一条随手的Arduino sketch优化 以Examples-02.Digital-Debounce为例

 1 const int buttonPin = 2;
 2 const int ledPin = 13;
 3
 4 int ledState = HIGH;
 5 int buttonState;
 6 int lastButtonState = LOW;
 7
 8 unsigned long lastDebounceTime = 0;
 9 unsigned long debounceDelay = 50;
10
11 void setup() {
12   pinMode(buttonPin, INPUT);
13   pinMode(ledPin, OUTPUT);
14   digitalWrite(ledPin, ledState);
15 }
16
17 void loop() {
18   int reading = digitalRead(buttonPin);
19   if (reading != lastButtonState) {
20     lastDebounceTime = millis();
21   }
22   if ((millis() - lastDebounceTime) > debounceDelay) {
23     if (reading != buttonState) {
24       buttonState = reading;
25       if (buttonState == HIGH) {
26         ledState = !ledState;
27       }
28     }
29   }
30   digitalWrite(ledPin, ledState);
31   lastButtonState = reading;
32 }

原文的代码 暂时去掉注释，便于显示重点。

编译结果：

Sketch uses 1116 bytes (3%) of program storage space. Maximum is 30720 bytes.
Global variables use 19 bytes (0%) of dynamic memory, leaving 2029 bytes for local variables. Maximum is 2048 bytes.

优化手段1：选用够用的数据类型，这里面的int对象，都是小于255的，可以换成byte：

const byte buttonPin = 2;
const byte ledPin    = 13;
byte ledState = HIGH;
byte buttonState;
byte lastButtonState = LOW;

unsigned long lastDebounceTime = 0;
unsigned long debounceDelay    = 50;

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(ledPin,    OUTPUT);
  digitalWrite(ledPin, ledState);
}

void loop() {
  byte reading = digitalRead(buttonPin);
  if (reading != lastButtonState) {
    lastDebounceTime = millis();
  }
  if ((millis() - lastDebounceTime) > debounceDelay) {
    if (reading != buttonState) {
      buttonState = reading;
      if (buttonState == HIGH) {
        ledState = !ledState;
      }
    }
  }
  digitalWrite(ledPin, ledState);
  lastButtonState = reading;
}

　　

编译结果：

Sketch uses 1074 bytes (3%) of program storage space. Maximum is 30720 bytes.
Global variables use 17 bytes (0%) of dynamic memory, leaving 2031 bytes for local variables. Maximum is 2048 bytes.

效果：

程序空间减少42字节；SRAM减少2字节。

继续淦：

里面有一个函数在相近的位置，用了两遍，且貌似挺复杂的，就是：millis();

将其合二为一，但是又要增加一个全局变量，试试效果：

const byte buttonPin = 2;
const byte ledPin    = 13;
byte ledState = HIGH;
byte buttonState;
byte lastButtonState = LOW;
unsigned long lastDebounceTime = 0;
unsigned long debounceDelay    = 50;
unsigned long ml = 0;

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(ledPin,    OUTPUT);
  digitalWrite(ledPin, ledState);
}
void loop() {
  byte reading = digitalRead(buttonPin);
  ml = millis();
  if (reading != lastButtonState) {
    lastDebounceTime = ml;
  }
  if ((ml - lastDebounceTime) > debounceDelay) {
    if (reading != buttonState) {
      buttonState = reading;
      if (buttonState == HIGH) {
        ledState = !ledState;
      }
    }
  }
  digitalWrite(ledPin, ledState);
  lastButtonState = reading;
}

　　编译结果：

Sketch uses 1052 bytes (3%) of program storage space. Maximum is 30720 bytes.
Global variables use 17 bytes (0%) of dynamic memory, leaving 2031 bytes for local variables. Maximum is 2048 bytes.

又干掉22字节的程序空间，SRAM竟然没变？

(1166-1052)/1166 = 104/1166 = 9.8%

将近10%的优化成果，这还没使用骨灰级的寄存器大法来优化pinMode和digitalRead/Write。

后续再试：const byte debounceDelay    = 50; 结果还是1052、17，看来是编译器自动将其优化了。