I am new in OMNeT++. I am doing a simple simulation where a client sends some packets to a server. I want, for instance, store the timestamp of the first packet sent, and later, I want store the timestamp of the tenth package sent. I would want to be able to store those two timestamps in two variables, timestamp_of_first_packet and timestamp_of_last_packet, kind of like
packets_sent = 1
cPacket* testPacket = new cPacket();
double timestamp_of_first_packet = testPacket->getTimestamp().dbl();
packets_sent++;
...
double timestamp_of_last_packet = testPacket->getTimestamp().dbl();
The aim is to calculate a time interval between the two packets, with this formula:
double time_interval = timestamp_of_last_packet - timestamp_of_first_packet;
I know that this method is wrong, because both variables store the same value.
How I can store both timestamps correctly? Thanks in advance.
You can get the current simulation time by calling simTime(). If you want some time to pass in your simulation, have your module schedule an event to itself (using scheduleAt). Remember your module is written in C++, so you can use all its features (like member variables) to write clean code.
Related
I am trying to control a robot using a template-based controller class written in c++. Essentially I have a UDP connection setup with the robot to receive the state of the robot and send new torque commands to the robot. I receive new observations at a higher frequency (say 2000Hz) and my controller takes about 1ms (1000Hz) to calculate new torque commands to send to the robot. The problem I am facing is that I don't want my main code to wait to send the old torque commands while my controller is still calculating new commands to send. From what I understand I can use Ubuntu with RT-Linux kernel, multi-thread the code so that my getTorques() method runs in a different thread, set priorities for the process, and use mutexes and locks to avoid data race between the 2 threads, but I was hoping to learn what the best strategies to write hard-realtime code for such a problem are.
// main.cpp
#include "CONTROLLER.h"
#include "llapi.h"
void main{
...
CONTROLLERclass obj;
...
double new_observation;
double u;
...
while(communicating){
get_newObs(new_observation); // Get new state of the robot (2000Hz)
obj.getTorques(new_observation, u); // Takes about 1ms to calculate new torques
send_newCommands(u); // Send the new torque commands to the robot
}
...
}
Thanks in advance!
Okay, so first of all, it sounds to me like you need to deal with the fact that you receive input at 2 KHz, but can only compute results at about 1 KHz.
Based on that, you're apparently going to have to discard roughly half the inputs, or else somehow (in a way that makes sense for your application) quickly combine the inputs that have arrived since the last time you processed the inputs.
But as the code is structured right now, you're going to fetch and process older and older inputs, so even though you're producing outputs at ~1 KHz, those outputs are constantly being based on older and older data.
For the moment, let's assume you want to receive inputs as fast as you can, and when you're ready to do so, you process the most recent input you've received, produce an output based on that input, and repeat.
In that case, you'd probably end up with something on this general order (using C++ threads and atomics for the moment):
std::atomic<double> new_observation;
std::thread receiver = [&] {
double d;
get_newObs(d);
new_observation = d;
};
std::thread sender = [&] {
auto input = new_observation;
auto u = get_torques(input);
send_newCommands(u);
};
I've assumed that you'll always receive input faster than you can consume it, so the processing thread can always process whatever input is waiting, without receiving anything to indicate that the input has been updated since it was last processed. If that's wrong, things get a little more complex, but I'm not going to try to deal with that right now, since it sounds like it's unnecessary.
As far as the code itself goes, the only thing that may not be obvious is that instead of passing a reference to new_input to either of the existing functions, I've read new_input into variable local to the thread, then passed a reference to that.
I am currently working on implementing a simple oscilloscope in C++, which is receiving data via UDP. First, I have implemented a function to generate a sine wave (up to 10 kHz) with 30 kSps, which is transferring this data via UDP locally. On the other side, there is a (QWT) plot. The UDP client is running in a thread appending the received values (and delete the first one) to a Qlist, while the plot is updated every 30 ms via a timer.
The question is now, how can I implement a simple oscilloscope which plots the signal with its original frequency, independent of the number of samples it receives (implement a time base)? Could you give me some general ideas? Thanks in advance.
Solution:
The solution is to copy (every time the plot is updated, here 30 ms) the Qlist of the received items to a temporary variable and delete the Qlist. Then, create a time vector for this temporary variable. The time vector is created via this function:
QVector<double> make_vector(double start, double end, double size)
{
QVector<double> vec;
double step = abs((abs(start) - abs(end)))/size;
while (start <= end)
{
vec.push_back(start);
start += step;
}
return vec;
}
For example, to scale the value to 1 second I am calling this function like: make_vector(-1.0, 0.0, temporary variable.size()).
By this procedure, the plot is independent of the number of sample received. You only have to make sure that you receive enough values in your time period (here 30 ms).
I am working on a project in which I am controlling a quadcopter with an android phone. I have noticed that the using the DroneListener to listen for ATTITUDE_UPDATED messages is not updating the yaw nearly as fast enough as I need it to. I would like to get the quadcopter’s yaw updated frequently, in (more or less) real time, such as how the Mission Planner application does when you plug your quadcopter in via usb.
I have tried using msg_request_data_stream (that is essentially what Mission Planner uses, but in C#) to request various data streams from the drone, but it has not worked. My assumption is that such the response to this request (i.e., the stream) would be received by any registered MavlinkObservers, however the custom MavlinkObserver that I have added to my drone has not had its onMavlinkMessageReceived(…) method called a single time. It has not even received heartbeat messages, which should (based on my understanding) be coming reqularly and frequently.
Is there any help that you could offer? Is there any better way to get the quadcopter’s yaw than waiting for the DroneListener to be notified of events? I know that it should be possible with Mavlink (MissionPlanner does it), but I haven’t been having any success with Mavlink messages or with a MavlinkObserver.
Here is my code for requesting a data stream:
msg_request_data_stream message = new msg_request_data_stream();
//not sure how doubles cast to byte, so I cast it to an int first (the value is
//always going to be an int anyway, getValue just returns doubles for parameters by default)
message.target_system = (byte)((int)params.getParameter("SYSID_THISMAV").getValue());
message.req_message_rate = (short)1;
message.req_stream_id = (byte)0;
message.start_stop = (byte)1;
//wrap the message and send it!
ExperimentalApi.sendMavlinkMessage(this, new MavlinkMessageWrapper(message));
I need help making a gnuradio OOT module. I am actually trying to extending one code.
I am trying to make 2 TX 1Rx tagged stream block (OOT). For 1Tx 1Rx, it
is working fine. I am trying to extend it. Now the problem is, I am not
being able to configure the send() function. With this code, one transmitter transmits, but other does not work. The subdev specification and frequency and other parameters are allocated correctly. I checked.
If I try make test, it does not show any problem. I checked the every
port of my USRP X310, it is working fine.
Here's the code. I putting a short part which deals with the send and receive buffer.
void
usrp_echotimer_cc_impl::send()
{
// Data to USRP
num_tx_samps = d_tx_stream->send(d_in_send1, total_num_samps,
d_metadata_tx, total_num_samps/(float)d_samp_rate+d_timeout_tx);
num_tx_samps = d_tx_stream->send(d_in_send0, total_num_samps,
d_metadata_tx, total_num_samps/(float)d_samp_rate+d_timeout_tx);
}
int
usrp_echotimer_cc_impl::work (int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
gr_complex *in0 = (gr_complex *) input_items[0];
gr_complex *in1 = (gr_complex *) input_items[1];
gr_complex *out = (gr_complex *) output_items[0];
// Set output items on packet length
noutput_items = ninput_items[0]=ninput_items[1];
// Resize output buffer
if(d_out_buffer.size()!=noutput_items)
d_out_buffer.resize(noutput_items);
// Send thread
d_in_send0 = in0;
d_in_send1 = in1;
d_noutput_items_send = noutput_items;
d_thread_send =
gr::thread::thread(boost::bind(&usrp_echotimer_cc_impl::send, this));
// Receive thread
d_out_recv = &d_out_buffer[0];
d_noutput_items_recv = noutput_items;
d_thread_recv =
gr::thread::thread(boost::bind(&usrp_echotimer_cc_impl::receive, this));
My system config is X310, daughterboard SBX-120 and I am using UHD-3.9. I checked the subdev specification, gain and frequency assignment. Those
are fine.
For completeness:
This has been asked yesterday on the GNU Radio mailing list; Sanjoy has already gotten two responses:
Martin Braun wrote:
Sorry, Sanjoy,
we'll need some more information before we can give you better
feedback. It's not clear exactly what you're trying to achieve, and
what exactly is failing.
Perhaps this helps getting started:
http://gnuradio.org/redmine/projects/gnuradio/wiki/ReportingErrors
Cheers, Martin
And my answer is a bit longish, but it's available here. In excerpts:
Hi Sanjoy,
I am trying to make 2 TX 1Rx tagged stream block(OOT). For 1Tx 1Rx, it was working fine. I am trying to extend it. Now the problem is, I
am not being able to configure the send() function.
Is there a
particular reason you're creating your own block? Is there a feature
missing on the USRP sink and source that come with gr-uhd?
...
your send() function looks a bit strange; what you're doing is
transmitting two things on a single channel after each other. Also,
what you should be doing (from a programming style point of view) is
pass the buffers you want to send as references or something, but not
save them to class properties and then call send(). To send two
buffers to two different channels, you will need to use a vector
containing the two buffers -- have a look at rx_multi_samples; that of
course recv()s rather than sends(), but the semantics are the same.
...
noutput_items is given to you to let your work now how much it may produce, that's why it's a parameter.
...
There's no reason GNU Radio couldn't already call your work function again while usrp_echotimer_cc_impl::send() hasn't even started to transmit samples. Then, your d_send variables will be overwritten.
...
Since a single X310 is inherently coherent and has the same time, you can simply use a USRP sink and a source, use set_start_time(...) on both with the same time spec, and have your flow graph consume and produce samples in different threads, coherently.
I create a round of processes in erlang and wish to measure the time that it took for the first message to pass throigh the network and the entire message series, each time the first node gets the message back it sends another one.
right now in the first node i have the following code:
receive
stop->
io:format("all processes stopped!~n"),
true;
start->
statistics(runtime),
Son!{number, 1},
msg(PID, Son, M, 1);
{_, M} ->
{Time1, _} = statistics(runtime),
io:format("The last message has arrived after ~p! ~n",[Time1*1000]),
Son!stop;
of course i start the statistics when sending the first message.
as you can see i use the Time_Since_Last_Call for the first message loop and wish to use the Total_Run_Time for the entire run, the problem is that Total_Run_Time is accumulative since i start the statistics for the first time.
The second thought i had in mind is using another process with 2 receive loops getting the times for each one adding them and printing but i'm sure that erlang can do better than this.
i guess the best method to solve this is somehow flush the Total_Run_Time, but i couldn't find how this could be done. any ideas how this can be tackled?
One way to measure round-trip times would be to send a timestamp along with each message. When the first node receives the message, it can then measure the round-trip time, calculating Total_Run_Time - Timestamp.
To calculate the total run time, I would memorize the first timestamp in the process state (or dictionary), and calculate the total run time when stopping the test.
Besides, given that you mention the network, are you sure that the CPU time (which is what statistics(runtime) calculates is what you're after? Perhaps, wall clock time would be more appropriate.