I have quite a large codebase running on a PIC24F (PIC24FJ128GB106) and have a Change Notification IRQ handler managing external inputs from the user. Everything's been working well for quite some time, until I changed some clocking to slow the CPU down to it's FRC oscillator during standby.
The problem I'm finding is that one single CN interrupt source isn't triggering the interrupt correctly anymore (the CNIF flag isn't being set), but is still waking the system up from sleep() mode.
All the other external sources which I'm running through this handler are setting the IFS1 register CNIF bit and then immediately entering the IRQ handler after sleep() and being processed as I'd expect.
The troublesome source is waking the system from sleep() then running the next 10 or so lines of code after sleep(), THEN triggering CNIF and entering the interrupt. When it finally goes through the interrupt, the startup conditions have changed and it's redundant.
Everything else is working as before, which is why I'm at a loss. To my knowledge nothing serious was changed.
CN priority is at 7, I've enabled all CNEN bits for each individual source, I've checked all other sources and they all raise the CNIF flag and the CN interrupt enable bit is set. The actual source I'm monitoring is definitely alternating between 0 and 1 (it's a 12v trigger line) when off/on.
Are there any glaring things I might not have checked here?
It's worth mentioning this one external source also causes MPLABX to breakpoint at an imaginary breakpoint after sleep().
... Sleep(); /* Woken up! */ }
The code breakpoints ON the closing brace. I can't stop this happening on this source, but there seems to be no clear reason why. No breakpoint set up, traps, RCON seems OK etc.
All other sources (there are 3 other CN enabled sources) work correctly...