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RE: Simple Redboot Q's


In fact it turns out that most of the code I'm trying to run is fine
(and position independent). 
Where it falls down is in the interrupt setup which isn't position
independent. 
My code (wrongly) assumes that the interrupt vector is pointing to it's
own ISRs whereas interrupts are in fact being handled by Redboot.
Fortunately I had written the setup code for interrupts within Redboot
and put a bit of code to flash an led whenever the hal_IRQ_handler fun
was called or it would have taken me ages to realise what was going on.
I guess I have two choices here; If I want to make use of interrupts in
Redboot (not sure if flash needs them) I'd have to pass them on to my
own app's ISRs when appropriate. If I don't need Redboot interrupts then
I could just not set them up in Redboot? I couldn't find a switch in the
configtool, so that's probably the way to do it.

Many thanks to Andrew and Gary who have had the patience to prod me in
the right directions.

m@

-----Original Message-----
From: Andrew Lunn [mailto:andrew@lunn.ch] 
Sent: 26 July 2005 18:22
To: Matt Sartori
Cc: eCos Discussion
Subject: Re: [ECOS] Simple Redboot Q's


On Tue, Jul 26, 2005 at 06:03:51PM +0100, Matt Sartori wrote:
> Yes, that all the jumps and references within the code are relative, 
> not absolute.

Nope. eCos is position dependant. ie you have to load it where it
expects to be loaded. Otherwise it crashes and burns.

> I think what I'm not quite understanding is what the load does.
> I would expect the loading of an elf to involve the interpretation of
> the file as to where to put it (and probably other stuff), however
> loading an elf explicitly to a location (with -b) doesn't make logical
> sense to me since the elf already knows where it wants to go. 

Correct. You should not tell the loader where to put the image. You only
need this for raw binaries. That format does not contain the position
information so you have to tell it.

> Equally baffling to me is when I load a .bin to an explicit location 
> then I can't just run it from that location.
>
> Only when I load the .bin into the same memory location as what I've 
> put in the binary's linker script does it work

Thats the position independant stuff again... You code appears not to be
position independant. It contains absolute addresses, not relative
addresses. Hence when its in the wrong place it crashes an burns.

If you want to be able to load your application to any random address
you need to make your application position independant. This can be
quite difficult, so most applications don't do it.

        Andrew

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