Lpc2000

I haven't had any problems at all with the direct write.
The weirdest things were happening though with the masking.
For example, comm_tx[tx_head++]=ch; would cause problems
too (protected but only with U0IER=0x01 ),
whereas :
temp = (tx_head+1)%RS232_SIZE;
...
comm_tx[tx_head]=(UCHAR)c;
tx_head=temp;

wouldn't .....
Go figure....
I need to retest all these permutations.

-- Kris





----- Original Message -----
From: "J.C. Wren" <jcwren@...>
To: <lpc2000@yahoogroups.com>
Sent: Monday, February 23, 2004 3:18 AM
Subject: Re: [lpc2000] UART TX FIFO and INTs problem - SOLVED


> Bill Knight wrote:
>
> > Kris
> >   Thanks for spotting this.  It's the old spurious interrupt problem.
> > The fix is to disable global interrupts around the first
read-modify-write
> > instruction.  Doing the direct write (U0IER = xxx) can still allow the
> > problem
> > to happen.  What happens is the interrupt occurs and is recognized while
> > the masking instruction is executing but before it has completed.  Then
> > when the instruction does complete, the interrupt can't find the vector
> > so uses the default.  So to fix:
> >
> [snip]
>
>     Why should the direct write cause this problem?  The issue with
> read-modify-write makes perfect sense, but the write should be an atomic
> operation.  How would you get an interrupt between <nothing> and the
write?
>
>     --jc
>
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