gcc 4.6.1 messes up code ?? why

[andy_code]

i have used volatile & register, but gcc still insists upon this


Ilya Enkovich wrote:
> 
> Hi,
> 
> Do you use 'volatile' type qualifier to prevent undesirable
> transformations of FPGA registers reading code?
> 
> BR
> Ilya
> 
> 2011/8/1 andy_code <andy_code@mailup.net>:
>>
>> hi,
>>
>> I have a function I wrote that part of a keypad reading interrupt for an
>> embbed os we have written for coldfire processors
>> in this function the code reads an FPGA that controls the interrupt, it
>> should only read it once any more and
>> it would confuse the FPGA.
>>
>> here is the original function
>>
>> void keypad_isr(void)
>> {
>>    /*  read a character from the key buffer */
>>    FPGA_UART_DATA              *ptr;
>>    FPGA_UART_DATA              kpd;
>>    int                                 g;
>>    int                                 n;
>>    KEYBUFFER                   *kb;
>>    char                                ch;
>>
>>    kb  = &key_buffer;
>>    asm(" halt");          /* just for debugging */
>>    ptr = FPGA_UART;   /* make a pointer to the FPGA register */
>>    // read upto 8 keys from the keypad
>>    for( n = 0; n < 8 ; n++ )
>>    {
>>        kpd     = *ptr;        /* read from register  (only do this ONCE)
>> */
>>        g = kpd.fifo_cnt;
>>        if(g == 0)
>>            return;
>>        ch = (char) kpd.rx_data;
>>        kb->status = ch;
>>        if( ch != 0 && ch != -1 )
>>        {
>>            if ( kb->current_location >= MAX_KEY_BUFFERS_SIZE-1 )
>>            {
>>                kb->current_location = MAX_KEY_BUFFERS_SIZE-1;
>>            }
>>            kb->key_buff[kb->current_location] = ch;
>>            kb->current_location++;
>>        }
>>    }
>> }
>>
>> ok now here is my problem, gcc does not use an address register for the
>> pointer, and it insists on reading the FPGA directly twice ????
>> here is generated assembly from gcc.
>>
>> keypad_isr:
>>        lea (-12,%sp),%sp
>>        movem.l #1036,(%sp)
>>        move.w -1073741664,%d0         <<<--- should use %a0 surely
>>        clr.l %d1
>>        move.w %d0,%d1                    <<< --- theres the read
>>        moveq #13,%d2
>>        lsr.l %d2,%d1
>>        tst.b %d1
>>        jeq .L3
>>        moveq #8,%d1
>>        lea key_buffer+33,%a1
>>        lea key_buffer,%a0
>>        lea key_buffer+1,%a2
>>        jra .L5
>> .L8:
>>        move.w -1073741664,%d0       <<< --- look its done it again ?????
>>        clr.l %d2
>>        move.w %d0,%d2                  <<< --- ARRRGGGgg its knackered my
>> FPGA
>>        moveq #13,%d3
>>        lsr.l %d3,%d2
>>        tst.b %d2
>>        jeq .L3
>> .L5:
>>        move.b %d0,%d2
>>        move.b %d0,(%a1)
>>        move.l %d2,%d0
>>        addq.l #1,%d0
>>        and.l #255,%d0
>>        moveq #1,%d3
>>        cmp.l %d0,%d3
>>        jcc .L6
>>        clr.l %d0
>>        move.b (%a0),%d0
>>        move.b #30,%d3
>>        cmp.l %d0,%d3
>>        jcc .L7
>>        move.b #31,(%a0)
>> .L7:
>>        move.b (%a0),%d0
>>        clr.l %d3
>>        move.b %d0,%d3
>>        move.b %d2,(%a2,%d3.l)
>>        addq.l #1,%d0
>>        move.b %d0,(%a0)
>> .L6:
>>        subq.l #1,%d1
>>        jne .L8
>> .L3:
>>        movem.l (%sp),#1036
>>        lea (12,%sp),%sp
>>        rts
>>
>> ok how do i stop this happening, thats not the code I wrote.
>> please help, I is tearing my hair out
>>
>> thank you
>> --
>> View this message in context:
>> http://old.nabble.com/gcc-4.6.1-messes-up-code----why-tp32169196p32169196.html
>> Sent from the gcc - Help mailing list archive at Nabble.com.
>>
>>
> 
> 

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