Lpc2000

Sorry. I meant the lsb.

Guille

--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
<yahoo.messenger@m...> wrote:
>
> I thought that using the msb to switch between ARM/Thumb was common 
> to BL and BX. Now I see it's not. Thanks a lot, Karl, because I was 
> about to run into that very pit myself!
> 
> Guille
> 
> --- In lpc2000@yahoogroups.com, "Karl Olsen" <kro@p...> wrote:
> >
> > ---- Original Message ----
> > From: "Guillermo Prandi" <yahoo.messenger@m...>
> > To: <lpc2000@yahoogroups.com>
> > Sent: Saturday, October 29, 2005 2:22 AM
> > Subject: [lpc2000] Re: LPC2138FBD64 - not possible to run from 
Flash
> > and use IAP?
> > 
> > > Karl, I'm an LPC newbie so please excuse my silly question but, 
> why
> > > not just...?
> > >
> > > void (*CallIAP)(unsigned int *cmd, unsigned int *resp) = 
> 0x7ffffff1;
> > >
> > > void My Func()
> > > {
> > >   .
> > >   .
> > >   CallIAP(cmd, resp);
> > >   .
> > >   .
> > > }
> > >
> > > What does the assembler routine you wrote do different from 
this?
> > 
> > The above works when you have enabled interworking.  I think that 
> Keil
> > always uses interworking.  GCC only uses it when you enable it
> > by -mthumb-interwork.
> > 
> > With interworking, the compiler always uses the mode-switching BX
> > instruction for returns and indirect calls.  (For direct calls it 
> uses a
> > normal BL, and when the caller and callee are different mode, the 
> linker
> > then inserts a small piece of code between them that switches 
> mode).  Using
> > BX for returning often produces less efficient code.
> > 
> > Using the CallIAP assembler routine means that you can avoid
> > -mthumb-interwork, and only use BX in the single place it is 
> needed, i.e.
> > when calling the IAP entry point (assuming that the whole program 
> is in ARM
> > mode).
> > 
> > Karl Olsen
> >
>