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Re: Linker sections & network buffers question.


Will Wagner wrote:
> Gary,
> 
> Yes that seems to work great.
> 
> Do you have any idea about whether the net memory pools need to be in
> the bss section in the first place?

Probably not, but it would take some effort to get them into a different
section.

> Gary Thomas wrote:
>> Will Wagner wrote:
>>> Hi All,
>>>
>>> Have hit a problem where in debug builds the initialisation of the bss
>>> section to zero takes so long that the chip watchdogs.
>>>
>>> I'm using an MPC866 chip and one of the problems with it is that the
>>> slowest I can set the watchdog to is just over 0.5secs. The bss section
>>> is just under 3MB and most of that (2MB) are the networking buffers.
>>>
>>> So I have a whole load of questions for you:
>>>
>>> Do the network buffers really have to reside in the bss section. The
>>> buffers are just used to create Mempools and looking at the code I don't
>>> think it relies on the memory being zero'd.
>>>
>>> If the buffers don't need to reside in the bss section, anyone know
>>> which section is the one for variables that don't get set to zero?
>>> Anyone remind me of the gcc syntax for specifying which section
>>> something goes in?
>>>
>>> On powerpc in vectors.S the sbss & bss sections are zero'd before the
>>> cache & mmu are enabled which means that the access to the SDRAM will
>>> not burst (I think) and so be much slower. Any reason for not
>>> rearranging the code so that cache & mmu are enabled before we try to
>>> zero sbss & bss?
>>
>> Sorry, this won't work as much of the code (including the part that
>> sets up the MMU) is written in C and will expect the BSS to have already
>> been cleared.
>>
>> Try the attached patch which uses a different sequence to clear the BSS.
>> It should run quite a bit faster (2 instructions / word instead of 4).
>>
>> BTW, if this works for you, let me know and I'll check it in.
>>
>>
> 


-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------

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