Now you have me intrigued... ;-0) It really is very weird what you are
experiencing....
A few (long shot) things to try (I hope I don't offend)
1. _How_ are you certain that it is the USART1_TX ISR that is firing? (As
opposed to anther ISR that calls the same handler. or that it is calling a
handler that you _think_ is the TX ISR?
2. Is it possible that one ISR is 'falling through' to the TX ISR? (ie a
forgotten 'reti'?)
3. Can you put a break point in the TX ISR using JTAGICE and THEN examine
the UART registers (ie. is the TXC1 bit in UCSR1A set?
4. In your startup code try to clear any pending interrupts in ICSR1A
before you enable the global Int Flag. (NB that to CLEAR the Int pending
flags you need to write a 1 not a 0.)
5. As an experiment, can you setup the UART with 'real' values (ie. rather
than just clearing the regs to zeroes) and actually try to TX on it. Then
explicitly disable the TXE and RXE bits? I don't know what that will prove
but it might be interesting to see if you can tx on that uart at all?
(?faulty part) or that somehow the UART is getting confused by a zero
baudrate (for eg.)
6. Try to clear the TXC1 bit in UCSR1A in your ISR and see if the repeated
INTs stop. Yes I know that the flag _should_ be cleared when the TXC IST is
completed but...
7. Try Anther chip :-(
8. Try running the software without any debug (ie jtag etc) - again a long
shot, but something to try to see what happens.
I'm not sure if any of this helps but I have been using the Mega128 for a
couple years know (with both UARTS) and have never seen anything that weird.
Please let use know how you get on.
Cheers (or not ;-))
Ivan Vernot
----- Original Message -----
From: "Dave VanHorn" <dvanhorn@dvanhorn.org>
To: <AVR-Chat@yahoogroups.com>; <AVR-Chat@yahoogroups.com>
Sent: Wednesday, March 02, 2005 9:08 AM
Subject: Re: [AVR-Chat] Prototypitis
>
> At 05:02 PM 3/1/2005, Bruce Parham wrote:
>
>
>
> >John Samperi wrote:
> > >
> > > At 08:34 AM 2/03/2005, you wrote:
> > >
> > > >It almost looks like my vector table is wrong or something, but I've
> > > >counted the entries, and checked it against the one in the data
sheet.
> > >
> > > Checked your table and it looks OK. Just one comment (a silly one)
> > > have checked you M103 comaptibility fuse? It may come enabled by
> > > default, perhaps it makes a difference.
> > >
> > > Regards
> > >
> > > John Samperi
> >
> >IIRC, Atmel does ship the M128 with the M103 fuse set...
>
> Yup, BTDT right off the bat. It's hosed in M128 mode.
>
>
>
>
>
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