PS/2 Mouse PID motor control on Linux, code and description

Here is some of my first "proof of concept" code to use a PS/2 mouse to
control two motors with PID.

Description of system
Velleman K8000 I2C I/O board for D/A converters.
Generic roller ball PS/2 mouse all hacked.
Two kids ride-around toy motors.
Mini-ATX (now called ITX) EPIA motherboard.
Mandrake Linux 9.2

The code as follows:

i2cdev.cpp and i2cdev.h, I2C bus interface class
k8000.cpp and k8000.h, k8000 inteface class.
mouse.cpp and mouse.h, PS/2 mouse interface class
mousecode.h, ps/2 mouse protocol codes.

mpwm.cpp, a hacked disaster of test code.

http://64.46.156.80/robot/mousrobot-050412.tar.gz

You will not be able to compile this code "as is" because it is being built
within a much larger code framework, but it shouldn't take much work, and
the mouse, i2c, and velleman classes should require almost nothing. Feel
free to post questions if you want to try it and get stuck.

The one interesting class is the "kbd" class used in mpwm.cpp, on Linux it
wraps code for testing for a key present on the console and reading it. The
important aspect of that code is:

Boolean MFKbd::iskey()
{
        #ifdef Linux

        int n;
        char ch;
        int result = FALSE;

        TRACE_FUNCT("iskey");

        if(m_waiting != EOF)
                result = TRUE;
        else
        {
                m_ionew.c_cc[VMIN]=0;
                tcsetattr(0,TCSANOW,&m_ionew);
                n = read(0,&ch,1);
                m_ionew.c_cc[VMIN]=1;
                tcsetattr(0,TCSANOW,&m_ionew);

                if(n == 1)
                {
                        m_waiting = ch;
                        result = TRUE;
                }
        }

        return result;

        #elif defined( WIN32 )
        return _kbhit();
        #else
        return 0;
        #endif
}

Theory of operation: (in mpwm.cpp)

Encoder is a virtual class to define a set of encoders.
Ps2Encoder is an implementation of Encoder that uses the PS2 mouse interface
class, Mouse.
PIDControl is a class that implements PID control.
In the function: CalcPID:
PID stands for: Proportional, Integral, Derivitive
error is the difference between target and actual.
Propotional comes from the current error times a "gain" value.
Integral comes from an accumulated error times a "gain" value.
Derivitive comes from the difference between the previous error and current
error times a "gain" value.

 
Loop operation:

Check if a key is hit, if so, read it and act on it. (Allows to play with
the various gains and speed.)
get current time of day.
Update the encoder values.
Calculate elapsed time from start
Get the current encoder values.
Scale them for elapsed time.
calculate the PID.
If a second has passed, print a report. (Test code, will not be there
later.)
Calculate the proper values for the motor control.
Send them out if they are different than the last time.
Save the current time as start.
loop.