[英]Global variable doesn't update prior to next loop
我正在嘗試在 C++ 中為我的 ESP32 構建轉速計。 當我取消注釋Serial.printf("outside rev: %d \n", rev);
在條件之外它可以工作,但是當我評論它時,我得到的值比它們應該的值大幾個數量級(沒有 700 轉,有 7 轉)。 我最好的猜測是 print 語句正在減慢loop()
的速度,剛好足以讓incrementRevolutions()
在下一個循環之前將全局變量passedMagnet
從 true 切換為 false。 這是有道理的,因為延遲更新 passMagnet 將允許newRevCount++;
被觸發多次。 但鑒於競態條件的時間敏感性,這顯然是我無法使用打印語句或逐步調試來調試的。
bool passedMagnet = true;
int incrementRevolutions(int runningRevCount, bool passingMagnet)
{
// Serial.printf("passedMagnet: %d , passingMagnet %d , runningRevCount: %d \n", passedMagnet, passingMagnet, runningRevCount);
int newRevCount = runningRevCount;
if (passedMagnet && passingMagnet)
{ //Started a new pass of the magnet
passedMagnet = false;
newRevCount++;
}
else if (!passedMagnet && !passingMagnet)
{ //The new pass of the magnet is complete
passedMagnet = true;
}
return newRevCount;
}
unsigned long elapsedTime = 0;
unsigned long intervalTime = 0;
int rev = 0;
void loop()
{
intervalTime = millis() - elapsedTime;
rev = incrementRevolutions(rev, digitalRead(digitalPin));
// Serial.printf("outside rev: %d \n", rev);
if (intervalTime > 1000)
{
Serial.printf("rev: %d \n", rev);
rev = 0;
elapsedTime = millis();
}
}
這是 Arduino 或 C++ 編程的已知問題嗎? 我應該怎么做才能修復它?
我認為測試是罪魁禍首。 我不得不重命名並移動一些東西以可視化邏輯,對此感到抱歉。
bool magStateOld = false; // initialize to digitalRead(digitalPin) in setup()
int incrementRevolutions(int runningRevCount, bool magState)
{
int newRevCount = runningRevCount;
// detect positive edge.
if (magState && !magStateOld) // <- was eq. to if (magState && magStateOld)
// the large counts came from here.
{
newRevCount++;
}
magStateOld = magState; // record last state unconditionally
return newRevCount;
}
你也可以寫成...
int incrementRevolutions(int n, bool magState)
{
n += (magState && !magStateOld);
magStateOld = magState;
return n;
}
但是做你想做的最經濟(和最快)的方法是:
bool magStateOld;
inline bool positiveEdge(bool state, bool& oldState)
{
bool result = (state && !oldState);
oldState = state;
return result;
}
void setup()
{
// ...
magStateOld = digitalRead(digitalPin);
}
void loop()
{
// ...
rev += (int)positiveEdge(digitalRead(digitalPin), magStateOld);
// ...
}
它是可重用的,並且節省了堆棧空間和不必要的分配。
如果您無法從傳感器獲得干凈的轉換(正邊緣和負邊緣的噪聲,則需要使用計時器對信號進行一點去抖動。
例子:
constexpr byte debounce_delay = 50; // ms, you may want to play with
// this value, smaller is better.
// but must be high enough to
// avoid issues on expected
// RPM range.
// 50 ms is on the high side.
byte debounce_timestamp; // byte is large enough for delays
// up to 255ms.
// ...
void loop()
{
// ...
byte now = (byte)millis();
if (now - debounce_timestamp >= debounce_delay)
{
debounce_timestamp = now;
rev += (int)positiveEdge(digitalRead(digitalPin), magStateOld);
}
// ...
}
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