waking up from sleep using timer1.

[ch_dupre]

Hello,

I am trying to put the PIC to sleep and wake it up using TIMER1. I've been using the WDT timer in the past but I'd like to have a better accuracy using TIMER1.
I'm using a PIC18LF2620
CCS v4.033 and also V3.249

I can observe 2 things:
1: If the timer value is 0xFB00 or more, I can't see the PIC going to sleep, and the message: "Wakeup on T1\n" from the isr isn't printed on the serial port. On the other hand, the while loop keeps going.

2: if the Timer value is less than 0xFB00, the PIC goes to sleep but never wakes up.

Here is my code:
Main.c

[Ttelmah]

Comment one.
The interrupt code, will _only_ get executed, if both the interrupt is enabled, and the global interrupt flag is set. Without the global flag, the interrupt will only wake the chip. 3.5.1 in the data sheet.
Second, if the interrupt handler is not called, it becomes _your_ responsibility to clear the interrupt flag. You need to do this before sleeping, or the code will never wake. You should do this anyway, otherwise if the flag is set, the CPU will not go to sleep.
In the 'setup_timer' version, you want:
setup_timer_1(T1_DIV_BY_8 | T1_EXTERNAL | T1_CLK_OUT);
Given external input, output, to form the oscillator, and the division by eight.
Get rid of the IESO fuse. This will imply, that because the T1 oscillator is running, you will almost certainly _not_ see messages printed just after wake up. With this set, the chip will wake up immediately from sleep, without waiting for the main oscillator to start. It'll run the first few dozen instructions, at the speed that T1 is running, not the master clock. This means that any serial print done here, wll just result in garbage. Lok at 23.3.1 in the data sheet. The delay in the interrupt, will probably avoid this, but it is a danger.
Get rid of the delay in the interrupt routine. Since delays are used in both the interrupt code, and also the main, this will result in interrupts automatically being disabled in the main, wherever delays are used. On sleep, the instruction immediately after the sleep, is 'prefetched', and in some cases, may actually be partially performed, before the sleep is entered. This could really screw things up...
[code]
#INT_TIMER1
void timer1_isr(void) {
fprintf( COM2, "Wakeup on T1\n" );
}

void main()
{

//setup timer just once
setup_timer_1(T1_DIV_BY_8 | T1_EXTERNAL | T1_CLK_OUT);
while ( 1 )
{
//ensure any print from the interrupt has completed
delay_ms(30);
fprintf( COM2, "Sending to Sleep\n" );
set_timer1(0xF000);
clear_interrupts(INT_TIMER1);
enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);
sleep();
//ensure the prefetched instruction is nop
delay_cycles(1);
delay_ms( 500 );
}
}

Best Wishes

[ch_dupre]

Thanks Tthelmah.
I've modified my code to :

[kevcon]

What crystal frequency are you using?

You are making it more complicated than it needs to be, look at the code on this page

http://www.ccsinfo.com/forum/viewtopic.php?t=31822&postdays=0&postorder=asc&start=15

The LED will be on for 2 seconds and off for 2 seconds.

[ch_dupre]

I'm using a 20MHz crystal, and a 32,768KHz oscillator connected on RC0.

Christophe D.