Lpc2000

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.
>
> I had a bug in my app this way that happened because of this.  It was
> strange, I traced it down to writing a value almost like this, and my debug
> code did:
>
> void dummyCall(long *lp)
> {
>    foo = *lp;
> }
>
> long foo, bar, *lp;
>
> HexDump(b,4);
>
> lp = (long *)b
> bar = *lp;
> dummyCall(&bar);
> *lp = bar;
>
> HexDump(b,4);
>
> What was happening is the first and last halves of the 4-byte segment at b
> were swapping (i.e. 0xAABBCCDD became 0xCCDDAABB) and I couldn't for the
> life of me figure out why, until I realized that b wasn't on a 4-byte
> boundary.
>
> The reason for the dummy call was because otherwise the compiler is because
> when I did this:
>
> bar = *lp;
> *lp = bar;
>
> The compiler actually didn't compile that code.
>
> -- 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.
> >
> >
> >SPONSORED LINKS
> ><http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microcontrollers&
> >w2=Microprocessor&w3=Intel+microprocessors&w4=Pic+microcontrollers&c=4&s=9
> >5&.sig=mfaAujKZXA2Z_vxre9sGnQ>Microcontrollers
> > <http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microcontrollers&w
> >2=Microprocessor&w3=Intel+microprocessors&w4=Pic+microcontrollers&c=4&s=95
> >&.sig=9jjd2D3GOLIESVQssLmLsA>Microprocessor
> > <http://groups.yahoo.com/gads?t=ms&k=Intel+microprocessors&w1=Microcontro
> >llers&w2=Microprocessor&w3=Intel+microprocessors&w4=Pic+microcontrollers&c
> >=4&s=95&.sig=OMnZuqMZX95mgutt4B-tDw>Intel microprocessors
> ><http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microcontroll
> >ers&w2=Microprocessor&w3=Intel+microprocessors&w4=Pic+microcontrollers&c=4
> >&s=95&.sig=Malspbd0T4Rq3M4Q0nHrfw>Pic microcontrollers
> >
> >
> >----------
> >YAHOO! GROUPS LINKS
> >
> >    *  Visit your group "<http://groups.yahoo.com/group/lpc2000>lpc2000"
> > on the web.
> >    *
> >    *  To unsubscribe from this group, send an email to:
> >    *
> > <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe>lpc2000-u
> >nsubscribe@yahoogroups.com
> >
> >    *
> >    *  Your use of Yahoo! Groups is subject to the
> > <http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.
> >
> >
> >----------
>
> Yahoo! Groups Links
>
>
>