b5ac95b274
Implement semaphore and mutex to safeguard the ISR. This is the proper way to handle hardware Interrupts with FreeRTOS. The more regular approach may/will lead to exceptions
83 lines
2.2 KiB
C++
83 lines
2.2 KiB
C++
/*
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Repeat timer example
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This example shows how to use hardware timer in ESP32. The timer calls onTimer
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function every second. The timer can be stopped with button attached to PIN 0
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(IO0).
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This example code is in the public domain.
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*/
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// Stop button is attached to PIN 0 (IO0)
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#define BTN_STOP_ALARM 0
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hw_timer_t * timer = NULL;
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volatile SemaphoreHandle_t timerSemaphore;
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portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;
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volatile uint32_t isrCounter = 0;
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volatile uint32_t lastIsrAt = 0;
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void IRAM_ATTR onTimer(){
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// Increment the counter and set the time of ISR
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portENTER_CRITICAL_ISR(&timerMux);
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isrCounter++;
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lastIsrAt = millis();
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portEXIT_CRITICAL_ISR(&timerMux);
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// Give a semaphore that we can check in the loop
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xSemaphoreGiveFromISR(timerSemaphore, NULL);
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// It is safe to use digitalRead/Write here if you want to toggle an output
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}
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void setup() {
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Serial.begin(115200);
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// Set BTN_STOP_ALARM to input mode
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pinMode(BTN_STOP_ALARM, INPUT);
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// Create semaphore to inform us when the timer has fired
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timerSemaphore = xSemaphoreCreateBinary();
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// Use 1st timer of 4 (counted from zero).
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// Set 80 divider for prescaler (see ESP32 Technical Reference Manual for more
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// info).
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timer = timerBegin(0, 80, true);
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// Attach onTimer function to our timer.
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timerAttachInterrupt(timer, &onTimer, true);
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// Set alarm to call onTimer function every second (value in microseconds).
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// Repeat the alarm (third parameter)
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timerAlarmWrite(timer, 1000000, true);
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// Start an alarm
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timerAlarmEnable(timer);
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}
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void loop() {
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// If Timer has fired
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if (xSemaphoreTake(timerSemaphore, 0) == pdTRUE){
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uint32_t isrCount = 0, isrTime = 0;
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// Read the interrupt count and time
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portENTER_CRITICAL(&timerMux);
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isrCount = isrCounter;
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isrTime = lastIsrAt;
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portEXIT_CRITICAL(&timerMux);
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// Print it
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Serial.print("onTimer no. ");
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Serial.print(isrCount);
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Serial.print(" at ");
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Serial.print(isrTime);
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Serial.println(" ms");
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}
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// If button is pressed
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if (digitalRead(BTN_STOP_ALARM) == LOW) {
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// If timer is still running
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if (timer) {
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// Stop and free timer
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timerEnd(timer);
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timer = NULL;
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}
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}
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}
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