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

[Ned Konz]

On Friday 12 March 2004 5:48 am, Andreas Becker wrote:
> static volatile _RX_BUFFER      *_rx_decode_buffer;
>
> SIGNAL(SIG_ADC)
> {
>         _rx_decode_buffer++;
> }


With your declaration and -O1:
static volatile _RX_BUFFER      *_rx_decode_buffer;

  26:test2.c       ****         while(1)
  98                    .LM5:
  99 0036 8091 0000             lds r24,_rx_decode_buffer
 100 003a 9091 0000             lds r25,(_rx_decode_buffer)+1
 101                    .L9:
  27:test2.c       ****         {
  28:test2.c       ****                 if (_rx_decode_buffer != NULL)
 103                    .LM6:
 104 003e 0097                  sbiw r24,0
 105 0040 F1F3                  breq .L9
  29:test2.c       ****                 {
  30:test2.c       ****                         _rx_decode_buffer = NULL;
 107                    .LM7:
 108 0042 80E0                  ldi r24,lo8(0)
 109 0044 90E0                  ldi r25,hi8(0)
 110 0046 FBCF                  rjmp .L9
  31:test2.c       ****                 }
  32:test2.c       ****         }
  33:test2.c       **** }

With the declaration:
static _RX_BUFFER      *volatile _rx_decode_buffer;

 26:test2b.c      ****         while(1)
  27:test2b.c      ****         {
  28:test2b.c      ****                 if (_rx_decode_buffer != NULL)
  99                    .LM5:
 100 0036 8091 0000             lds r24,_rx_decode_buffer
 101 003a 9091 0000             lds r25,(_rx_decode_buffer)+1
 102 003e 892B                  or r24,r25
 103 0040 D1F3                  breq .L8
  29:test2b.c      ****                 {
  30:test2b.c      ****                         _rx_decode_buffer = NULL;
 105                    .LM6:
 106 0042 1092 0000             sts (_rx_decode_buffer)+1,__zero_reg__
 107 0046 1092 0000             sts _rx_decode_buffer,__zero_reg__
 108 004a F5CF                  rjmp .L8
  31:test2b.c      ****                 }
  32:test2b.c      ****         }
  33:test2b.c      **** }

But I think you probably mean that the pointer *and* what it points to are 
both being changed by the interrupt routine, in which case you *really* want:

static volatile  _RX_BUFFER *volatile _rx_decode_buffer;


-- 
Ned Konz
http://bike-nomad.com
GPG key ID: BEEA7EFE

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