[ECOS] Error when write a uint32 with not aligned pointer.

[ECOS] Error when write a uint32 with not aligned pointer.

[wang cui]

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Hi, compiler and ARM experts:

I am faceing a problem like below:

Arch of my target is arm7tdmi(lpc2xxx), little endian.

When I use a (cyg_uint32 *)ptr to write a 32bit value, it always error if 
the ptr is not 4-byte aligned.

For example:
ptr = 0x8106409a;
*ptr = 0x00000001;

The result is not like:
0x81064098: 0xXX - shouldn't be modified
0x81064099: 0xXX - shouldn't be modified
0x8106409a: 0x01
0x8106409b: 0x00
0x8106409c: 0x00
0x8106409d: 0x00
but
0x81064098: 0x01
0x81064099: 0x00
0x8106409a: 0x00
0x8106409b: 0x00
0x8106409c: 0xXX - should be modified
0x8106409d: 0xXX - should be modified

It always cause problem when I use tcpip stack.(not cause problem for other 
packages with luck)

So how to solve it? Should I modify some compiling options?

Thanks in advance!

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Ãâ·ÑÏÂÔØ MSN Explorer:   http://explorer.msn.com/lccn  


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Re: [ECOS] Error when write a uint32 with not aligned pointer.

[Gary Thomas]

wang cui wrote:
> Hi, compiler and ARM experts:
>
> I am faceing a problem like below:
>
> Arch of my target is arm7tdmi(lpc2xxx), little endian.
>
> When I use a (cyg_uint32 *)ptr to write a 32bit value, it always error
> if the ptr is not 4-byte aligned.
>
> For example:
> ptr = 0x8106409a;
> *ptr = 0x00000001;
>
> The result is not like:
> 0x81064098: 0xXX - shouldn't be modified
> 0x81064099: 0xXX - shouldn't be modified
> 0x8106409a: 0x01
> 0x8106409b: 0x00
> 0x8106409c: 0x00
> 0x8106409d: 0x00
> but
> 0x81064098: 0x01
> 0x81064099: 0x00
> 0x8106409a: 0x00
> 0x8106409b: 0x00
> 0x8106409c: 0xXX - should be modified
> 0x8106409d: 0xXX - should be modified
>
> It always cause problem when I use tcpip stack.(not cause problem for
> other packages with luck)

How so? The TCP/IP stacks should take care to never try this.

>
> So how to solve it? Should I modify some compiling options?

This is a well known problem on ARM; such operations are undefined (some
chips/cores
may throw an exception, but in general they just quietly do the wrong
thing). The only
real solution is to just not try to perform unaligned operations of this
sort.

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


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Re: [ECOS] Error when write a uint32 with not aligned pointer.

[wang cui]

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>How so? The TCP/IP stacks should take care to never try this.

Well, actually, TCP/IP stacks are fine, I faced this problem when I use 
vnc_server package.
It does cause problem on my target. So I have to modify it.
See patch please.

>This is a well known problem on ARM; such operations are undefined (some
>chips/cores
>may throw an exception, but in general they just quietly do the wrong
>thing). The only
>real solution is to just not try to perform unaligned operations of this
>sort.

Ok, got it!

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