Re: [avr-chat] Inline assembler warning: asm operand 2 probably doesn't match constraints

[Rick Mann]

On Feb 8, 2011, at 05:45:18, Joerg Wunsch wrote:

> In article <address@hidden> you write:
> 
>>      http://pastebin.com/AwuY28F9
> 
> "Unknown paste ID"
> 
> Can't you just attach it?

As a file, I could have. This seemed easier, but I must've deleted the paste.

        http://pastebin.com/AVSapiFz

>>       uint8_t     inverse = ~inPins;
> 
>>                       : "I" (&mPort), "I" (inverse)
> 
> The "IO port" constraint ("I") certainly cannot work here for
> "inverse".
> 
> I think you need a plain "Register" ("r") constraint, so GCC will
> perform the bit complement for you, and then passes the register
> it used for the complement down to the inline asm statement.

Hrm. I tried "r", but got:

src/AVRPort.o: In function `AVRPort::clear(unsigned char)':
/Users/rmann/Desktop/TreasureBox/trunk/Firmware/src/AVRPort.h:61: undefined 
reference to `r24'

Here's the disassembly of AVRPort.o (you can see the only thing in AVRPort.cpp 
is the test() function at the bottom). It seems to have generated a temporary 
for inverse, and not used it. Why it gets that link error is beyond me.


----------------
src/AVRPort.o:     file format elf32-avr


Disassembly of section .text:

00000000 <_Z4testv>:
        asm volatile (  "in     %0, %1"         "\n\t"
                        "andi   %0, %2"         "\n\t"
                        "out    %1, %0"         "\n\t"
                        : "=&r" (temp)
                        : "I" (&mPort), "r" (inverse)
                        );
   0:   8e ef           ldi     r24, 0xFE   ; 254
   2:   92 b1           in      r25, 0x02   ; 2
   4:   90 70           andi    r25, 0x00   ; 0
   6:   92 b9           out     0x02, r25   ; 2

void
test()
{
    gPortA->clear(1);
}
   8:   08 95           ret
----------------