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TIM2 update event INT Generation

Question asked by averill.edward on Jan 16, 2013
Latest reply on Jan 16, 2013 by averill.edward
Ok, I'm trying to get a consistent 100 msec interrupt out of Timer2 to drive an external device in steps (but not using PWM).  According to the manual, I have the regs set  right
: ARR, prescaler, all loaded properly and the URS bit set in CR1 to make sure I only see update events.  I'm upcounting, as well.

Now, in theory I should only get my handler called when there's an overflow.. but what I'm seeing is that the instant I leave my ISR there's another INT pending!  Now, I clear the update event bit on entry to the ISR so I see it go away, yet it comes back instantly.. no 100 msec wait.

I'm sure my timebcase is correct and my oscillator (OC1) is set right, if I disable the update event INT I see the counter count up/reload properly...

Is there anything I should be particularly aware of when setting TIM2 to do this kind of thing?  I'm a bit puzzled at this stage, all pointers/manual pages/etc. appreciated.