Separate PW Limit calculation into own function and optimise. Add unit tests for this

speeduino/speeduino.h

@@ -20,6 +20,7 @@ void loop(void);
 uint16_t PW(int REQ_FUEL, byte VE, long MAP, uint16_t corrections, int injOpen);
 byte getVE1(void);
 byte getAdvance1(void);
+uint16_t calculatePWLimit();
 void calculateStaging(uint32_t);
 void calculateIgnitionAngles(int dwellAngle);
 void checkLaunchAndFlatShift();

speeduino/speeduino.ino

@@ -467,14 +467,7 @@ void loop(void)
       #endif
       
       //Check that the duty cycle of the chosen pulsewidth isn't too high.
-      uint32_t pwLimit = percentage(configPage2.dutyLim, revolutionTime); //The pulsewidth limit is determined to be the duty cycle limit (Eg 85%) by the total time it takes to perform 1 revolution
-      //Handle multiple squirts per rev
-      if (configPage2.strokes == FOUR_STROKE) { pwLimit = pwLimit * 2; }
-      // This requires 32-bit division, which is very slow on Mega 2560.
-      // So only divide if necessary - nSquirts is often only 1.
-      if (currentStatus.nSquirts!=1) {
-        pwLimit = pwLimit / currentStatus.nSquirts;
-      }
+      uint16_t pwLimit = calculatePWLimit();
       //Apply the pwLimit if staging is disabled and engine is not cranking
       if( (!BIT_CHECK(currentStatus.engine, BIT_ENGINE_CRANK)) && (configPage10.stagingEnabled == false) ) { if (currentStatus.PW1 > pwLimit) { currentStatus.PW1 = pwLimit; } }
 
@@ -1440,6 +1433,36 @@ void calculateIgnitionAngles(int dwellAngle)
   }
 }
 
+uint16_t calculatePWLimit()
+{
+  uint32_t tempLimit = percentage(configPage2.dutyLim, revolutionTime); //The pulsewidth limit is determined to be the duty cycle limit (Eg 85%) by the total time it takes to perform 1 revolution
+  //Handle multiple squirts per rev
+  if (configPage2.strokes == FOUR_STROKE) { tempLimit = tempLimit * 2; }
+  //Optimise for power of two divisions where possible
+  switch(currentStatus.nSquirts)
+  {
+    case 1:
+      //No action needed
+      break;
+    case 2:
+      tempLimit = tempLimit / 2;
+      break;
+    case 4:
+      tempLimit = tempLimit / 4;
+      break;
+    case 8:
+      tempLimit = tempLimit / 8;
+      break;
+    default:
+      //Non-PoT squirts value. Perform (slow) uint32_t division
+      tempLimit = tempLimit / currentStatus.nSquirts;
+      break;
+  }
+  if(tempLimit > UINT16_MAX) { tempLimit = UINT16_MAX; }
+
+  return tempLimit;
+}
+
 void calculateStaging(uint32_t pwLimit)
 {
   //Calculate staging pulsewidths if used

test/test_fuel/test_PW.cpp

@@ -14,6 +14,8 @@ void testPW(void)
   RUN_TEST(test_PW_Large_Correction);
   RUN_TEST(test_PW_Very_Large_Correction);
   RUN_TEST(test_PW_4Cyl_PW0);
+  RUN_TEST(test_PW_Limit_Long_Revolution);
+  RUN_TEST(test_PW_Limit_90pct);
 }
 
 int16_t REQ_FUEL;
@@ -142,3 +144,24 @@ void test_PW_4Cyl_PW0(void)
   TEST_ASSERT_EQUAL(0, currentStatus.PW3);
   TEST_ASSERT_EQUAL(0, currentStatus.PW4);
 }
+
+//Tests the PW Limit calculation for a normal scenario
+void test_PW_Limit_90pct(void)
+{
+  revolutionTime = 10000UL; //6000 rpm
+  configPage2.dutyLim = 90;
+
+  //Duty limit of 90% for 10,000uS should give 9,000
+  TEST_ASSERT_EQUAL(9000, calculatePWLimit());
+}
+
+//Tests the PW Limit calculation when the revolution time is greater than the max UINT16 value
+//Occurs at approx. 915rpm
+void test_PW_Limit_Long_Revolution(void)
+{
+  revolutionTime = 100000UL; //600 rpm, below 915rpm cutover point
+  configPage2.dutyLim = 90;
+
+  //Duty limit of 90% for 100,000uS should give 90,000, but as this would overflow the PW value, this should default to UINT16 Max
+  TEST_ASSERT_EQUAL(UINT16_MAX, calculatePWLimit());
+}

test/test_fuel/test_PW.h

@@ -7,3 +7,5 @@ void test_PW_ALL_Multiply(void);
 void test_PW_Large_Correction();
 void test_PW_Very_Large_Correction();
 void test_PW_4Cyl_PW0(void);
+void test_PW_Limit_90pct(void);
+void test_PW_Limit_Long_Revolution(void);