File content as of revision 12:835a4d24ae3b:

// Robot configuration:

// General purpose code:

class Reckoner
{
    public:
    
    Reckoner();
    
    // Together, cos and sin form a vector with a magnitude close to 2^30 that indicates
    // the current position of the robot.  By definition, when the reckoning starts,
    // sin is 0 and cos is 2^30.
    // cos corresponds to the x component of the orientation vector.
    // sin corresponds to the y component of the orientation vector.
    int32_t cos, sin;
    
    // Together, x and y are a vector that points from the starting point to the
    // robot's current position.
    // Units:
    // * If the units are too big, precision is lost.
    // * If they are too small, the integers wil overflow.
    // * For convenience, they should be a power of 2 off from Df (Distance robot moves
    //   forward per encoder tick), so we can just write x += cos >> some_constant.
    // * Worst case for overflow: our encoders give us a Df of 0.25mm and our robot moves
    //   5m away from the starting point.  Therefore, x and y might need to hold a value
    //   20000 or -20000 without overflowing.
    //   Overflow condition:              x = (1<<31)
    //                20000*Df < max_dist_x = (1<<31) * U
    //                                U > Df * (20000) / (1<<31) = Df / (1<<16)
    // * Therefore the units we choose for x are Df / (1<<16).
    // * If we wrote x += cos it would mean the units are Df / (1<<30).
    //   Instead, we write x += cos >> 14 so the units are correct.
    int32_t x, y;

    void handleTickLeftForward();
    void handleTickLeftBackward();
    void handleTickRightForward();
    void handleTickRightBackward();
    void handleForward();
    void handleBackward();
    void handleRight();
    void handleLeft();
};

extern Reckoner reckoner;