Re: [Simulavr-devel] [PATCH] use static callbacks instead of template param for IOReg

[panic]

panic:
> Hi,
> 
> Michael Hennebry:
>> The PINx toggle of PORTx bits is not a new feature.
>> simulavr must support this.
>> A RMW implementation of SBI also does not work on registers with interrupt 
>> flags.
> 
> At least according to avrlibc doc, this is not recommended for interrupt
> flags:
> 
> http://www.nongnu.org/avr-libc/user-manual/FAQ.html#faq_intbits
> http://www.atmel.com/webdoc/avrlibcreferencemanual/FAQ_1faq_intbits.html

The actual motivation might be that some interrupt flag registers are
also located above 0x20 and cannot be used together with SBI. Thusly,
"|=" would be evaluated to in/eor/out possibly clearing too many flags.
A programmer would have to look up whether the register with the flag to
clear is above or below 0x20 and then use = or |=. Hence, the
recommendation to never use |= to clear interrupt flags.
For registers below 0x20, |= via SBI instruction should work though.

On the other hand, the PINx registers are always located below 0x20.

Cheers,
panic