Re: [lwip-users] Ang: Re: Bare Metal / Memory Alignment

[vincent cui]

Simon:

Do you try the test for web server for my test description ?

锘?Vincent Cui
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-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Simon Goldschmidt
Sent: 2011年9月8日 4:35
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Ang: Re: Bare Metal / Memory Alignment

Kieran Mansley <address@hidden> wrote:

> 
> On 7 Sep 2011, at 16:59, address@hidden wrote:
> 
>> I recently got the impression that structure-packing wasn't mandatory and 
>> could be replaced with padding, I'm not at all sure about this
> 
> I think structure packing is the only sensible way of ensuring you get 
> correct behaviour.

> 
Most protocol headers happen to be aligned correctly for 32-bit processors if 
you insert 2 bytes before the Ethernet header. However, that's not supported by 
us, currently. So if it works, it does so by chance... If you get it to work 
without packing, you're lucky enough, but I doubt that it has too big of an 
influence on throughput, as many header members are only read once.

Simon
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