component sstep                 "control spindle speed from an MPG";
pin in  float   rpm             "commanded spindle RPM (float)";
pin in  signed  mpg             "mpg current counts (s32)";
pin in  bit     axis4           "axis4 is selected (bit)";
pin in  bit     x1              "x1 multiplier selected (bit)";
pin in  bit     x10             "x10 multiplier selected (bit)";
pin in  bit     x100            "x100 multiplier selected (bit)";
pin out float   rpm_out         "MPG requested rpm";
pin out bit     fwd             "signal to start spindle CW";
pin out bit     rev             "signal to start spindle CCW";
pin out bit     stop            "signal to stop spindle";
pin out bit     subvert         "MPG has taken control (wired to MPG light)";

param rw signed max_rpm = 1500  "max limit RPM (int)";
param rw signed hold_time =10   "time to hold the button without movng the dial to drop out";

variable signed latched_mpg;
variable signed latched_rpm;
variable signed desired_rpm;
variable float  time = 0.0;

function _;
license "GPL";          // indicates GPL v2 or later
;;

inline int abs(int x){ if(x<0) return -x; return x; }

FUNCTION(_){
    int irpm = (int)rpm;        // we work in int32 here

    if(!axis4 && !subvert){     // if the button is not pressed and we are not already subverting save state
        latched_mpg = mpg;
        latched_rpm = irpm;
        desired_rpm = irpm;
        fwd = rev = stop = 0;
        time = 0;
    }
    // axis 4 selected and button pressed (and held)
    else{
        // has the mpg changed?
        if(mpg!=latched_mpg){
            subvert =  1;       // time to take over
            time = 0;
            int scale=0;
            if(x1)          scale = 1;
            else if(x10)    scale = 10;
            else if(x100)   scale = 100;

            desired_rpm += (mpg - latched_mpg)*scale;
            latched_mpg = mpg;

            // limit to the range
            if(desired_rpm > max_rpm) desired_rpm = max_rpm;
            else if(desired_rpm < -max_rpm) desired_rpm = -max_rpm;
        }
        else if(axis4){             // just riding the button
            time += fperiod;
            if((int)time > hold_time)
                subvert = 0;
        }
    }
    rpm_out = desired_rpm;
}