On Mon, Jul 21, 2014 at 09:47:05PM +1200, IVP wrote:
> Sorry, I don't do C myself so can't answer that. I'd be surprised
> if it did because it adds instruction cycles to an ISR that may be
> or definitely are not needed. That is, some ISRs are required to
> be as short and/or reactive as possible

Saving registers is usually done by compilers.  The exact
implementation will vary.  Usually everything that might change is
saved, and yes, this does indeed slow the code.

Saving registers only if they are used is an optimisation some
compilers may do.  I don't know if any of the compilers mentioned in
this thread do it.  Can easily check by reading the generated
instructions.

Therefore switching to assembly and making these decisions yourself may
save cycles at the expense of more code care.

On Mon, Jul 21, 2014 at 04:59:24AM -0500, Richard R. Pope wrote:
> Jan-Erik has confirmed that the compiler does save the context info
> automatically.

p.s. this seems redundant; Joe is on the list and should have received
Jan-Erik's post.  ;-)  Remember that posts may arrive out of order for
any of us.

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James Cameron
http://quozl.linux.org.au/
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