GCC not awre of MMU

GCC not awre of MMU

[Schaefer Philipp]

Hello,
 I am using: GCC
Configured with: ../gcc-3.0.4/configure --target=powerpc-ibm-eabi
--with-newlib
i686-ibm-cygwin
Thread model: single
gcc version 3.0.4

I am porting a firmware to PPC 403cr
an I am using Memory Management Unit MMU to access litle endian Hardware.

The MMU is configured to have both Big-endian and Little endian Spaces.

Now to my Problem:

I have a code line like :

short a = (short)((PointerToMyStruct->ALongValue)+5);

this generates for Power PC
a Assamblercode like :(Pseudo Code)
Load lower halfword from ALongValue to Register 9 
add 5 to register 9
save lower halfword in a;

But this Code would work only Correct If  there would not be a MMU wich
swaps Litle Endian to Big-endian Values in some part of Memory !!!
Is there a Posibility to tell GCC there is a MMU so he can not predict the
endiness  and generate Code like:
(Pseudo Code)

Load WORD (not halfword!) from ALongValue
Add 5
store lower half word in a.



Thank You Very much !








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Re: GCC not awre of MMU

[Jim Wilson]

Schaefer Philipp wrote:
> But this Code would work only Correct If  there would not be a MMU wich
> swaps Litle Endian to Big-endian Values in some part of Memory !!!

Try declaring the object as volatile.  Gcc won't change the memory 
access size for references to volatile objects, so it will load an 
entire word from memory and then convert to a short within the register.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com