[lwip-users] The purpose of structure packing

[Muhamad Ikhwan Ismail]

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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