MATLAB: Wireless sensor network code error

Question

I wrote a code to create a WSN with 7 nodes that communicate with each others and where node 7 receive a message from node 1. I have an error that I can't fixed. Help please!

code to initialize node 1:

function node1_init true
ttInitKernel('prioFP');% number of A/D inputs,number of D/A outputs,priority
% init parameters of task
data.a = 0;
data.K = 2;
offset = 0; % time offset is 0
data.exectime = 0.5;
period = 0.0010; % 10 ms, sets period for execution
prio = 1; % basic priority, lower numbers = higher priorities
ttCreatePeriodicTask('sens1_task', offset, period, prio, 'node1code', data);
ttSetPriority(prio, 'sens1_task');

Code node 1:

function [exectime, data] = node1code(seg, data)
switch seg,
case 1,
y = ttAnalogIn(1); % read analog input no 1,
data.a = -data.K * y;
exectime = rand*data.exectime; % we set executing time of read operation
case 2,
ttSendMsg(7, data.a, 80); % send 80 bits to node 3
exectime = 0.5; % we also set delay of this operations
case 3,
exectime = -1; % we are finished, don’t do delay
end

code to nitialize node 7:

function node7_init()
% Init kernel
ttInitKernel('prioFP')
codefcn = 'node7code';
data.u = 0;
prio = 1;
deadline = 10.0;
ttCreateTask('recv_task', deadline, prio, codefcn, data);
ttSetPriority(prio, 'recv_task');
ttAttachNetworkHandler('recv_task')

code node 7:

function [exectime, data] = node7code(seg, data)
switch seg,
case 1,
data.u = ttGetMsg; % read values from node
disp('I got a message');
   exectime = 0.0005;
case 2,
ttAnalogOut(1, data.u);
exectime = -1;
end

I get this error:

%

Answer 1

According to the source code that error is generated when the value to be written is not a scalar double. I suggest you put in some simple code to display the size and class of data.u to see what you are getting instead.