AVR-Chat

Thanks David, that's helpful.

All the best,

Cat

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From: "David Kelly" <dkelly@hiwaay.net>
Sent: Sunday, June 08, 2008 6:36 PM
To: <AVR-Chat@yahoogroups.com>
Subject: Re: [AVR-Chat] AvrStudio4 (2008), WinAVR (2007-05...) and Dragon 
problem debugging C code (jtag)

>
> On Jun 8, 2008, at 7:00 PM, Cat Hotmail wrote:
>
>> I'm not sure of all that "volatile" does (I know I need it for
>> variables
>> that I use both in interrupts and out).
>
>
> Volatile informs the compiler that the object may change between the
> compiler's uses. Therefore the compiler has to read it immediately
> before use if its value is needed. That it can't trust a copy of the
> variable laying around in a register. And when changing the value it
> must write it out immediately. And not merge the access across
> multiple statements.
>
> If you say:
>
> volatile uint8_t v;
>
> v = 1;
> v = 0;
> v = 1;
>
> the compiler is not allowed to notice the end result is v = 1 and skip
> the v = 0 step. With full optimization it just might skip those other
> steps. Thats why I asked if it was performing the skipped lines that
> you could not single-step debug.