RE: [avr-gcc-list] GCC problem, volatile

[Dave Hylands]

Hi Andreas,

I believe that you declared the thing that _rx_decode_buffer points to
as being volatile and not the pointer itself.

Read pointer declarations from right to left, and you see that:

    static volatile     _RX_BUFFER      *_rx_decode_buffer;

Is a pointer to a volatile _RX_BUFFER. If you want a volatile pointer
then you need to use:

    static _RX_BUFFER   * volatile _rx_decode_buffer;

If you also want the contents to be volatile, then you need to use:

    static volatile _RX_BUFFER  * volatile _rx_decode_buffer;

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/


> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden On Behalf Of Andreas Becker
> Sent: Friday, March 12, 2004 5:49 AM
> To: address@hidden
> Subject: [avr-gcc-list] GCC problem, volatile
> 
> 
> Hi All,
> 
> I'm using AVR-GCC 3.3.2
> I have got a a problem with the the optimisation the Compiler 
> does. The C File:
> 
> #include <stdlib.h>
> #include <avr/signal.h>
> #define       _RX_BUFFER_SIZE         30
> #define       _RX_BUFFER_NUMBER       5
> 
> typedef struct
> {
>       char    buffer[_RX_BUFFER_SIZE];
>       char    elements;
> } _RX_BUFFER;
> 
> static        _RX_BUFFER      _rx_buffers[_RX_BUFFER_NUMBER];
> 
> static volatile       _RX_BUFFER      *_rx_decode_buffer;
> 
> SIGNAL(SIG_ADC)
> {
>       _rx_decode_buffer++;
> }
> 
> extern        int     main (void)
> {
>       while(1)
>       {
>               if (_rx_decode_buffer != NULL)
>               {
>                       _rx_decode_buffer = NULL;
>               }
>       }
> }
> 
> If I use Optlevel 0 everything works fine.
> 
> ASSEMBLER CODE from the .lss File:
>       while(1)
>       {
>               if (_rx_decode_buffer != NULL)
>   d2: 80 91 fb 00     lds     r24, 0x00FB
>   d6: 90 91 fc 00     lds     r25, 0x00FC
>   da: 00 97           sbiw    r24, 0x00       ; 0
>   dc: d1 f3           breq    .-12            ; 0xd2
>               {
>                       _rx_decode_buffer = NULL;
>   de: 10 92 fc 00     sts     0x00FC, r1
>   e2: 10 92 fb 00     sts     0x00FB, r1
>   e6: f5 cf           rjmp    .-22            ; 0xd2
> 
> 
> If I use Optlevel 1 the Compiler does't reloads the _rx_decode_buffer 
> Pointer.      Compare the Line 0xdc (Optlevel 0) and Line 
> 0xce (Optlevel 1).
> The Destination of the Jump is another. 
> 
> ASSEMBLER CODE from the .lss File:
>       while(1)
>   c4: 80 91 fb 00     lds     r24, 0x00FB
>   c8: 90 91 fc 00     lds     r25, 0x00FC
>       {
>               if (_rx_decode_buffer != NULL)
>   cc: 00 97           sbiw    r24, 0x00       ; 0
>   ce: f1 f3           breq    .-4             ; 0xcc
>               {
>                       _rx_decode_buffer = NULL;
>   d0: 80 e0           ldi     r24, 0x00       ; 0
>   d2: 90 e0           ldi     r25, 0x00       ; 0
>   d4: fb cf           rjmp    .-10            ; 0xcc
> 
> 
> Is it my fault, or is there something wrong with the 
> Compiler?
> 
> -- 
> Dipl.-Ing.(FH) Andreas Becker
> Entwicklung
> 
> dSys e.K.
> Soeflinger Str. 100
> D-89077 Ulm
> Tel:  +49.731.151579-1
> Fax: +49.731.151579-9
> web: www.dsys.de
> 
> _______________________________________________
> avr-gcc-list mailing list
> address@hidden 
> http://www.avr1.org/mailman/listinfo/avr-gcc-> list
> 
> 


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