[avr-libc-dev] What about to unify _SFR's macroses?

[Dmitry K.]

Hi.

We have 3 variants of SFR usage:
  1. This is default for C/C++.  Port names are like common variables.
  2. Port names are defined as ordinary numbers, suitable to use with
  IN/OUT instructions.
  3. Port names are defined as ordinary numbers (addresses), suitable
  to use with LDS/STS instruction.

The next is too complex to understand (IMHO, worse):
  . With variant #2 the _SFR_MEM_ADDR() returns correct address only for
  ports higher than SREG.  For smaller ports it returns the port number,
  ie value suitable for IN/OUT.
  . With variant #2 the _SFR_ADDR() works correct for C/C++ source only.
  For ASM it is not defined.
  . There is no method to determine the address of ports (those <= 0x5F)
  in ASM source.

What about to change the _SFR macroses:
  . _SFR_MEM_ADDR() must return address for all ports in all variants.
  . _SFR_ADDR() must be defined in both ASM variants.
  . In addition to cryptic __SFR_OFFSET (used for choice the variant)
  add clean macroses to set compatibility level, like:
      #define _SFR_ASM_COMPAT _SFR_ASM_IOPORT

Note, the _SFR_IO_ADDR() and _SFR_IO_REG_P() work correct in all cases.
With proposed changes the _SFR_MEM_ADDR() and _SFR_ADDR() would be equal.

Also, I prefer to have default for ASM the variant #3: this is compatible
with old programs and corresponds to Atmel's datasheet examples. However,
it too late to change.

Please, opinions.

Thanks,
Dmitry.