Diff: reckoner.h

Revision:

12:835a4d24ae3b

Child:

13:bba5b3abd13f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/reckoner.h	Sun Feb 23 22:23:34 2014 +0000
@@ -0,0 +1,46 @@
+// 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;
\ No newline at end of file