PIC24E and RTC

championx · Joined: 28 Feb 2006 Posts: 151

Hi! I'm starting with pic24, and i have a simple question, is there a way to use the RTC module (with a 32khz crystal) and generate a 1 second interrupt on timer1 or any other timer?

Sorry, but I'm trying with this config:

Ttelmah · Joined: 11 Mar 2010 Posts: 19490

The 'standard' way, is just to set bit15 in the timer counter, inside the interrupt. This jumps it forward 32768 counts, so you get a 1 second tick.

championx · Joined: 28 Feb 2006 Posts: 151

Hi Ttelmah, thanks for your answer, i have worked on the program and discovered that this settings are "restarting" the pic every once in a while...

If i comment this line:

Ttelmah · Joined: 11 Mar 2010 Posts: 19490

The obvious reason is something you are doing in the interrupt.

I'd suggest you need to implement an error trap routine. A search here will find how to do this. My guess would be that your interrupt is causing either an address error trap, or a stack overflow. Possibly an address into an array that goes too far at some point in time, or a stack that is close to the limit, and results in an overflow, when the interrupt just happens to occur at a point in the main code with more data already on the stack.

jeremiah · Joined: 20 Jul 2010 Posts: 1344

Just wanted to toss out that an optional way of setting the 1 second is in setup_timer1(). There is an optional second parameter that lets you specify the period in most PIC24 chips

If you do the following:

championx · Joined: 28 Feb 2006 Posts: 151

Hi Ttelmah, the interrupt just toggles a pin... nothing else... just output_toggle(LED_PIN)

When i read the restart cause it is: RESTART_TRAP_CONFLICT

Do you know why is that? The code is really simple.

Ttelmah · Joined: 11 Mar 2010 Posts: 19490

Restart_cause only tells you that the restart was caused by an error trap. Not what the trap 'was'.

The point is that if you instead create a trap interrupt routine, then this will be called instead of restarting. You can then 'snapshot' the memory address that actually triggered the restart. How to do this is described here in the forum. Also, the trap interrupts are split into a series of separate ones, so there is 'ADDERR', 'STACKERR', and 'MATHERR', allowing you straight away to 'narrow down' the actual cause.

However my guess would be a stack overflow. Calling the interrupt takes a lot of stack space. What compiler version are you on?. There was a problem a while ago, with the default stack size being too small, for even quite basic programs.

Add:

#build(stack=512)

Up at the top of your program (up with the fuses).

If the problem disappears, then you have your answer.

If the compiler is old, try with stack=256 (the current default).

Some maths operations use a lot of stack. If you have a few subroutines (more on the stack), and the interrupt happens to be called from inside one using some maths, then running out of stack is easy. If your compiler is a little old, the default was 128, and this could run out, for simple things like an interrupt inside a print routine....

championx · Joined: 28 Feb 2006 Posts: 151

Thanks Ttelmah, that did the trick! it was the stack.