presumably fixed the feed rate computation

serial_protocol.h

@@ -25,7 +25,12 @@
 // A character to acknowledge that the execution has started
 #define EXECUTION_MARKER '~'
 
+// Initialize the serial protocol
 void sp_init();
+// Called by motion control just before the motion starts
+void sp_send_execution_marker();
+// Read command lines from the serial port and execute them as they
+// come in. Blocks until the serial buffer is emptied. 
 void sp_process();
 
 #endif