Fixed a number of bugs caused by using abs() on floats and long ints. Added support for selectively inverting bits of the stepping port. Debugged, optimized and cleaned up timing code for the step-pulses.

main.c

@@ -33,12 +33,14 @@
 int main(void)
 {
   beginSerial(BAUD_RATE);
-  st_init();
+  st_init(); // initialize the stepper subsystem
   mc_init(); // initialize motion control subsystem
   spindle_init(); // initialize spindle controller
   gc_init(); // initialize gcode-parser
   sp_init(); // initialize the serial protocol
   
+  st_start(); // start the stepper subsystem
+  
   for(;;){
     sleep_mode();
     sp_process(); // process the serial protocol