Re: Porting eCos to the BlackFin processor

[Jonathan Larmour <jifl at eCosCentric dot com>]

Bas Vermeulen wrote:
> > The linker script sets an entry point, although that tends to be relevant 
> > only for programs that are loaded to and start from RAM. For stuff that 
> > runs from ROM/Flash i.e. that is the first thing that's loaded, then you 
> > have to use the linker script to ensure the relevant startup code is 
> > linked at the correct memory address. This is done by a combination of the 
> > .ld file supplied by the architecture HAL (generally) and the mlt*.ldi/.h 
> > files in the include/pkgconf subdirectories of platform HALs.
>
> Ok. So if I understand you correctly, I don't have to set the CPU's
> reset vector until I'm in my startup routine, because the reset vector
> is handled by ld scripts. Or rather, the startup routine is linked in
> the right memory location.

Yep, because something has to have it running from the right place before 
it can do anything else obviously! For RAM startup apps, the entry point 
can be slightly different: the entry point comes from the first .text bits 
in whatever filename is referenced by the STARTUP() directive in the .ld 
file. Normally this would be
STARTUP(vectors.o)
and the first text stuff in vectors.o would be the startup. Again have a 
look at the other architectures to see what I mean.

You would make this startup routine common between ROM and RAM startup 
anyway. Sometimes other helper functions go in there, but usually those go 
in either arch.inc or <architecturename>.inc (e.g. arm.inc) and are 
defined as macros.

> I think that vector.S needs to contain the interrupt trampoline
> routines, the startup function, and the reset vector. Is there anything
> more than that?

That very much depends on the architecture! If (synchronous) exception 
trampoline routines are different from interrupt ones, then those should 
be there too.

Jifl
--
eCosCentric    http://www.eCosCentric.com/    The eCos and RedBoot experts
--["No sense being pessimistic, it wouldn't work anyway"]-- Opinions==mine