With blip, there is no need for nx_types to be used, since it is regular
IP/IPv6. Just like we can send structs over UDP using sockets, we can do
the same using blip (or atleast that's my assumption). Since MSP430 is
little endian, I am assuming EPIC is the same as well. netcat picks it
up from the tunnel interface created by ip-driver (tun0, with an IP6 of
fec0::64). To complicate things, I am running ip-driver on a netgear
router, which has a MIPS based CPU, meaning it's big endian.
In short, ip-driver gives a big endian byte order to netcat on the
router, but it gives a little endian order on my PC, with the SAME code
running on the mote.
On 03/03/2011 06:16 PM, Eric Decker wrote:
On Thu, Mar 3, 2011 at 3:16 PM, Harsha Chenji <[email protected]
<mailto:[email protected]>> wrote:
I am trying to work with endianness in the blip/tinyos platform on an
epic mote. The mote sends a simple struct consisting of 0x1234 in a
uint16_t field to fec0::64. Now, when I run ip-driver to listen on
fec0::64 and use netcat to dump hex, I see the following:
network order is big endian.
On the mote if you use network types ie. nx_uint16_t etc. nx_struct.
then
it will automatically put the bytes in network order and allow you to
reference
the data cells normally. The compiler takes care of accesses.
If I use htons(0x1234) in the tinyos code before sending, I see
"34 12"
If I don't, I see "12 34"
the epic is what kind of byte order?
Now isn't it the convention that network traffic has to be big endian?
Therefore, shouldn't we see "12 34" in netcat's output if I use
htons in
the mote code? I am a little confused since it is actually the
other way
around.
I'm not sure what is going on. Where is netcat picking up the data from?
My question is: Does ip-driver do any kind of byte manipulation or
does
it just create an interface and read from it? Does the blip stack do
htons automatically before sending and receiving data on the mote?
To do that the blip stack would have to somehow know the format of
your data.
Not likely. So I'm going to say no.
To really answer this question you will have to follow the data down
the stack and
see what things look like in memory and how it is organized.
Thanks,
Harsha
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--
Eric B. Decker
Senior (over 50 :-) Researcher
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