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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