Re: [avr-libc-dev] Can pgmspace.h __LPM_xxx__ macros become inline fn's?

[E. Weddington]

Theodore A. Roth wrote:

> On Thu, 30 Sep 2004, Bill Somerville wrote:
>
>  
>
> > Is there any reason why the LPM macros in avr/pgmspace.h cannot be
> > reimplemented as inline functions?
> >
> > E.g.:
> >
> > __inline__
> > uint8_t
> > __LPM_classic__( uint16_t addr )
> > {
> >   uint8_t result;
> >   __asm__
> >           (
> >                  "lpm" "\n\t"
> >                  "mov %0, r0" "\n\t"
> >                  : "=r" (result)
> >                  : "z" (addr)
> >                  : "r0"
> >                  );
> >   return result;
> > }
> >
> > This avoids warnings in C with -pedantic compiler switch, makes the code
> > leagal in C++ (it is an error with -pedantic switch in C++).
> >    
>
> Those seem like pretty good reasons for switching to inline functions to
> me.
>
> If no one comes up with a strong reason against this, I have no
> major objections.
>
> My only (very weak) objection is that I've found that gdb can not step
> over an inlined function. That makes debugging a bit of a pain some
> times.
>
> Although, other advantages are type checking and the ability to step
> through an inline function in the debugger when you need to see what it
> is doing.
>
> One nit: should the function definition be "static __inline__ ..."
> instead of just "__inline__ ..."?
>  

Hmm.
All of the pgm_* API is implemented as #defines that eventually boil 
down to the __*LPM* style identifiers. Wouldn't declaring them as static 
make them non-visible outside of avr/pgmspace.h? I don't think this is 
desirable.

I'd also be careful about making this into inline functions, as GCC 
*sometimes* inlines them, and sometimes doesn't. And you might very well 
find the pgm_read* routines in bootloaders where you do *not* want to 
have subroutines called. I would investigate using __attribute__ 
((always_inline)) on the functions. See the discussion of this attribute 
in the GCC manual here:
<http://gcc.gnu.org/onlinedocs/gcc-3.4.2/gcc/Function-Attributes.html#Function-Attributes>
If the always_inline attribute is used, then it preserves the same 
functionality as what happens with the preprocessor macro.

However, I don't know if using function attributes will still invoke the 
-pedantic problem.

Eric