cycling through leds - c

Question

Please help me with this code, it is making me crazy. This is a very simple program with 8-bit timer, cycling through all 8 leds (one-by-one). Am using ATSTK600 board.
My timers are working well, I think there is some problem with the loops (when I debug this program using avr studio-gcc, I can see all the leds working as I want but when I transfer it on board...leds don't blink). Am going crazy with this type of behavior.
Here is my code:
#include <avr/io.h>
#include <avr/interrupt.h>
volatile unsigned int intrs, i, j = 0;
void enable_ports(void);
void delay(void);
extern void __vector_23 (void) __attribute__ ((interrupt));
void enable_ports()
{
DDRB = 0xff;
TCCR0B = 0x03;
TIMSK0 = 0x01;
//TIFR0 = 0x01;
TCNT0 = 0x00;
//OCR0A = 61;
intrs = 0;
}
void __vector_23 (void)
{
for(i = 0; i<=8; i++)
{
while(1)
{
intrs++;
if(intrs >= 61)
{
PORTB = (0xff<<i);
intrs = 0;
break;
}
}
}
PORTB = 0xff;
}
int main(void)
{
enable_ports();
sei();
while(1)
{
}
}

Answer 1

Your interrupt routine is flawed. intrs counts only the number of times the loop has executed, not the number of timer interrupts as its name suggests. 61 iterations of that loop will take very little time. You will see nothing perceivable without an oscilloscope.
The following may be closer to what you need:
void __vector_23 (void)
{
intrs++;
if(intrs > 60)
{
intrs = 0;
PORTB = (0xff<<i);
i++ ;
if(i == 8 )
{
i = 0 ;
PORTB = 0xff;
}
}
}
Although setting the compare register OCR0A to 61 as in your commented out code would avoid the need for the interrupt counter and reduce unnecessary software overhead.

Answer 2

Are you sure that the code downloaded to the board is not optimized?
Have you attached volatile attribute to the PORTB identifier?
Is there a way for you to slow down the code (outside the debugger)? Any chance it's running but fast that you don't see it?
Can you verify that your intended code is in fact running (outside the debugger)?

Answer 3

When interrupt occurs, handler very quickly counts 62*9 times and finally sets PORTB to 0x00, so leds do only very short flash which is not visible. You see it in sumulator just because it runs slower and do not emulate visual dimming effect of fast port switching. Program has a design flaw: it tries to do full blinking cycle in single interrupt. That's wrong--only a single step should be performed in interrupt call. So handler should look like this:
void __vector_23 (void)
{
intrs++;
if(intrs >= 61)
{
PORTB = (0xff<<i);
intrs = 0;
i++;
if(i>8) i = 0;
}
}
Try this.
There is guidelin on interrupts handlers: Interrupt handler should be as fast and short as possible. Do not perform complex tasks in interrupts (cycle loop is one of them, if you get cycle in interrupt, try to remove it). Do not wait or delay in interrupts.

Answer 4

If you're seeing the behaviour you want when debugging with avr studio-gcc, then that gives you some confidence that your program is "good" (for some sense of the word "good"). So it sounds as though you need to focus on a different area: what is the difference between your debug environment and your stand-alone download?
When doing a stand-alone download, do you know if your program is running at all?
Are the LEDs blinking, or turning on at all? You don't explicitly say in your question, but that question could be very relevant to the debugging process. Does it look like the right behaviour, running at a different speed? If so, then your program is probably not doing some sort of initialisation that the debugger was doing.
When doing a stand-alone download, is the program being compiled with different settings compared to the debug version? Perhaps compiler optimisation settings are changing your program's timing characteristics.
(Your question would be better if you gave more detail about what the stand-alone download is doing. In general, it is hard for someone to debug a remote system when they're given few or no details about what is happening. Do all/some of the LEDs turn on at all?)