Re: [avr-libc-dev] Optimization safe access to the timers

[Galen Seitz]

Enoch H. Wexler <address@hidden> wrote:

> Hi Paulo,
> 
> 
> Strange, the problem does not show in my simplified test... but here's
> some real code excerpt and its disassembly (compiled with -Os using
> avr-gcc 4.1.0):
> 
> (1) Using TCNT3 directly:
> 
> when = TCNT3 + (7200 / 9 * 10 - 1); /* > 1 sec delay */
> while (when - TCNT3 >= 0)
>     UDR1;
> 
> 000013ce <kuku>:
>     13ce:    80 91 88 00     lds    r24, 0x0088
>     13d2:    90 91 89 00     lds    r25, 0x0089
>     13d6:    80 91 88 00     lds    r24, 0x0088
>     13da:    90 91 89 00     lds    r25, 0x0089
>     13de:    83 b1           in    r24, 0x03    ; 3
>     13e0:    fa cf           rjmp    .-12         ; 0x13d6 <kuku+0x8>
> 


The type of TCNT3 is unsigned, so the expression (when - TCNT3 >= 0)
is always true due to C type conversion rules.  You should cast
TCNT3 to int16_t.

galen