Index: firmware/App/Controllers/DialInFlow.c
===================================================================
diff -u -rd91a24c730aeb5cd7e3eba9ef4eca78e442911f8 -r5e77f78c5dee9dfb441bd5d2053f7f4ac50dc619
--- firmware/App/Controllers/DialInFlow.c	(.../DialInFlow.c)	(revision d91a24c730aeb5cd7e3eba9ef4eca78e442911f8)
+++ firmware/App/Controllers/DialInFlow.c	(.../DialInFlow.c)	(revision 5e77f78c5dee9dfb441bd5d2053f7f4ac50dc619)
@@ -52,7 +52,8 @@
 
 #define DIP_HOME_RATE                        100             ///< target pump speed (in estimate mL/min) for homing.
 #define DIP_HOME_TIMEOUT_MS                  10000           ///< maximum time allowed for homing to complete (in ms).
-#define DIP_SPEED_CALC_INTERVAL              ( MS_PER_SECOND / TASK_PRIORITY_INTERVAL )  ///< interval (ms/task time) at which the dialysate inlet pump speed is calculated.
+#define DIP_SPEED_CALC_INTERVAL              ( 40 / TASK_PRIORITY_INTERVAL )  ///< interval (ms/task time) at which the dialysate inlet pump speed is calculated.
+#define DIP_SPEED_CALC_BUFFER__LEN           25              ///< number of hall sensor counts kept in buffer to hold last 1 second of count data.
 #define DIP_HALL_EDGE_COUNTS_PER_REV         48              ///< number of hall sensor edge counts per motor revolution.
 
 #define DIP_MAX_FLOW_VS_SPEED_DIFF_ML_MIN    50.0            ///< maximum difference between measured flow and flow implied by measured motor speed.
@@ -147,7 +148,8 @@
 static BOOL dipStopAtHomePosition = FALSE;                                          ///< stop dialysate inlet pump at next home position
 static U32 dipHomeStartTime = 0;                                                    ///< when did dialysate inlet pump home command begin? (in ms)
 
-static U16 dipLastMotorHallSensorCount = 0;                                         ///< last hall sensor count for the dialysate inlet pump motor
+static U16 dipLastMotorHallSensorCounts[ DIP_SPEED_CALC_BUFFER__LEN ];              ///< last hall sensor count for the blood pump motor
+static U32 dipMotorSpeedCalcIdx = 0;                                                ///< index into 1 second buffer of motor speed hall sensor counts
 static MOTOR_DIR_T dipMotorDirectionFromHallSensors = MOTOR_DIR_FORWARD;            ///< pump direction according to hall sensor count
 static U32 dipMotorSpeedCalcTimerCtr = 0;                                           ///< counter determines interval for calculating dialysate inlet pump motor speed from hall sensor count.
 
@@ -196,15 +198,22 @@
  * @return none
  *************************************************************************/
 void initDialInFlow( void )
-{
-    dipLastMotorHallSensorCount = getFPGADialInPumpHallSensorCount();
+{
+    U32 i;
 
     stopDialInPump();
     setDialInPumpDirection( MOTOR_DIR_FORWARD );
 
     // zero rolling flow average buffer
     resetDialInFlowMovingAverage();
 
+    // zero motor hall sensors counts buffer
+    dipMotorSpeedCalcIdx = 0;
+    for ( i = 0; i < DIP_SPEED_CALC_BUFFER__LEN; i++ )
+    {
+        dipLastMotorHallSensorCounts[ i ] = 0;
+    }
+
     // initialize dialysate inlet flow PI controller
     initializePIController( PI_CONTROLLER_ID_DIALYSATE_FLOW, MIN_DIAL_IN_PUMP_PWM_DUTY_CYCLE,
                             DIP_P_COEFFICIENT, DIP_I_COEFFICIENT,
@@ -874,7 +883,8 @@
     if ( ++dipMotorSpeedCalcTimerCtr >= DIP_SPEED_CALC_INTERVAL )
     {
         U16 dipMotorHallSensorCount = getFPGADialInPumpHallSensorCount();
-        U16 incDelta = ( dipMotorHallSensorCount >= dipLastMotorHallSensorCount ? dipMotorHallSensorCount - dipLastMotorHallSensorCount : ( HEX_64_K - dipLastMotorHallSensorCount ) + dipMotorHallSensorCount );
+        U32 nextIdx = INC_WRAP( dipMotorSpeedCalcIdx, 0, DIP_SPEED_CALC_BUFFER__LEN - 1 );
+        U16 incDelta = ( dipMotorHallSensorCount >= dipLastMotorHallSensorCounts[ nextIdx ] ? dipMotorHallSensorCount - dipLastMotorHallSensorCounts[ nextIdx ] : ( HEX_64_K - dipLastMotorHallSensorCounts[ nextIdx ] ) + dipMotorHallSensorCount );
         U16 decDelta = HEX_64_K - incDelta;
         U16 delta;
 
@@ -893,7 +903,8 @@
         }
 
         // update last count for next time
-        dipLastMotorHallSensorCount = dipMotorHallSensorCount;
+        dipLastMotorHallSensorCounts[ nextIdx ] = dipMotorHallSensorCount;
+        dipMotorSpeedCalcIdx = nextIdx;
         dipMotorSpeedCalcTimerCtr = 0;
     }
 }