> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]
> On Behalf Of Ruud Vlaming
> Sent: Friday, October 03, 2008 10:28 AM
> To: avr-chat@nongnu.org
> Subject: [avr-chat] Is this efficient?
>
> To find out if a register is in the io space in .c files,
> i use the following, ugly, construct:
>
> #undef _SFR_IO8
> #define _SFR_IO8(arg) (arg)
> #if (TIMSK < 0x40)
> blah blah
> #else
> bloh bloh
> #endif
> #undef _SFR_IO8
> #define _SFR_IO8(arg) (*(volatile uint8_t *)((arg) + 0x20))
>
> I cannot test it with _SFR_IO_REG_P, although that macro seems to be
> meant for the purpose:
>
> #if _SFR_IO_REG_P(TIMSK)
>
> for that gives the error:
> error: operator '*' has no left operand
>
> Somewhere i am missing the point i guess.
> Who knows the proper way to do such things?
The _SFR_IO_REG_P() macro is designed to be used in the C code itself, not in
any preprocessor statements. Something like:
if _SFR_IO_REG_P(TIMSK)
{
// TIMSK is an IO register.
}
else
{
// TIMSK is not an IO register.
}
Thoroughly untested. And yes it creates more code, as it does not conditional
compilation.
If you look at the implementation of the _SFR_IO_REG_P() macro, it is taking
the address of the register and typecasting. IIRC, the preprocessor is not that
smart. It is not enough C-aware to be able to handle this in preprocessor
statements. But it should work in regular C code.
HTH
Eric
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