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I am getting an oscillator failure trap when I try to run some code on my dsPIC33FJ128GP804.

This has me very confused. I am using the FRC with a PLL to run the chip at 36.85 MHz.

I was always under the impression that an oscillator failure trap occurs only with crystal oscillators in certain conditions, and never with an on-board RC oscillator.

How could this be?

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1 Answer

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Are you really sure you are getting a oscillator failure trap? Just because it ends up in that trap routine doesn't guarantee it got there via the trap. Have you set a breakpoint at the trap location and examined the stack to see how it might have gotten there?

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Can you think of another way it could end up there? – Thomas O Jun 23 '11 at 17:42
Huh. You're right. INTCON1bits.OSCFAIL is not set. Now to figure out why it is ending up there...! – Thomas O Jun 23 '11 at 17:44
The only error is DMACERR, a DMA error. But I'm not using DMA... How weird...! – Thomas O Jun 23 '11 at 17:45
@Thomas: There are lots of ways of ending up in strange locations. On a dsPIC the most common are either W15 corruption or stack corruption, then doing a return. Also note that you don't know how many instructions got executed before it just happened to end up in your trap routine. – Olin Lathrop Jun 23 '11 at 18:32
@Olin Is there any way to get the dsPIC or MPLAB C30 to save a call stack? I'm getting a "<call trace not available due to optimisation>" error when I try viewing the call trace. – Thomas O Jun 23 '11 at 22:35
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