Re: [ECOS] Linker sections & network buffers question.

[Will Wagner <will_wagner@carallon.com>]

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?

Thanks,

Will.

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.
> 
> 

-- 
------------------------------------------------------------------------
Will Wagner                                     will_wagner@carallon.com
Senior Project Engineer                  Office Tel: +44 (0)20 7371 2032
Carallon Ltd, Studio G20, Shepherds Building, Rockley Rd, London W14 0DA
------------------------------------------------------------------------



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