should the code be executed? I mean, if the device is sleeping, I would guess that the main() is not running, correct?

If this is the case, then does this mean that the only thing ticking is the timer interrupt? If yes, then I guess I'd need a special piece of code in there that runs only when the device is sleeping? Because as I explained in my initial message, the timer 1 interrupt, when the device runs normally, only increases a variable for a given "timer" if that timer is enabled though the TimerX.IsActive flag.... so TimerX.Count ++.

Then the code for that timer is executed in the main() with if( TimerX.Count == some_value ) {execute code}.

So if the main is not running, then that code needs to be in the timer interrupt directly under a special condition if( Device.IsSleeping == true ) {execute_this_code}.

Does this make sense?

Thanks again!

Ben

[jeremiah]

I use timer1 to wake from full sleep (not just idle) on all of my PIC24 projects. The key is that timer1 needs to be using an asynchronous external clock (like a 32khz crystal oscillator for example) or an internal LPRC clock

If you are trying to wake up the timer with the standard internal clock it won't work unless your chip has an internal LPRC clock that timer1 can access as a clock source (varies by chip). Note that these LPRC clocks are generally pretty imprecise (large tolerance often times)

Here is an example setup for an external 32khz clock connected to a pic24FJ256GA406

[Ttelmah]

and the code remains wherever it was when you called the sleep. It will
jump to the ISR if the interrupt is enabled, and when the ISR exits
return to the main code.

[jeremiah]

Now that I have had some time to look at your chip's datasheet and the CCS header file, it looks like your only options for waking up from sleep on a timer involve some sort of external clock source tied to the pin T1CK.

Below is some basic test code for a 32khz crystal oscillator:

[temtronic]

outside the box thinking....
..could you add a RTC module ? Those you can program for say 1 interrupt per minute(depends on device of course ). Usually projects 'need' to have a clock on display so a battery backed, external RTC severs several purposes.