AVR-Chat

On 4/20/2012 7:35 PM, Don Kinzer wrote:
> --- In AVR-Chat@yahoogroups.com, R E Purcella<repurcella@...>
> wrote:
>> Use volatile variables in ISR routines or strange things happen.
> That sure sounds like a superstition, somewhat akin to "don't walk
> under ladders or bad things will happen".  Neither statement suggests
> any understanding of an actual causal relationship.
>
> You should know why it is necessary or not necessary in each
> particular case.  I would aver that an ISR that cannot be interrupted
> will work perfectly well without volatile (and if present it can be
> safely cast away) for normal variables located in single port RAM
> with no DMA activity.  If you don't know why that is true then you
> don't yet understand the issue.

Yes, and there are cases where volatile is necessary even though the 
value cannot be read and will not change unexpectedly.

Robert
-- 

  From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time?  37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live....
we currently have stock."