Re: [avr-gcc-list] Global variables and ISRs ???

[Parthasaradhi Nayani]

Hello Vincent,

To be able to modify/access a variable in interrupt,
declare it as "volatile". Secondly, to test your code,
turn off optimization (s=0) in your make file. There
is a problem in your code also - you are not making
flag=0 after you send back the character. HTH.

Nayani


--- Vincent Trouilliez
<address@hidden> wrote:

> Hi gents,
> 
> 
> After the highly technical thread that just ended
> today, I would like to
> pick your brains on something much lower flying so
> to speak, sorry for
> that ! ;-)
> 
> 
> Problem : on my ATmega32, after several experiments
> (only just started
> using it, learning...), I am suffering a big
> problem. It seems that when
> I declare a variable as global, then modify it
> within an interrupt
> routine, the 'main' function can't see that the
> variable has been
> modified, as if it weren't a global variable...
> hmmm.
> 
> The concrete case at hand, was that I tried to
> implement a buffer for
> incoming data on the UART. The ISR would fill the
> buffer and update the
> buffer pointer accordingly. The program in 'main'
> was checking to see if
> the pointer was non-zero and if yes, would send
> characters back to the
> serial port for me to see/check.
> I proved that all was working fine, interrupts etc,
> but somehow, 'main'
> would always see the buffer pointer as zero (hence
> would never react),
> as if the ISR didn't update it. 
> 
> I simplified the program as much as I could, and the
> problem is still
> there. Could anyone have a look at the code below ??
> 
> It receives characters on the serial port, toggle sa
> LED to prove that
> the ISR did get serviced, and sets flag to try and
> communicate with the
> 'main' function.... which fails. 'main' never sees
> the flag as
> set.... :-/ Any help welcome, because I started
> scratching my head an
> hour ago, and now I don't have many hair left to
> pull !! ;-)
> 
> 
> Regards,
> 
> 
> --
> Vince, extremely annoyed...
> 
> 
> 
> #include <avr/io.h>
> #include <avr/interrupt.h>
> #include <avr/signal.h>
> 
> 
> unsigned char flag, bin;  //global variables
> 
> 
> void ioinit (void){
> 
>       DDRD = 0x20;    //PD5 as output for the LED
>       PORTD = 0x00;   //turn LED off at boot.
>       //set up USART
>       UBRRH = 0x00;
>       UBRRL = 12;             //Baud Rate = 9600
>       UCSRA = 0x02;   //mode asynchrone, fast clock
>       UCSRC = 0X86;   //asynchronous, no parity, one stop
> bit, 8 data bits
>       UCSRB = 0x98;   //transmitter and receiver enabled,
> interrupts on
> receiver
>       flag = 0;       
>       sei();
> }
> 
> SIGNAL (SIG_UART_RECV){
> 
>       bin = UDR; //read incoming character to clear
> interrupt
>       PORTD = ~PORTD; //toggle LED to prove ISR was
> serviced                      
>       flag = 1; //tell 'main' about the event
> }
> 
> 
> int main (void){
> 
>       ioinit ();
>       while(1){
>               if (flag){
>                       UDR = 'A';  //print a character to prove that the
> flag was set.
>               }
>       }
> }
> 
> 
> 
> 
> _______________________________________________
> AVR-GCC-list mailing list
> address@hidden
>
http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
> 


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