AVR-Chat

Maybe the problem isn't volatile, but rather a race condition where the ISR
is modifying something your foreground code is using?

It isn't sufficient to tag something volatile, you also need to prevent the
ISR from corrupting the data during your operation.  Volatile just tells the
compiler to not optimize access to the variable since it may change its
value.

Indeed, volatile may not even be needed if you enclose the entire routine
using the variable in a CLI/SEI to prevent the interrupt handler from
mucking things up.  If the ISR doesn't re-enable interrupts, it can optimize
access as much as it likes, same for foreground code.

Volatile is needed, however, for any *external* event, like I/O port
operation where things happen completely beyond the control of the processor
(or more precisely, outside of the CPU state machine operation).  

Cheers!

-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Cat
Sent: Saturday, November 03, 2007 12:21 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Help: volatile variable versus volatile array for
ISR access

Hi Robert,
I didn't say there's any pointer.
Except maybe that the name of an array is a pointer.
I only use "volatile" to make a variable modifiable from an ISR.
And it works, except for arrays.

Thanks,

Cat