larwe@larwe.com (Lewin A.R.W. Edwards) wrote in
news:608b6569.0407121839.23bc5397@posting.google.com: 

>> > But does anyone have any idea about what was going on with not
>> > being able to reset it? I tested it out today after the AVR had
>> > been unpowered for 
>> 
>> Here's just a guess.  You may have a sneak path
>> for power back to your board.  Unplug *all* cables,
>> wait a minute, and see if it's reset.
> 
> This is a known issue with the STK500. If you have it plugged into a
> PC that provides a ground return, the power switch is inoperative -
> both positions are "on".

I don't have an STK500 - I'm just using a simple 5V power supply and a AVR 
ISP. I guess maybe it was getting power through the avr isp? It was still 
connected to the computer...

-Michael

In article <40f2fcc6.14228970@News.individual.net>, iddw@hotmail.com 
says...
> On Mon, 12 Jul 2004 20:00:05 GMT, R Adsett
> <radsett@junk.aeolusdevelopment.cm> wrote:
> 
> >In article <Xns95247EC688106nleahcim@204.127.199.17>, 
> >nleahcimathotmaildotcom@nowhere.com says...
> [...]
> >> Instead of using RETI - could I simply set the global interrupt flag by 
> >> executting SEI? Or is there more to it than that? Thanks,
> [...]
> >You need to restore the entire processor status not just the interrupt 
> >enable bit(s) to what it was before the interrupt occurred.  That's why 
> >there is a separate unique instruction for returning from an interrupt as 
> >opposed to returning from a subroutine.  If you don't use it then 
> >generally "Bad Things Happen".
> 
> Well, the subject _is_ the AVR.  From Atmel's instruction set manual:
> 
>     RETI - Return from Interrupt
>     [...]
>     Returns from interrupt.  The return address is loaded from the
>     STACK and the global interrupt flag is set.
>     Note that the status register is not automatically stored when
>     entering the interrupt routine.  This must be handled by the
>     application program.  The stack pointer uses a pre-increment
<snip>
> That's it.  No more.  The processor status is not saved on entry into
> the ISR, and RETI does not "restore" any such state, other than
> setting the I bit in SREG.
Figures, it would be one of the architectures that don't fit in the 
'generally'.  I'd still want to use the reti for symmetry, documentation 
and parsimony but it appears the evil of avoiding it doesn't run very 
deep.

Robert

> > But does anyone have any idea about what was going on with not being able 
> > to reset it? I tested it out today after the AVR had been unpowered for 
> 
> Here's just a guess.  You may have a sneak path
> for power back to your board.  Unplug *all* cables,
> wait a minute, and see if it's reset.

This is a known issue with the STK500. If you have it plugged into a
PC that provides a ground return, the power switch is inoperative -
both positions are "on".

On Mon, 12 Jul 2004 20:00:05 GMT, R Adsett
<radsett@junk.aeolusdevelopment.cm> wrote:

>In article <Xns95247EC688106nleahcim@204.127.199.17>, 
>nleahcimathotmaildotcom@nowhere.com says...
[...]
>> Instead of using RETI - could I simply set the global interrupt flag by 
>> executting SEI? Or is there more to it than that? Thanks,
[...]
>You need to restore the entire processor status not just the interrupt 
>enable bit(s) to what it was before the interrupt occurred.  That's why 
>there is a separate unique instruction for returning from an interrupt as 
>opposed to returning from a subroutine.  If you don't use it then 
>generally "Bad Things Happen".

Well, the subject _is_ the AVR.  From Atmel's instruction set manual:

    RETI - Return from Interrupt
    [...]
    Returns from interrupt.  The return address is loaded from the
    STACK and the global interrupt flag is set.
    Note that the status register is not automatically stored when
    entering the interrupt routine.  This must be handled by the
    application program.  The stack pointer uses a pre-increment
    scheme during the RETI.

    [...]

    Operation:
    PC(15:0) <- STACK     Devices with 16 bits PC[...]

    [...]

    Status Register (SREG) and Boolean Formula

    [...I bit set, other bits unaffected...]

That's it.  No more.  The processor status is not saved on entry into
the ISR, and RETI does not "restore" any such state, other than
setting the I bit in SREG.

So SEI should take care of you.  You should clear the stack every now
and again to ensure it doesn't overflow, but I'm not sure that would
affect your example code anyway...

Regards,

                               -=Dave
-- 
Change is inevitable, progress is not.

Michael wrote:

> But does anyone have any idea about what was going on with not being able 
> to reset it? I tested it out today after the AVR had been unpowered for 
> about 12 hours - and it did the same exact thing. I just don't understand. 
> Perhaps does it remember all the states of the registers when it turns on 
> or something?

Here's just a guess.  You may have a sneak path
for power back to your board.  Unplug *all* cables,
wait a minute, and see if it's reset.

R Adsett <radsett@junk.aeolusdevelopment.cm> wrote in
news:95CIc.160914$rCA1.108583@news01.bloor.is.net.cable.rogers.com: 

> In article <Xns95247EC688106nleahcim@204.127.199.17>, 
> nleahcimathotmaildotcom@nowhere.com says...
>> "tanya" <tanya.anne@bigpond.com> wrote in
>> news:ccsoog$pks$1@newshost.mot.com: 
>> 
>> > Interrupts are automatically disabled on entry to INTER0 Interrupt
>> > Service Routine.
>> > Since you are not enabling interrupts in the INTER0 loop, no
>> > further interrupts will be serviced.
>> > If you used the RETI instruction,  flags (including interrupt
>> > status) and PC would be restored.
>> > A suggested approach would be to have a main loop that executes
>> > with interrupts enabled, with Interrupt Service Routines returning
>> > to this loop via RETI instructions.
>> > 
>> > Tanya
>> 
>> Instead of using RETI - could I simply set the global interrupt flag
>> by executting SEI? Or is there more to it than that? Thanks,
>> 
>> Michael
> 
> You need to restore the entire processor status not just the interrupt
> enable bit(s) to what it was before the interrupt occurred.  That's
> why there is a separate unique instruction for returning from an
> interrupt as opposed to returning from a subroutine.  If you don't use
> it then generally "Bad Things Happen".
> 
> Robert
> 

LOL that's what I expected - but I thought I should check to be sure :)

But does anyone have any idea about what was going on with not being able 
to reset it? I tested it out today after the AVR had been unpowered for 
about 12 hours - and it did the same exact thing. I just don't understand. 
Perhaps does it remember all the states of the registers when it turns on 
or something?

Thanks,

Michael

In article <Xns95247EC688106nleahcim@204.127.199.17>, 
nleahcimathotmaildotcom@nowhere.com says...
> "tanya" <tanya.anne@bigpond.com> wrote in
> news:ccsoog$pks$1@newshost.mot.com: 
> 
> > Interrupts are automatically disabled on entry to INTER0 Interrupt
> > Service Routine.
> > Since you are not enabling interrupts in the INTER0 loop, no further
> > interrupts will be serviced.
> > If you used the RETI instruction,  flags (including interrupt status)
> > and PC would be restored.
> > A suggested approach would be to have a main loop that executes with
> > interrupts enabled, with Interrupt Service Routines returning to this
> > loop via RETI instructions.
> > 
> > Tanya
> 
> Instead of using RETI - could I simply set the global interrupt flag by 
> executting SEI? Or is there more to it than that? Thanks,
> 
> Michael

You need to restore the entire processor status not just the interrupt 
enable bit(s) to what it was before the interrupt occurred.  That's why 
there is a separate unique instruction for returning from an interrupt as 
opposed to returning from a subroutine.  If you don't use it then 
generally "Bad Things Happen".

Robert

"tanya" <tanya.anne@bigpond.com> wrote in
news:ccsoog$pks$1@newshost.mot.com: 

> Interrupts are automatically disabled on entry to INTER0 Interrupt
> Service Routine.
> Since you are not enabling interrupts in the INTER0 loop, no further
> interrupts will be serviced.
> If you used the RETI instruction,  flags (including interrupt status)
> and PC would be restored.
> A suggested approach would be to have a main loop that executes with
> interrupts enabled, with Interrupt Service Routines returning to this
> loop via RETI instructions.
> 
> Tanya

Instead of using RETI - could I simply set the global interrupt flag by 
executting SEI? Or is there more to it than that? Thanks,

Michael

Interrupts are automatically disabled on entry to INTER0 Interrupt Service
Routine.
Since you are not enabling interrupts in the INTER0 loop, no further
interrupts will be serviced.
If you used the RETI instruction,  flags (including interrupt status) and PC
would be restored.
A suggested approach would be to have a main loop that executes with
interrupts enabled, with Interrupt Service Routines returning to this loop
via RETI instructions.

Tanya


"Michael" <nleahcimathotmaildotcom@nowhere.com> wrote in message
news:Xns9522B6FABC699nleahcim@204.127.199.17...
> Hi - I was attempting to get the two external interrupts working on an
> AVR. I have attached the code I wrote. My problem is that it seems it is
> only detecting when INT0 is pressed - but I'm not sure about this. The
> way I wrote it I never use the RETI statement - and I don't know if
> other interrupts can be called when a interrupt handler is running.
>
> But also - another problem - so to try to reset the AVR - I just would
> unplug the power - then plug power back in. But for some odd reason this
> didn't work! This has worked just fine for me before - but for some
> reason after doing this - I would have to write a different piece of
> code to the AVR - then rewrite the program I was working on - for it to
> work again. If I simply rewrote the program I was working on to the AVR
> without first writing in a different program, the LEDs would just remain
> off, and it wouldn't work at all. I simply can't figure out what is
> going on here.
>
> Oh - if it matters - my setup right now is that I have an AT90S8515. I
> am programming it with an Atmel AVR ISP. On Port B I have 8 LEDs
> connected to vcc. On port C I have 8 normally closed buttons connected
> to ground. On port D I have two normally open buttons connected to
> ground and to INT0 and INT1.
>
> Also - to use the external interrupts - I set them as inputs with pull
> up resistors. Now I'm starting to think that might not be necessary - is

> it?
>
> Lastly - is it necessary to include both the .device and the .include
> statements? I feel like I've seen code with just one of them.
>
> Thanks!
>
> -Michael
>
>
>
>
>
>
> In case the attachment doesn't work properly - I'll include the code
> below as well:
>
>
>
> .device AT90S8515
> .include "8515def.inc"
>
> .ORG $000
>
> RJMP RESET
> RJMP INTER0            ;int0
> RJMP INPUTLOOP         ;int1
>
> .ORG $00D
>
> RESET:
> LDI R24, low(RAMEND)   ;stack
> OUT SPL, R24
> LDI R24, high(RAMEND)
> OUT SPH, R24
> CLR R24               ;enable interrupts
> OUT MCUCR, R24
> LDI R24, 0xC0
> OUT GIMSK, R24
> SEI
> CLR R24              ;set inputs and outputs and pull up resistors
> OUT DDRC, R24
> OUT DDRD, R24
> SER R24
> OUT PORTC, R24
> OUT PORTD, R24
> OUT DDRB, R24
>
> INPUTLOOP:
> IN R24, PINC         ;write pinc to portb
> OUT PORTB, R24
> RJMP INPUTLOOP
>
> INTER0:
> LDI R24, 0xAA        ;write 10101010 to portb
> OUT PORTB, R24
> RJMP INTER0
>
>