Re: [avr-gcc-list] Why are we using EICALL and EIJMP for AVR256?

[andrewhutchinson]

Thanks, it would be nice if this was documented.

I noticed it when reviewing addressing modes and a omission in call patterns.

void  (*fptr)();

fptr = main;

(*fptr)();  //Will use EICALL - should be CALL main


which become readily apparent with inlined code.


Andy



---- Sean D'Epagnier <address@hidden> wrote: 
> On 12/14/09, Andrew Hutchinson <address@hidden> wrote:
> > The patterns for AVR mega 256 use EICALL an EIJMP
> >
> > Both require EIND to be set to provide upper address bits
> >
> > However, we are using linker trampolines for both, so in either case the
> > 16 bit jump or call is to the trampolines.
> >
> > Are not the trampolines always located in first 128Kbytes? Thus we
> > should be using ICALL and IJMP and not needing to set use EIND at all.
> >
> > What have I miss-understood?
> >
> 
> Hi,
> 
> Yes this confused me a lot too, but the reason is because the
> trampoline is not in the first 128kbytes for a bootloader, so if the
> compiler uses eijmp and eicall, then it is possible to do indirect
> calls there too, but it still works fine in normal code.
> 
> Sean
> 
> >
> > Andy
> >
> >
> >
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> >