Re: [Mspgcc-users] It seems that the C compiler overwrites registers !!!

[Garst R. Reese]

Hi Thln, I'm no expert, but the most common reason for this sort of 
thing is gcc optimization, and the most common cure is to declare the 
index volatile, so you might try declaring i volatile.

Hope it helps,
Garst
thln wrote:

Hi,
 
 
Thanks, Chris Liechti, for your help about _Re: Help about sizeof( 
struct ...) MSP430-GCC_  (2005-04-26 16:46)  
 
So, if i write the fowling function (Swap_TAB_UART), the result is not 
good.
the function lose len, ix values.
 
It seems that the C compiler overwrites registers !!!
 
 
 
Kind Regards, Thln!
 
 
 
void Swap_TAB_UART(unsigned char ix, unsigned char len)
{
unsigned char i, tmp, l;
 
l = len/2;
i = 0;
do
  {
  tmp = TAB_UART[ix+i];
  TAB_UART[ix+i] = TAB_UART[ix+len-i-1];
  TAB_UART[ix+len-i-1] = tmp;
  i++;
  } while (i<l);
}
 
void main(void)
{
 
 
TAB_UART[15] = 0xC1;
TAB_UART[16] = 0x20;
TAB_UART[17] = 0x00;
TAB_UART[18] = 0x00;
 
 Swap_TAB_UART(15, 4);
}
 
 
 
 
 
 
 
void Swap_TAB_UART(unsigned char ix, unsigned char len)
{
    cd10: 0b 12        push r11  ;
    cd12: 0a 12        push r10  ;
    cd14: 09 12        push r9  ;
    cd16: 08 12        push r8  ;
    cd18: 04 12        push r4  ;
    cd1a: 4d 4f        mov.b r15, r13 ; R13 = ix
    cd1c: 4f 4e        mov.b r14, r15 ; R15 = len
unsigned char i, tmp, l;
 
l = len/2;
    cd1e: 49 4e        mov.b r14, r9 ;
    cd20: 12 c3        clrc   
    cd22: 49 10        rrc.b r9  ;    R9= len/2
i = 0;
    cd24: 4c 43        clr.b r12  ;    R12=i
    cd26: 4e 4d        mov.b r13, r14 ;
    cd28: 7f f3        and.b #-1, r15 ;r3 As==11
do
    cd2a: 38 40 20 02  mov #544, r8 ;#0x0220
    cd2e: 0a 4e        mov r14, r10 ;    
    cd30: 0a 58        add r8, r10 ;   R10=ix+220
    cd32: 0b 4e        mov r14, r11 ;
    cd34: 0b 5f        add r15, r11 ; R11 = ix+len
  {
  tmp = TAB_UART[ix+i];
    cd36: 4f 4c        mov.b r12, r15 ; len is lost !
    cd38: 0e 4a        mov r10, r14 ;   ix is lost ! 
    cd3a: 0e 5f        add r15, r14 ;
    cd3c: 6d 4e        mov.b @r14, r13 ; ix is lost !
  TAB_UART[ix+i] = TAB_UART[ix+len-i-1];
    cd3e: 04 4b        mov r11, r4 ;
    cd40: 04 8f        sub r15, r4 ;
    cd42: 0f 44        mov r4, r15 ;
    cd44: 0f 58        add r8, r15 ;
    cd46: de 4f ff ff  mov.b -1(r15),0(r14) ;
    cd4a: 00 00
  TAB_UART[ix+len-i-1] = tmp;
    cd4c: cf 4d ff ff  mov.b r13, -1(r15) ;
  i++;
    cd50: 5c 53        inc.b r12  ;
  } while (i<l);
    cd52: 4c 99        cmp.b r9, r12 ;
    cd54: f0 2b        jnc $-30      ;abs 0xcd36
}
    cd56: 34 41        pop r4  ;
    cd58: 38 41        pop r8  ;
    cd5a: 39 41        pop r9  ;
    cd5c: 3a 41        pop r10  ;
    cd5e: 3b 41        pop r11  ;
    cd60: 30 41        ret