Running counters using S-functions
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Hello,
I am designing an autopilot waypoint tracking system. I have a list of waypoints. The autopilot is given the first as a reference waypoint and when the aircraft gets a distance D close to the waypoint, I want the reference to change to the next waypoint. I did this by having a flag based on whether the aircraft is D distance close to the waypoint or not (1 if it is and 0 if it is not). The flag increments a counter which keeps track of which waypoint is currently the reference.
I learned (the hard way) that variables passed to workspace during the simulation are not available until after the simulation and the only way to have a running counter would be through S-functions.
The question I have is: How can I (can I even?) build a simple S-function that increments a fixed counter based on a flag input and then outputs the value of the fixed counter (which will be used to determine the current waypoint)? I've been using the S-function builder but I'm not sure how to reference a static/global/base-workspace variable (I'm not too familiar with C either).
Any help would be tremendously appreciated.
~ IH
采纳的回答
Kaustubha Govind
2011-6-8
If this is all you want your S-function to do, then you can simply implement your own subsystem (using a unit delay block to store the counter's state) or use an Embedded MATLAB Fcn block containing code to the effect of:
function y = fcn(u)
%#codegen
persistent counter;
if isempty(counter)
counter = 0; %initialize
end
if (u == 1) %implement this condition as per your requirement
counter = counter + 1;
end
y = counter;
Is there a reason you chose to use a C-MEX S-function instead? (By the way, I would recommend Level-2 MATLAB file S-functions or Embedded MATLAB Functions if you are not comfortable with C/C++ and need to perform simple enough operations)
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2011-6-8
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