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Re: Optimization problem

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On 2011-05-22 04:47:20 -0400, hamze said:

> On May 22, 12:25 pm, Joshua Maurice <joshuamaur...@gmail.com> wrote:
>> On May 21, 11:29 pm, hamze <hamz...@gmail.com> wrote:
>> 
>>> I have a special device in my system, I must work with it in this
>>> manner that : write 4 bytes and read 3 bytes,
>>> this device has no reset, so if one of reads or writes miss, from that
>>> time device will not work correctly because order of writes and reads
>>> are missed.
>> 
>>> this device works right when optimization is off, but when I turn it
>>> on it stop working properly in my code.
>>> some time i did not use one of its read value, so I think optimization
>>> remove it and order of read and writes are missed.
>>> how can I solve this problem ?
>>> I also test this solution that I defined an asm valotile ( ) and put
>>> all reads and write inside it but still turning optimization on
>>> corrupt my program result.
>> 
>> From what I've heard in this group, volatile alone is insufficient for
>> correct MMIO (memory mapped IO) on most systems. I would suggest
>> looking at the docs for your implementation to see what it says about
>> correct MMIO. You could also look at the output assembly to see if it
>> is indeed not doing as you want.
> 
> thanks alot, you gave me a valuable clue,
> I know what is my hardware correct order of MMIO, but I dont know how
> to make compiler know about it and force compile not to REORDER my
> code.

Since there's no code here, just a bunch of hand-waving, it's 
impossible to say definitively what's going on. But the compiler is not 
allowed to reorder or combine accesses to volatile objects.

-- 
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The 
Standard C++ Library Extensions: a Tutorial and Reference 
(www.petebecker.com/tr1book)

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Optimization problem hamze <hamze60@gmail.com> - 2011-05-21 23:29 -0700
  Re: Optimization problem Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-22 01:25 -0700
    Re: Optimization problem hamze <hamze60@gmail.com> - 2011-05-22 01:47 -0700
      Re: Optimization problem Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-22 11:40 +0000
      Re: Optimization problem Pete Becker <pete@versatilecoding.com> - 2011-05-22 08:39 -0400
      Re: Optimization problem Nobody <nobody@nowhere.com> - 2011-05-22 15:01 +0100
      Re: Optimization problem Geoff <geoff@invalid.invalid> - 2011-05-22 09:14 -0700

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