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AVR32 IRQ Handling

Posted by Jeff Henshaw on August 16, 2008
I've upgraded my Atmel UC3A0512 project to FreeRtos V5.0.2. My question regards interrupt handling when the ISR might awaken a different thread due to the ISR placing a message into a queue. The serial ISR example, which does exactly that, looks like this. The 2nd function, TerminalIsr() is the one that's actually called when an IRQ occurs:

static portBASE_TYPE TerminalIsrHandler( void )
char Byte;
unsigned long Status;
unsigned longIrqSource;
portBASE_TYPE Qstatus;
portBASE_TYPE HigherPriorityTaskWoken = pdFALSE;

Code That Does Stuff Goes Here...

/* The return value will be used by portEXIT_SWITCHING_ISR() to know if it
should perform a taskYIELD_FROM_ISR(). Note that the macro explicitly
checks for a 1 in order to do the yield operation. */
return (HigherPriorityTaskWoken ? 1 : 0);

// Terminal interrupt service routine.
// Since we might switch tasks inside here, we have to give it the 'naked'
// attribute rather than 'interrupt' and handle the stack via
// In addition, because FreeRTOS is not supposed to run with nested
// interrupts, put all OS calls in a critical section.

static void TerminalIsr( void )
/* This ISR can cause a context switch, so the first statement must be a
call to the portENTER_SWITCHING_ISR() macro. This must be BEFORE any
variable declarations. */

// Now go do the work

/* Exit the ISR. If a task was woken by either a character being received
or transmitted then a context switch will occur. */

My question is - Can I write a single function that handles ISRs rather than incurring the overhead of a 2nd function call? If so, what would the template be for that function?

Thanks !

RE: AVR32 IRQ Handling

Posted by Jeff Henshaw on August 17, 2008
I've dug a little deeper. The IRQ I need to do extra work is the OS Timer tick ISR which uses portSAVE_CONTEXT_OS_INT() and portRESTORE_CONTEXT_OS_INT() and is structurally different than the serial port example I outlined earlier.

So, let's change my question. I can define configUSE_TICK_HOOK to 1 to force the tick ISR to call out to my code. The question is, how do I in the hook routine post data into a queue - a "normal" queue, not a co-routine queue. I'm not using co-routines.

RE: AVR32 IRQ Handling

Posted by Jeff Henshaw on August 17, 2008
Since I'm about to write another serial port handler, I guess I'd still like my first question answered as well.

Thanks again!

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