ip_hdr._ttl_proto is 16 bits long, but this includes both the TTL and
the protocol bits. 


Jared

 

From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Muhamad Ikhwan Ismail
Sent: Tuesday, December 11, 2007 23:00
To: [email protected]
Subject: [lwip-users] The purpose of structure packing

 

Hi,
I swear i searched the mailing list before coming up with this question,
and none really explains the purpose of structure packing.


My question is what is the purpose of structure packing. I at first
thought  lwip requires it to spare memory and
keep alignment problem away, and since I dont have much of those problem
I removed all of my structure packing macros.
I am working with lwip 1.2.0.

I was checking the pbufs of the DHCP discovery packet since wireshark
couldnt pickup any of the packages i transmitted.
The driver was working since the ethernet controller signals that the
buffer was sent. Then I noticed that e.g in RFC that the IP header
member e.g TTL should be 8 bits long while in struct ip_hdr it is 16
bits long, and in the pbufs prior to transmission it was also 16 bits
long.
Hence I assumed which is why wireshark didnt pick the package up or it
was filtered by the end point ethernet controller.
I guess that this is due to the fact I removed structure packing ?
Anyone with example done with a Windriver compiler ?

Thanks a lot for your replies.

Greetings
M Ikhwan

 

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