Re: Something I don't understand (loops and interrupts)

[Jim Jackson]

Not looked too closely, but ...

On Fri, 3 Apr 2020, BERTRAND Joël wrote:

> ISR(TIMER1_COMPA_vect, ISR_BLOCK)
> {
>     uint8_t     i;
> 
>     interrupt_counter = (interrupt_counter + 1) % 25;
> 
>     if (interrupt_counter == 0) // 1 s
>     {
>         gpio_toggle(&i_led[i_work]);
>     }
> 
>     // Switch debug leds off
>     for(i = 0; i < i_max; i++)
>     {
>         if (interrupt_counter == 0) serial_send_byte(i);

This gets called every time the for loop iterates, so will get called i_max 
times, all but the first call will cuase serial_send_byte(i) to loop 
waiting for the transmit buffer to empty. You do NOT want to be calling
serial_send_byte(i) in an ISR anyway. Check for interrupt_counter == 0 in 
the main loop, and make sure it's declared volatile.

>         if (i_led[i].timer > 0)
>         {
>             i_led[i].timer--;
> 
>             if (i_led[i].timer == 0)
>             {
>                 gpio_off(&i_led[i]);
>             }
>         }
>     }
> 
>     return;
> }
> 
>       serial_send_byte is a trivial function:
> 
> void
> serial_send_byte(uint8_t byte)
> {
>     while(!(UCSR0A & (1 << UDRE0)));
>     UDR0 = byte;
>     gpio_on(&i_led[i_comm_tx], 5);
> 
>     return;
> }
> 
>       MCU enters in this interrupt (25 times each second). I have checked
> that gpio_toggle(&i_led[i_work]) generates 1 Hz signal. But I don't
> understand why for(i = 0; i < i_max; i++) doesn't run as expected. I
> obtain on serial line (115200, 8N1):
> 
> 10:23:00: 7
> 10:23:00: 8
> 10:23:00: 9
> 10:23:00: 4
> 10:23:01: 5
> 10:23:01: 6
> 10:23:01: 7
> 10:23:01: 8
> 10:23:01: 9
> 10:23:01: 4
> 10:23:02: 5
> 10:23:02: 6
> 10:23:02: 7
> 10:23:02: 8
> 10:23:02: 9
> 10:23:02: 0
> 10:23:03: 4
> 10:23:03: 5
> 10:23:03: 6
> 10:23:03: 7
> 10:23:03: 8
> 10:23:03: 9
> 10:23:03: 4
> 10:23:04: 5
> 10:23:04: 6
> 10:23:04: 7
> 10:23:04: 8
> 10:23:04: 9
> 10:23:04: 4
> 10:23:05: 5
> 10:23:05: 6
> 10:23:05: 7
> 10:23:05: 8
> 10:23:05: 9
> 
>       Value of i_max: 10. But why i doesn't contains values between 0 and 3 ?
> 
>       Best regards,
> 
>       JB
>