Lpc2000

Dmitry:

Probably yes, check out the assembler listing file when you compile the 
source code.  I don't have the Keil compiler so I can't check it.  I'd 
assume it either did a memcpy or perhaps STMIA/LDMIA assembler instructions.

If you needed to do that in gcc then I believe that memcpy(a,b,4) would 
achieve the same result.  I don't know if there is any direct equivalent to 
__packed in gcc when casting variables.

IIRC isn't left-hand side casting behaviour "undefined" as per the C 
specifications?  I know it's convention to allow left-hand casting, but I 
don't think it's part of the C specifications.

In gcc you can do structure packing like this:

// Master Boot Record
typedef struct {
          unsigned char fill[0x1be];      // boot code
          PARTENTRY partitions[4];        // partition table
          unsigned char sig_55;           // 55h boot signature
          unsigned char sig_aa;           // AAh boot signature
} __attribute__((packed)) MBR, *PMBR;

-- Sean


At 05:40 2/7/2006, you wrote:
>Sean,
>does it mean that
>       *(__packed long *) a = *(long *)b;
>is actually
>       memcpy(a,b,4)
>???
>
>Cheers,
>Dmitry.
>
>On Tuesday 07 February 2006 13:25, Sean wrote:
> > Dmitry:
> >
> > __packed means that there will be no gaps left around that
> > variable.  Normally a long would be put on a 32-bit boundary, however the
> > __packed attribute tells the linker not to leave any adjacent space.
> >
> > Note that on the ARM7 chips if you attempt to access a halfword or word
> > that is not aligned properly the behaviour is "undefined".  If 'a' is not
> > properly aligned that statement would not work.  In this case this __packed
> > instructs the compiler that 'a' may not be aligned, so read/write it as a
> > series of 4 bytes instead of a directly as a 32-bit word.
> >
> > -- Sean
> >
> > At 04:26 2/7/2006, you wrote:
> > >Hi Bertrik,
> > >
> > > > Making the examples work with GCC involved byte-packing all USB related
> > > > structures and replacing compiler specific options with GCC
> > > > equivalents.
> > >
> > >Thanks a lot...
> > >
> > >I looked into KEIL's examples and found __packed keyword which appeared in
> > >the from of 'long'. I'm puzzled there, for example:
> > >
> > >char *a, *b;
> > >
> > >*(__packed long *) a = *(long *)b;
> > >
> > >how to interpret this???
> > >
> > >Cheers,
> > >Dmitry.