[En-Nut-Discussion] Preprocessor and Port Definitions

[Harald Kipp]

Hi all,

Some time ago the avr-libc maintainers changed port
definitions from simple
   #define PORTA 0x1B
to
   #define PORTA _SFR_IO8(0x1B)
in order to support
   PORTA = 0;

IMHO this expression is highly non-portable compared to
   outb(PORTA, 0);
because on some platforms (Intel x86) ports are not
memory mapped. However, to some extend I agree with them,
that port access isn't generally portable. For Nut/OS
I'd like to stick with outb(), which makes emulation
much easier. But that's not the point.

The Configurator offers port configuration. I'd like
to avoid, that the user has to configure both, PORT/PIN
and DDR. Unfortunately there seems to be no good solution
to find the DDR for the PORT/PIN.
   #if RTL_RESET_PORT == PORTA
   #define RTL_RESET_DDR DDRA
doesn't work after including avr/io.h, because it finally
results in
   #if (*(volatile unsigned char *)(PORTA)) == (*(volatile unsigned char 
*)(PORTA))
which can't be evaluated by the preprocessor.

In one of the last changes I did, avr/io.h is included
_after_ evaluation of the port macros. This works, but
forcing this strict header file sequence isn't nice.
Beside that, it is still not possible to use
   #if RTL_RESET_PORT == PORTA
within the code.

I already ran into trouble with the included C files.

(I know, that including C files is bad, but without
the Configurator tool creating Makefiles based
on the configuration, there was no other good solution
to avoid source or Makefiles with 99% duplicate lines or
contaminating the sources with preprocessor conditionals.
It's a pain to keep such files up to date. With the
Configurator it's now easy to split files into hardware
independent and depended modules.)

The alternatives I can think of are

1. Let the configurator define AVRPORTA instead of PORTA
   #if RTL_RESET_AVRPORT == AVRPORTA
   #define RTL_RESET_PORT PORTA
   #define RTL_RESET_DDR DDRA

2. Using our own avr/io.h with the traditional definitions.
This would force programmers to use
   outb(PORT, val);
instead of
   PORT = val;

I vote for version 1. Is there another way I missed?

Harald