At 12.17 2011.10.26, you wrote:
>Em 26/10/2011 06:47, William "Chops" Westfield escreveu:
>> On Oct 25, 2011, at 4:23 AM, Electron wrote:
>>
>>>>    digitalWriteFast(3,1);  // compiles to LATxSET =3D b
>>>> 9d00135c:       24020001        li      v0,1
>>>> 9d001360:       3c03bf88        lui     v1,0xbf88
>>>> 9d001364:       ac6260e8        sw      v0,24808(v1)
>>>> that was digitalWriteFast, I have seen more horrific output from =20
>>>> the compiler.
>> That does look pretty optimal for setting an output pin; I'm happy =20
>> (aside from the lack of optimization when manipulating other pins =20
>> "nearby" in the code.)  (digitalWriteFast() is a macro to implement =20
>> the digitalWrite() "standard Arduino function" when all the arguments =20
>> are constants.  A horrible kludge depending on gcc features and =20
>> compile-time optimization.  But about 20x faster than the function.
>>
>> BillW
>>
>
>
>I agree.
>
>What the OP wants?

The incriminated code was:

     digitalWriteFast(3,1);  // compiles to LATxSET =3D b
9d00135c:       24020001        li      v0,1
9d001360:       3c03bf88        lui     v1,0xbf88
9d001364:       ac6260e8        sw      v0,24808(v1)
     digitalWriteFast(3,0);  // compiles to LATxCLR =3D b
9d001368:       3c03bf88        lui     v1,0xbf88
9d00136c:       ac6260e4        sw      v0,24804(v1

asm instruction #4 is redundant (IMHO even the #2, as a register should
be devoted to store the SFR base at ~all times, as we're talking about
a MPU here, not WindowsNT code in ring3).


>I can see "load the bit mask" -> "load base address" -> "output the
>value at base address+offset".
>How could it be optimized further? Only if he preloads everything, but
>then he would have two wasted registers.
>
>
>Isaac
>
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