RE: [Jsbsim-devel] Matlab-JSBSim Interface

[Jon S. B. <js...@ha...>]

>    Basically, I wrote a Matlab MEX file in C and
> compiled it into a DLL (as MEX files are compiled in a
> Windows environment), which contains multiple
> functions doing the following:
>
>     1. Create a socket given a port number ...
>     2. Delete a socket given the base socket ID ...
>     3. Connect to an already existent socket ...
>     4. Send data to a Socket ...
>     5. Receive data from a socket ...
>
>     Functions 1-4 are working fine as of
> now...ofcourse, there is room for improvement on the
> user friendliness (read..help/usage documentation),
> but I am able to do all those functions, and control
> JSBSim from within matlab.

Good work!

>     Jon, I was thinking...now that its more or less
> clear that this is possible...do you think it would be
> possible for you to consider creating a similar interface as
> FGOutput also on the input side...where you can
> specify in the XML file what data for the simulation
> ...

I have thought about this. So, instead of sending data over a socket like
this:

set fcs/elevator-cmd-norm 0.03
set fcs/rudder-cmd-norm 0.00
...

you could do this:

0.03, 0.00 ...

The spec would be:

<input port="port#">
  <property>fcs/elevator-cmd-norm</property>
  <property>fcs/rudder-cmd-norm</property>
</input>

To avoid the endian issue, I'd still probably do the data transfer using
character strings, unless that's a really bad idea for some reason I'm not
yet aware of. I guess that would require your Matlab/Simulink side to
convert the data, first. It may also then require a precision attribute in
the spec:

<input port="port#">
  <property precision="##.####">fcs/elevator-cmd-norm</property>

>    One more question....does JSBSim work with a fixed
> time step during the simulation...or does it use a
> variable time step solver...?

Fixed timestep. For the moment - given the recent changes to fix the landing
gear jitter problem - that fixed frame rate should be 120 Hz.

>    And...also...is it by anychance possible to drive
> the JSBSim simulation from outside...as in...supply
> the time steps from say..Simulink? (Basically...for
> synchronization between the two systems)

It might be possible to supply a stepping command in the input socket
interface:

step

-or-

step 2

Would that be helpful? I don't think it would be too hard to provide a step
function that would allow a single step to be made or a number of specified
steps.

>    Anyway...now time for driving lessons (ya...my
> Indian license is not valid here in Germany...so need
> to do it all over again :-)!)

I hope it's not too icy there on the roads!

Jon