blob-cvs-commit

start.S and ld-script

[Yamijala S. <Sri...@si...>]

Hi All !
 
I find that in blob/src, there are these files: start.S and ld-script.
In ld-script, there is the declaration for _start (i suppose _start is a
symbol) as:
 
ENTRY(_start)
 
I understand that _start is a global and is required by the linker to
specify the first instruction
to be executed in a program.The corresponding code in blob is:
 
.globl _start
_start: b reset
 b undefined_instruction
 b software_interrupt
 b abort_prefetch
 b abort_data
 b not_used
 b irq
 b fiq
 
reset:
- - - - -
- - - - -
- - - - -
 
So, In blob the first instruction to be executed is the one in the reset
label of start.S
 
Now, could someone please clarify the following queries:
 
After a H/W Reset, the instruction at address 0x00000000 is executed.
In the SA-1110 manual, it has been mentioned that this address corresponds
to the static memory selected by
nCS0.Let me say, it is a Flash memory. 
 
In blob, I found a comment that "The SA-1110 jumps to address 0x00000000
after a reset. 
We put a single branch code at this position, which jumps to a safe region
to do the actual setup".
 
Also, in the SA-1110 manual, it has been given that 0x00000000 is the reset
vector address.
This means this is the first location where our processor should step into.
 
So, is my assumption true that the flash is mapped to Static memory bank 0
of SA-1110 from addresses 0x00000000 and that
_start: b reset
 
is the first instruction to be executed after a reset?
 
Moreover, how are the other branches namely: undefined_instruction,
software_interrupt etc. mapped in S/W to the actual vectors?
when/how is the first branch to these labels taken?
 
Thank You
Sridhar

Re: start.S and ld-script

[<ste...@el...>]

On Wed, Nov 19, 2003 at 05:18:46PM +0530, Yamijala Sridhar wrote:
> Hi All !
>  

Hi.

[snip]
>  
> After a H/W Reset, the instruction at address 0x00000000 is executed.
> In the SA-1110 manual, it has been mentioned that this address corresponds
> to the static memory selected by
> nCS0.Let me say, it is a Flash memory. 
>  
> In blob, I found a comment that "The SA-1110 jumps to address 0x00000000
> after a reset. 
> We put a single branch code at this position, which jumps to a safe region
> to do the actual setup".
>  
> Also, in the SA-1110 manual, it has been given that 0x00000000 is the reset
> vector address.
> This means this is the first location where our processor should step into.
>  
> So, is my assumption true that the flash is mapped to Static memory bank 0
> of SA-1110 from addresses 0x00000000 and that
> _start: b reset
>  
> is the first instruction to be executed after a reset?

I am not exactly a Hardware guy, but as I understand things you're correct.

> Moreover, how are the other branches namely: undefined_instruction,
> software_interrupt etc. mapped in S/W to the actual vectors?
> when/how is the first branch to these labels taken?

These are jumped to when the processor encounters the corresponding exception,
for example "undefined instruction" etc.

As I understand it, these vectors are only used in BLOB, for example
Linux defines them differently.

>  
> Thank You
> Sridhar

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