RTEMS stack + TSIM-LEON2 weird behaviour

[Joel Sherrill]

Jiri Gaisler wrote:
> The SPARC BSP start-up is discussed in this Wiki article:
>
> http://www.rtems.com/wiki/index.php/SparcBSPStartup
>
> In particulary, see the first paragraph:
>
> "The SPARC port of RTEMS generates binaries that do not perform any board initialisation, and that
> are linked to the beginning of the RAM. The idea behind this is to avoid having a separate bsp for
> every possible board around. Instead, a boot-prom builder (mkprom) is used to create a
> self-extracting prom image that initialises all board registers, loads the application to ram, and
> the starts it. The parameters to mkprom defines memory sizes, waitstates, frequency, stack pointer
> and so on."
>   
OK.  So that says the other thread should be writing a boot loader
that runs before RTEMS.
> When running a RAM image in TSIM, the simulator will recognize that no initialization
> has been done, and automatically set the stack pointer, %psr and some other registers
> to sane values. I do not see any reason why this should be changed. If you want a bsp
> that does the initialization and start-up, I suggest that you create a new bsp rather
> that modify the existing one. However, note that a SPARC V8 processor starts at address
> 0 (in PROM), so you will need to load some code in PROM as well to be able to jump to
> the RAM image.
>   
I don't disagree.  But why is the stack pointer set the way it is in 
start.S? 
It assumes some value is in %sp from the invoking environment.  If that
isn't 0, it looks to me that the code doesn't work.

--joel
> Jiri.
>
>
>
> Joel Sherrill wrote:
>   
>> Aitor.Viana.Sanchez at esa.int wrote:
>>     
>>>       
>>>> The initial value of %sp seens to be 0 on the sparc configurations I
>>>>         
>>> have.
>>>       
>>>> So the sub instruction you highlighted above would set the %sp to
>>>> the area below the work space.
>>>>         
>>>> This code hasn't changed in a LONG time and makes assumptions about
>>>> the execution environment which I cannot personally guarantee.  Jiri
>>>> would be able to do so.
>>>>         
>>> i am pretty sure (Jiri will correct me if I am wrong) that TSIM
>>> initializes %sp and %fp to allow direct RAM execution in case the SW
>>> does not have a bootstrap SW behind (e.g. mkprom)
>>>
>>>       
>>>> My first thought this morning is that this may have been a valid
>>>>         
>>> assumption
>>>       
>>>> at one time (initial %sp is 0) but with more variations and starting
>>>> environments,
>>>> it may not be valid anymore.  I would guess that the "sub" statement
>>>>         
>>> would
>>>       
>>>> be better changed to a "mov %l3, %sp" and ignore the inherited %sp.
>>>>         
>>> I think this a good solution.
>>>
>>>       
>> It is certainly simple.  We need confirmation from Jiri or Daniel.
>>     
>>> Regards,
>>>
>>> Aitor
>>>
>>>
>>>       
>>     


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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