Sorry,
i meant first
volatile unsigned char TimerTick;
and then
TimerTick = 10;
Since you need the variable in the ISR routine.
Ruud.
On Tuesday 15 April 2008 20:12, Karl O. Feger wrote:
> Dear all,
>
> I'm relatively new to AVR-GCC and try to do something,
>
> that is standing procedure in C51 for me. I want to
>
> program a delay based on a timer-ISR. The code looks
>
> like this:
>
> *********************************
>
> //isr-test, very basic
>
> // cpu: ATMega128
>
> // speed: 16 mhz
>
>
>
>
>
> #include <avr/io.h>
>
> #include <avr/interrupt.h>
>
>
>
>
>
> unsigned char TimerTick;
>
>
>
>
>
> //---------------------------------------
>
> // Timer/Counter1 Compare Match A
>
> //---------------------------------------
>
>
>
> ISR(TIMER1_COMPA_vect) // timer_compare_a
>
> {
>
>
>
> TimerTick ? TimerTick-- : 0;
>
> }
>
>
>
> //---------------------------------------
>
> // main
>
> //---------------------------------------
>
>
>
> int main()
>
> {
>
>
>
>
>
> unsigned char a;
>
>
>
> // --- TIMER1_COMPA irq ---
>
> // selected time = 10 ms (160000 ticks)
>
> // prescaler = 8 (8 ticks ... 32.768 ms)
>
> TCCR1B = (1<<WGM12)|(1<<CS11);
>
> OCR1AH = 0x4e;
>
> OCR1AL = 0x20;
>
> TIMSK |= (1<<OCIE1A);
>
>
>
> // main loop
>
> sei();
>
>
>
> for (;;)
>
> {
>
> TimerTick = 10;
>
> while(TimerTick);
>
> a = ~a;
>
> }
>
> return(0);
>
> }
>
> ********************************
>
>
>
> When I compile this without optimization (-O0)
>
> Everything is just fine and as expected. When I select
>
> ANY other optimization level, the resulting assembler
>
> code looks like this (starting at "TimerTick = 10;"):
>
> **********************
>
> 45: TimerTick = 10;
>
> +00000086: E08A LDI R24,0x0A Load
>
> immediate
>
> +00000087: 93800100 STS 0x0100,R24
>
> Store direct to data space
>
> +00000089: CFFF RJMP PC-0x0000
>
> Relative jump
>
> ***********************
>
> so the program stops here and loops.
>
>
>
> Where is my thinking wrong? I tried all sources I could
>
> imaging.
>
>
>
> Thanks for any help
>
> Karl
>
>
>
>
>
>
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