Re: [avr-gcc-list] generic queue library for AVR GCC?

[Bruce D. Lightner]

Bjarne Laursen wrote:

> Bruce D. Lightner wrote:
> > How about this...
> >
> >     #include <avr/io.h>
> >     #include <avr/interrupt.h>
> >     #include <inttypes.h>
> >     #define begin_critical_section()  SREG; cli()
> >     #define end_critical_section(val) SREG = val
> >     ....
> >     {
> >         unsigned char sreg = begin_critical_section();
> >         sm_qin = sm_qout = 0;   // reset queue pointers
> >         end_critical_section(sreg);
> >     }
> >
> > This gets you the same, optimally efficient AVR code.
>
> but be careful
> this will not work:
>
>        unsigned char cr;
>        if (bSomeFlag) cr = begin_critical_section();
>        sm_qin = sm_qout = 0;   // reset queue pointers
>        if (bSomeFlag) end_critical_section(cr);
>
> cli() will get executed even if bSomeFlag is 0.
> maybe an inline function will do the job.

OK.  Let's continue to "beat this dead horse" to make sure it's
*really* dead! :-)

You all of course know that "," can be used in place of ";" to
separate C statements.  Therefore we can make a minor change to
the first macro definition...

     #include <avr/io.h>
     #include <avr/interrupt.h>
     #include <inttypes.h>
     #define begin_critical_section()  SREG, cli()
     #define end_critical_section(val) SREG = val
     ....
     {
         unsigned char sreg = begin_critical_section();
         sm_qin = sm_qout = 0;   // reset queue pointers
         end_critical_section(sreg);
     }

Note the "," just before the "cli()".

This makes Bjarne's...

  if (bSomeFlag) cr = begin_critical_section();

...work just fine.

Best regards,

Bruce

--
 Bruce D. Lightner
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