Improved performance and fixed point algorithm

Author: Dlloydev

QuickPID.cpp

@@ -66,15 +66,11 @@ bool QuickPID::Compute()
     error = *mySetpoint - input;
 
     /*Working error, Proportional on Measurement and Remaining PID output*/
-    if (!pOnE) {
-      outputSum += (ki * error);
-      outputSum -= (kpd * dInput);
-    }
+    if (!pOnE) outputSum += FX_MUL(FL_FX(ki) , error) - FX_MUL(FL_FX(kpd), dInput);
+
     /*Working error, Proportional on Error and remaining PID output*/
-    if (pOnE) {
-      outputSum += (kpi * error);
-      outputSum -= (kd * dInput);
-    }
+    if (pOnE) outputSum += FX_MUL(FL_FX(kpi) , error) - FX_MUL(FL_FX(kd), dInput);
+
     if (outputSum > outMax) outputSum = outMax;
     if (outputSum < outMin) outputSum = outMin;
     *myOutput = outputSum;
@@ -232,19 +228,19 @@ bool QuickPID::GetDirection() {
 int QuickPID::analogReadFast(int ADCpin) {
 #if defined(__AVR_ATmega328P__)
   byte ADCregOriginal = ADCSRA;
-  ADCSRA = (ADCSRA & B11111000) | 6; //64 prescaler
+  ADCSRA = (ADCSRA & B11111000) | 5; //32 prescaler
   int adc = analogRead(ADCpin);
   ADCSRA = ADCregOriginal;
   return adc;
 #elif defined(__AVR_ATtiny_Zero_One__) || defined(__AVR_ATmega_Zero__)
   byte ADCregOriginal = ADC0_CTRLC;
-  ADC0_CTRLC = 0x55; //reduced cap, Vdd ref, 64 prescaler
+  ADC0_CTRLC = 0x54; //reduced cap, Vdd ref, 32 prescaler
   int adc = analogRead(ADCpin);
   ADC0_CTRLC = ADCregOriginal;
   return adc;
 #elif defined(__AVR_DA__)
   byte ADCregOriginal = ADC0.CTRLC;
-  ADC0.CTRLC = ADC_PRESC_DIV64_gc; //64 prescaler
+  ADC0.CTRLC = ADC_PRESC_DIV32_gc; //32 prescaler
   int adc = analogRead(ADCpin);
   ADC0.CTRLC = ADCregOriginal;
   return adc;

QuickPID.h

@@ -14,6 +14,9 @@ class QuickPID
 #define P_ON_M  0
 #define P_ON_E  1
 
+#define FL_FX(a) (int32_t)(a*256.0)  // float to fixed point
+#define FX_MUL(a,b) ((a*b)>>8)       // fixed point multiply
+
 
     // commonly used functions ************************************************************************************
 

README.md

@@ -3,7 +3,8 @@
 This API (version 2.02) follows the [ArduinoPID](https://github.com/br3ttb/Arduino-PID-Library) library, however there have been some significant updates as follows:
 
 - Library named as **QuickPID** and can run concurrently with Arduino **PID**
-- Reorganized and more efficient PID algorithms
+- Quicker fixed point math in compute function
+- Reorganized and more efficient PID algorithm
 - micros() timing resolution
 - Faster analog read function
 - `GetError()`function added for diagnostics
@@ -12,10 +13,10 @@ This API (version 2.02) follows the [ArduinoPID](https://github.com/br3ttb/Ardui
 
 | Compute                              | Kp   | Ki   | Kd   | Step Time (µS) |
 | :----------------------------------- | ---- | ---- | ---- | -------------- |
-| QuickPID                             | 2.0  | 15.0 | 0.05 | 72             |
+| QuickPID                             | 2.0  | 15.0 | 0.05 | 68             |
 | Arduino PID                          | 2.0  | 15.0 | 0.05 | 104            |
 | **analogRead, Compute, analogWrite** |      |      |      |                |
-| QuickPID                             | 2.0  | 5.0  | 0.2  | 132            |
+| QuickPID                             | 2.0  | 5.0  | 0.2  | 96             |
 | Arduino PID                          | 2.0  | 5.0  | 0.2  | 224            |
 
 #### Self Test Example (RC Filter): P_ON_M

examples/QuickPID_Self_Test/QuickPID_Self_Test.ino

@@ -59,7 +59,7 @@ void loop()
   after = micros();
   analogWrite(PIN_OUTPUT, Output);
 
-  delay(20);
+  delay(40);
   cnt++;
   if (cnt == 100) {
     analogWrite(PIN_OUTPUT, 0);