Re: [avr-libc-dev] Determine defined port

[Harald Kipp]

Eric,

thanks for your response, but still I'm not able to use it during
preprocessing to exclude or include specific code.

In the meantime I found out, that not even my proposed solution
worked. :-( It's a lot more complicated than expected. The related
document is here
http://gcc.gnu.org/onlinedocs/gcc-3.3.3/cpp/Argument-Prescan.html#Argument%20Prescan

I finally discovered a solution by using two macros as described in that
document _and_ use them before including any avr-libc headers like
avr/iom128.h.

Now I'm in doubt, if all that had been worth the hassle and how
portable my code will be. Well, at least I got some deeper
insight into the preprocessor.

Harald



At 09:17 23.08.2004 -0600, E. Weddington wrote:
> Harald Kipp wrote:
>
> > Hi all,
> >
> > I stumbled over the following pre-processor problem.
> >
> > Somewhere in an include file there's a macro
> >
> >   #define MY_PORT  PORTC
> >
> > User's should be able to adapt the program to their hardware
> > be simply changing this include file.
> >
> > To make the code independent from the specified port,
> > I need something like
> >
> >   #if (MY_PORT == PORTC)
> >   /* Do something PORTC specific, like disabling XMEM */
> >   #endif
> >   sbi(MY_PORT, 7);
> >
> > Obviously this won't work, because PORTC is an already dereferenced
> > volatile pointer. No chance to retrieve the pointer address, right?
> Actually you *can* retrieve the pointer address. The register names can be 
> used as variables, so you can take the address of it like so:
>
> &PORTC
>
> HTH
> Eric