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RE: [Tsp-devel] Alignment error on VxWorks
From: |
TSP |
Subject: |
RE: [Tsp-devel] Alignment error on VxWorks |
Date: |
Thu, 27 Nov 2008 17:05:51 +0100 |
Hi all Freds and others
OK thanks for answering so fast Stephane and Fred (nice name by the
way).
Stop me if I'm wrong : BB is a big shared malloc and when we call
bb_publish,data is written "manually" into it and return the address of the
first byte ?
I've checked this issue on vxworks and it appears there is
a function (memalign ) which forces the allocated buffer to starts on a memory
adress evenly divisible by a parameter ( power of 2 ).I could use it instead
of a simple malloc.
If what I said above is what is done in BB (write
manually the data in the "malloced" shmem), I don't think there is any chance
to work, right ?
I think I will try to modify bb_publish to handle
alignment issue but everything I see to solve this is "to fill the blank".I
mean add an offset in order to make the following addresses begin at the right
value (e.g divisible by 4).Ot course, it leads to a waste of memory.There is
an other method ?
As far
as I am concern, I don't think that manually forcing align on 4 or 8 bytes in
bb_publish won't be a big waste.
It
will only happens when U2 are followed U64, and will charge memory of 16 bytes
instead of 10 bytes. So the worst case (U2 => U64) *n would only takes 60%
more than the minimum.
And I
think it will be much more faster than any copy byte per byte, and I'm not even
sure that you can implement it with BB concept
(Pointers returns by bb_publish are like pointers from malloc, and users
can play with them as they want)
But if
you implement that kind of strict align in BB, please keep it configurable from
1 to 8 bytes.
Yves
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RE : [Tsp-devel] Alignment error on VxWorks, Arquer Stephane, 2008/11/27