AVR-Chat

>I suppose only the Rxx that are inside the ISR in the lss
>file need savin'
That is clearly true.  The problem is, however, that you can't guarantee that some future version of the compiler won't use different registers compared to the one you're using now.  Even with the same version of the compiler, if you build your application for a different AVR the registers used might change.  These are clearly "accidents waiting to happen" and you can probably count on them happening at the most inopportune time.

In situations like this I would highly recommend moving the entire ISR to a .S file where you'll have complete control and the assurance of no surprises in the future.

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net