Hello Vincent,
The reason for this behaviour is that SDCC turns polling and then clearing
a bit/sbit into an atomic action (using JBC). This is very useful when the
bit is a semaphore or is set inside an interrupt handler.
Maarten
> Hi.
>
> I'm looking at asm generated for the following loop (8051, a CYCFX2LP
> actually) with sdcc 3.1.0#7066:
>
> __sbit __at 0x98+1 TI;
> void main() {
> while (!TI);
> TI = 0;
> }
>
> I get this:
>
> 00101$:
> jbc _TI,00115$
> sjmp 00101$
> 00115$:
>
> Wouldn't it be more efficient, for such bit polling loop, to use instead:
>
> 00101$:
> jnb _TI,00101$
> clr _TI
>
> The first version polls _TI every 7 cycles.
> The second version polls _TI every 4 cycles.
> If _TI is set on loop entry, the first version exits after 4 cycles while
> the
> second exits after 6 cycles. I believe it's sane to assume this is an
> unlikely
> event, so it shouldn't matter too much.
>
> Regards,
> --
> Vincent Pelletier
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