UART RX interrupt triggered even though nothing on RX line

Jim Granville wrote:
> galapogos wrote:
> > Meindert Sprang wrote:
> >
> >>"galapogos" <goister@gmail.com> wrote in message
> >>news:1166003074.092524.280660@16g2000cwy.googlegroups.com...
> >>
> >>>So you think it's an issue with disconnection rather than reconnection.
> >>>I was kinda suspecting the latter.
> >>
> >>It can be both.
> >>Both actions can produce transients on the data and handshake lines, so the
> >>only way to deal with this is when you detect a connection again, clear all
> >>data and status regs and flags and only then enable the ints again. And even
> >>then your protocol  should be able to handle spurious data in the initial
> >>bytes. It is a bit like hitting your return key once or twice when you have
> >>connected to a modem, in order to see the "OK" message before sending real
> >>commands.
> >>
> >>Meindert
> >
> >
> > I found out that those 2 extra interrupts actually also trigger one of
> > the 3 error status bits that I thought I was checking but actually
> > negated for debugging purposes earlier. They are the buffer overrun,
> > parity and framing error bits. Now I'm actually doing the checking and
> > handling the errors, i.e. not copying them into my FIFO so that sorta
> > handles it. Still not sure why I'm even getting those 2 interrupts
> > though but at least they're taken care of. I tried clearing those
> > status bits on disconnect and also on reconnect, but they still appear.
> > I guess it's a good thing since otherwise, it might get pushed into the
> > FIFO.
>
>  From your comments on the 20ms pin-polling (DSR?) scheme, it sounds like
> there is potential there to slice RX data.
> If you are sure there are enough margins so that RX activity change
> occur (well) after the polling has seen the handshake line, then that
> suggests a chip artifact.
> Even when disabled, is there _any_ RXD activity ?
> I've seen uarts before that did not cross the baud-configure boundary
> very well.

I'm not sure what DSR is. Anyway, I toggle a pin whenever my RX isr is
called, and then monitor various lines(including RX/TX lines) on the
logic analyzer triggered by that pin. I don't see any activity on the
RX/TX pins at all when the isr is called, except when I do my error
handling code.