Just a guess...

If you misspell the name of the interrupt handler on the #pragma interrupt=
=20
statement the compiler wouldn't know to end the routine with a RETFIE=20
instead of a RETURN.

-- Bob Ammerman
RAm Systems

----- Original Message -----=20
From: "Joe Wronski" <jwronski@stillwatereng.net>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Wednesday, May 09, 2012 10:54 AM
Subject: Re: [PIC]Interrupts with 18F4550 and C18


> Without actually digging into the doc for the 18F part in the example
> (18C452 ?), I can give some answers:
> o Unconditional goto is due to limited program space in the interrupt
> vector area.
> o Retfie is generated by the compiler, probably due to the #pragma
> interrupt directive.  Look at View->Disassembly Listing after building.
> o Can't speak to the GIE issue without further digging, but if it is
> disabled by the interrupt mechanism, your cods should re-enable it,
> unless it is implicitly done by the retfie.
>
> There should be no differences in the chip operation whether using C or
> assembler.  Always look to the assembler produced by the compiler.
>
> Here is the interrupt exit code produced by C18 including the "missing"
> retfie:
>
>   00F2    52E5     MOVF 0xfe5, F, ACCESS
>   00F4    CFE5     MOVFF 0xfe5, 0xfda
>   00F6    FFDA     NOP
>   00F8    0011     RETFIE 0x1
>
> Joe W
>
>
>
> On 5/9/2012 3:30 AM, Manu Abraham wrote:
>> Hi,
>>
>> The C18 example states that an interrupt handler is to be defined thus:
>> (in MCC18\examples\Interrupt\main.c)
>> //----------------------------------------------------------------------=
------
>> // High priority interrupt vector
>>
>> #pragma code InterruptVectorHigh =3D 0x08
>> void
>> InterruptVectorHigh (void)
>> {
>>    _asm
>>      goto InterruptHandlerHigh //jump to interrupt routine
>>    _endasm
>> }
>>
>> //----------------------------------------------------------------------=
------
>> // High priority interrupt routine
>>
>> #pragma code
>> #pragma interrupt InterruptHandlerHigh
>>
>> void
>> InterruptHandlerHigh ()
>> {
>>    if (INTCONbits.TMR0IF)
>>      {                                   //check for TMR0 overflow
>>        INTCONbits.TMR0IF =3D 0;            //clear interrupt flag
>>        Flags.Bit.Timeout =3D 1;            //indicate timeout
>>        LATBbits.LATB0 =3D !LATBbits.LATB0; //toggle LED on RB0
>>      }
>> }
>>
>>
>> But I can't seem to figure out why that INTCONbits.GIEH is disabled
>> after once it has run through the handler. In asm, the Global Interrupt
>> handler is enabled after a retfie, but with C18 and the 18F4550, this
>> doesn't seem to be the case, I do need a retfie as follows, for the
>> interrupt to be re enabled. Any idea why it is thus ?
>>
>> Additionally, I have this question, the ISR is unconditionally jumping t=
o
>> another function. Especially in an ISR, I can't really reason why that
>> would be a good practice ?  (Although I can assume that the functions
>> would expand to labels in asm. But still doesn't explain the missing=20
>> retfie)
>>
>>
>>
>> void low_isr(void)
>> {
>>      if ((PIE1bits.TMR2IE =3D=3D 1)&&  (PIR1bits.TMR2IF =3D=3D 1)) {
>>          PIR1bits.TMR2IF =3D 0;
>>                 DisplayDigit(segment, display[segment]);
>>      }
>>      _asm
>>          retfie 0
>>      _endasm
>> }
>>
>> #pragma code low_vector =3D 0x18
>> void low_vector (void)
>> {
>>      _asm goto low_isr _endasm
>> }
>>
>> void init_timer2(void)
>> {
>>      OpenTimer2(TIMER_INT_ON&  T2_PS_1_4&  T2_POST_1_1);
>>       PR2 =3D 223;
>>      RCONbits.IPEN    =3D 1; /* Interrupt priority enable */
>>          IPR1bits.TMR2IP    =3D 0; /* TMR2 Low priority */
>>       INTCONbits.GIEL =3D 1;
>>         INTCONbits.GIEH =3D 1;
>> }
>>
>> void main()
>> {
>>      TRISD =3D 0;
>>      TRISC =3D 0;
>>      init_timer2();
>>
>>      while (1) {
>>
>>          }
>> }
>>
>> Thanks,
>> Manu
>
> --=20
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