*
* Hy!
I have some problems in understanding the CRC algorithm within Iris mote.
So I'm using a Matlab code to calculate the CRC but when I compare with the
received CRC I don't see any match beetwen the signals.
My packet format is synch byte || Packet Type ||* ** *Sequence number
||* *Message
address ||* *Message address ||* *Message Type* ||** *Group ID ||* *Packet
size* *||* *Data* || *Data *|| *CRC *|| *CRC * || *synch byte* *.
So, for example I receive at a time instance the following packet:
ans =Val= 126
ans =Val= 66
ans =Val= 125
ans =Val= 94
ans =Val= 0
ans =Val= 4
ans =Val= 125
ans =Val= 93
ans =Val= 4
ans =Val= 94
ans =Val= 28
ans =Val= 11
ans =Val= 0
ans =Val= 186
ans =Val= 10
ans =Val= 126
The red spot is the payload and the next 2 bytes are the CRC! The next code
I use to compare the CRC data received with the one calculated in
matlab(with r value)
File CRC16.m
%**************************************************************************
% This script calculates the 16-bit ITU-T CRC, as described in 7.2.1.9
% IEEE 802.15.4-2006 std. (ZigBee).
%
% Author: Everton Leandro Alves
% Date: 06/19/2008
%
% The generator polynomial is G(x)=x^16+x^12+x^5+1. From the given
% explanation the steps are:
% 1 - Remainder register 'r' is initialized to 0;
% 2 - The message is shifted into the divider (b0 first);
% 3 - Operations are done in the order: a) XORs, b) left shift of r
% register and c) r3 and r10 update.
% 4 - The r register is appended to the message.
%
%**************************************************************************
clear all
clc
msg = [66;125;94;0;4;125;93;4;94;28;11;0];
msg = de2bi(msg,8);
msg = reshape(msg,1,8*length(msg));
r=zeros(1,16); % Remainder register initialization
for c3=1:length(msg)
s1=bitxor(msg(c3),r(1)); % XOR between r0 and the message bit
s2=bitxor(s1,r(12)); % XOR r11
s3=bitxor(s1,r(5)); % XOR r4
r=[r(2:16) s1]; % Left shift of r, and r15 update
r(11)=s2; % r10 update
r(4)=s3; % r3 update
end
msg_FCS=[msg r]; % Message + FCS field
display('Message + FCS field:')
msg_FCS
When I calculate the CRC, I use everything except the two frame synch
bytes, and the two CRC bytes. Does anyone have any clue where I'm going
wrong?
*
*
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