I think You want something, like
union{
int a;
struct{
char b;
char c
}data
}x;
On Monday 03 of January 2005 07:16, Venkata, Bulusu (IE10) wrote:
> Hi,
> I'm having problems with packed structures. Given below is a sample
> code("test.c") which uses a packed structure:
>
> #include <stdio.h>
> typedef struct {
> char a;
> int b;
> }__attribute__((packed)) unaligned_struct;
>
> unaligned_struct hg;
> char dummyVar;
>
> void main(void){
> unaligned_struct* ptr=&hg;
>
> hg.a = 0x56;
> hg.b = 0x1234;
> }
>
>
> The equivalent assembly code generated was as follows:
>
> - 0x1140 <main>: mov #2558, SP ;#0x09fe
> - 0x1144 <main+4>: mov r1, r4 ;
> 13 unaligned_struct* ptr=&hg;
> - 0x1146 <main+6>: mov #514, 0(r4) ;#0x0202
> 14
> 15 hg.a = 0x56;
> 0x114c <main+12>: mov.b #86, &0x0202 ;#0x0056
> 16 hg.b = 0x1234;
> - 0x1152 <main+18>: mov #4660, &0x0000 ;#0x1234
> - 0x1158 <main+24>: incd SP ;
> - 0x115a <main+26>: br #0x115e ;
>
> The msp430-gcc compiler gives an error/warning at line no. 16, (i.e. at
> hg.b = 0x1234;):
> test.c:16: internal error: unsupported relocation error
>
> However, when I tried the same with the IAR compiler, it works fine. I
> guess MSPGCC doesn't guarantee support for packed structures due to the
> problems MSP430 has with unaligned word accesses - so how does IAR do it? I
> apologize for the long post, but I desperately need to use packed
> structures in my code. Thank you..
>
> Regards,
> Sudhakar
>
>
>
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