Re: [avr-gcc-list] Extremly confusing behaviour... (Suspectcompiler?, optimization error?)

[Larry Barello]

It looks like the compiler assumes R18 & R19 are preserved across the call.  
Isn't that
a bug?  Gotta look at the assembly for srf08_read() to see what it does with 
those
registers.

----- Original Message -----
From: "Mike Panetta" <address@hidden>
...
> retval = srf08_read(1, 0, pingdata, 2);
>      1fe: 65 e0       ldi r22, 0x05 ; 5
>      200: c6 2e       mov r12, r22
>      202: d1 2c       mov r13, r1
>      204: cc 0e       add r12, r28
>      206: dd 1e       adc r13, r29
>      208: 02 e0       ldi r16, 0x02 ; 2
>      20a: 10 e0       ldi r17, 0x00 ; 0
>      20c: 20 e0       ldi r18, 0x00 ; 0
>      20e: 30 e0       ldi r19, 0x00 ; 0
>      210: a6 01       movw r20, r12
>      212: 60 e0       ldi r22, 0x00 ; 0
>      214: 81 e0       ldi r24, 0x01 ; 1
>      216: 0e 94 9c 04 call 0x938
> PORTA &= ~(_BV(PA1));
>      21a: d9 98       cbi 0x1b, 1 ; 27
> PORTB = retval;
>      21c: 68 bb       out 0x18, r22 ; 24
> } while (retval != 2);
>      21e: 60 17       cp r22, r16
>      220: 71 07       cpc r23, r17
>      222: 82 07       cpc r24, r18
>      224: 93 07       cpc r25, r19
>      226: 71 f6       brne .-100    ; 0x1c4