Re: [avr-gcc-list] About context saving in Vectors

[Dave Hylands]

Hi Lin (and Dennis),

>> And the function ISR(USART1_RX_vect) in Linux saves even fewer registers.
>
>  The solution is to NOT call functions from within your ISR.  That is just
> evil.  Get your data in the ISR, put it in a mailbox or buffer and have a
> regularly scheduled function handle the details from outside the ISR.  I
> like to use ring buffers to store data from an ISR.  When using the ring
> buffer the ISR modifies the "write" pointer, not the read pointer and the
> processing function outside the ISR modifies the read pointer and not the
> write pointer.  This means that those pointers don't need "push/popped" in
> the ISR either.

And here's some code that implements such a ring buffer. As David
Kelly points out, as long as the index type is uint8_t, then nothing
special is required (which for this particular implementation means
that buffers upto 128 entries would be supported)

<http://websvn.hylands.org/filedetails.php?repname=Projects&path=%2Fcommon%2FCBUF.h&rev=0&sc=0>

It's important that the queue be declared volatile (as myQ is in the sample).

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.DaveHylands.com/