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<H1><A NAME="SECTION00630000000000000000">
Developing the <TT>user_controller.c</TT> File</A>
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<P>
Last, and must importantly, we need to write the piece of code that
will do the ``heavy'' work. That is, this is the file that contains
our controller algorithm - for example, this file would define a PID
controller, or an <IMG
WIDTH="37" HEIGHT="37" ALIGN="MIDDLE" BORDER="0"
SRC="img71.png"
ALT="$H_\infty$"> controller, or a real time model, to name
a few. For our meager task at hand, we do not crave such lofty
algorithms. In fact, our algorithm is so simple that it can be shown
in its entirety here:
<P><PRE>
#include "main.h"
int
control_init(void)
{
return(RTIC_SUCCESS);
}
void
control_run(void)
{
int i;
float tmp;
for (i=0; i<NUM_CONTROL_INPUTS; i++)
{
RETURN_VAL(i,GET_SENSOR(i));
}
for (i=0; i<NUM_CONTROL_OUTPUTS; i++)
{
tmp = GET_SCALAR_PARAMETER(i);
SET_VOLTAGE(i,tmp);
RETURN_VAL(NUM_CONTROL_INPUTS+i,tmp);
}
}
int
control_stop(void)
{
return(RTIC_SUCCESS);
}
</PRE>
<P>
We begin by including ``main.h''. This must be included every single
time. Then, we define our three functions as prescribed in a previous
chapter: <TT>control_init()</TT>, <TT>control_run()</TT>, and <TT>control_stop()</TT>. In our case, we do not need to initialize any states
as would be necessary in a PID or State Space type controller, so we
leave our <TT>control_init()</TT> function blank. We also don't have
any shutdown restrictions, therefore the <TT>control_stop()</TT>
function is also left blank.
<P>
The story is different for the <TT>control_run()</TT> function. This
function has two main loops. The first loop reads in the sensor
readings via the <TT>GET_SENSOR</TT> macro, and returns these values in
the first five columns of our data output. The second loop first
reads in the value set by the user in the spin buttons, assign it to a
temporary variable <TT>tmp</TT>, sets the voltage at the D/A outputs to
the value set in <TT>tmp</TT>, and appends these values to the last five
columns of the data output.
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<ADDRESS>
Michael Barabanov
2001-06-19
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