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

[Michael Hennebry]

On Sat, 1 Jul 2017, panic wrote:

> Example: PINx toggle feature
>
> DDRB = 0xff;
> PORTB = 0xff;
> PINB |= _BV(PB0); // sbi _SFR_IO_REG(PINB), 0

For such things, I recommend against using C code as an example.
What the compiler should do with such things is not obvious.
In the case of avr-gcc,
what it does depends signifcantly on the optimization level.
The choice of sbi or not affects the final outcome, not just the speed.
'Tain't obvious that such statements should even be allowed.

> Expected behaviour:
>  PB0 toggles from 1 -> 0
> PINB is a bit-accessible IO register. The SBI instruction behaves as if
> 0x01 had been written.
>
> Simulavr behaviour:
>  All bits (PB7..PB0) toggle from 1 -> 0.
> Simulavr emulates SBI as RMW:
> - Read PINB: 0xff (each input stage=1)
> - Modify: 0xff | 0x01 --> 0xff
> - Write: 0xff --> PINB, == "PORTB ^= 0xff"
>
> The PINx toggle feature can also be used to toggle pullups ("independent
> on the value of DDRxn").

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Michael   address@hidden
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