Re: [avr-gcc-list] do-while problem

[Peter Bosscha]

Hurrah !

You're number 155413 that has fallen for this one. (or thereabouts)
I still think there should be a FAQ for AVRGCC somewhere because you'd
be amazed at how many times this one comes up on the list.

The trick is:
For variables which are updated in interrupt routines always use the
keyword "volatile".

In your case:
volatile unsigned char ABC;

This forces the compiler to reload the variable everytime it uses it.

Regards
Peter Bosscha

>>> Arne Lynge Madsen <address@hidden> 06/05/02 11:33AM >>>
Hi,

I just realized that there migth be a bug in the generated
assempler...


do
 {
  } while (ABC == 0x01 );

 166: 80 91 60 00    lds r24, 0x0060
 16a: 81 30                cpi r24, 0x01 ; 1
 16c: f1 f3                    breq .-4       ; 0x16a

ABC is updated by an interrupt routine. breq.-4 only jumps back to the
cpi statement, so the updated ABC is not taken into account. Loops
forever!


do
 {
  } while (somefunction() != 0);

 132: 86 d1        rcall .+780     ; 0x440
 134: 88 23        and r24, r24
 136: e9 f7        brne .-6       ; 0x132

somefunction() returns ABC. Here brne.-6 jumps back to rcall. It
works!

I currently use these packages:
binutils-2.11.2
gcc-3.0
avr-libc-20011208

Questions:
Where is this error located? binutils, gcc or avr-libc?
Could it be corrected in later versions, if so which one?
Where to report the error?

Best regards
Arne




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