timerafter

[omega7]

Hi all,

My question concerns the using of the timerafter event. I suspect that the event sometimes is fired unintentionally.

Here is the code:

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case (enableTimer > 0) => detectTimer when timerafter(actualTime + USEC(3650)) :> void:

The code is a kind of watchdog. When a signal isn't toggling on a port for more than 3650 us, the timer should fire the event:

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case detectPort when pinsneq(portLevel) :> void:

detectPort :> portLevel;

detectTimer :> actualTime;

The problem is that the timer seems to fire now and then, while the toggle signal on detectPort is still there.

Can someone explain what happens when the (actualTime + USEC(3650)) overflows the unsigned size ?

Are there other causes than may explain the problem?

Thanks!

Martin

[bsmithyman]

I'm not totally sure what's going on, but with the way you've written it the compiler is going to have to do some thinking, so it might be possible to make it more explicit. Instead of putting the line "timerafter(actualTime + USEC(3600))" you could try using "timerafter(triggerTime)" as the guard and setting the delay in your pin toggle case, i.e. "triggerTime = actualTime + USEC(3600)". As it stands, I'm not sure what the compiler does when you have an evaluated statement in the guard. It might try to be smart and prevent the overflow (when really you do want the overflow to happen, just before you set the event).

Cheers,
Brendan

Edit: Fixed unresolved parentheses.

[segher]

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case (enableTimer > 0) => detectTimer when timerafter(actualTime + USEC(3650)) :> void:

Show that USEC() macro?

[omega7]

The USEC Macro? Here it is!

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#define USEC(x)		(x*100)

[segher]

If your actualTime variable is unsigned, overflow is not a problem (it will wrap);
if it is signed, in C, that is undefined behaviour (but it will still work in XC I think).

It will also work fine on the xcore timer, there is no overflow there.

You'll have to show more of the code, and/or investigate better when exactly
this happens.

Good luck,


Segher