RPM_Measure.ino

/****************************************************************************************************************************
  RPM_Measure.ino
  RPi_Pico_ISR_Timer-Impl.h
  For RP2040-based boards such as RASPBERRY_PI_PICO, ADAFRUIT_FEATHER_RP2040 and GENERIC_RP2040.
  Written by Khoi Hoang

  Built by Khoi Hoang https://github.com/khoih-prog/RPI_PICO_TimerInterrupt
  Licensed under MIT license

  The RPI_PICO system timer peripheral provides a global microsecond timebase for the system, and generates
  interrupts based on this timebase. It supports the following features:
    • A single 64-bit counter, incrementing once per microsecond
    • This counter can be read from a pair of latching registers, for race-free reads over a 32-bit bus.
    • Four alarms: match on the lower 32 bits of counter, IRQ on match: TIMER_IRQ_0-TIMER_IRQ_3

  Now even you use all these new 16 ISR-based timers,with their maximum interval practically unlimited (limited only by
  unsigned long miliseconds), you just consume only one RPI_PICO timer and avoid conflicting with other cores' tasks.
  The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers
  Therefore, their executions are not blocked by bad-behaving functions / tasks.
  This important feature is absolutely necessary for mission-critical tasks.
*****************************************************************************************************************************/
/*
   Notes:
   Special design is necessary to share data between interrupt code and the rest of your program.
   Variables usually need to be "volatile" types. Volatile tells the compiler to avoid optimizations that assume
   variable can not spontaneously change. Because your function may change variables while your program is using them,
   the compiler needs this hint. But volatile alone is often not enough.
   When accessing shared variables, usually interrupts must be disabled. Even with volatile,
   if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly.
   If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled
   or the entire sequence of your code which accesses the data.

   RPM Measuring uses high frequency hardware timer 1Hz == 1ms) to measure the time from of one rotation, in ms
   then convert to RPM. One rotation is detected by reading the state of a magnetic REED SW or IR LED Sensor
   Asssuming LOW is active.
   For example: Max speed is 600RPM => 10 RPS => minimum 100ms a rotation. We'll use 80ms for debouncing
   If the time between active state is less than 8ms => consider noise.
   RPM = 60000 / (rotation time in ms)

   You can also use interrupt to detect whenever the SW is active, set a flag then use timer to count the time between active state
*/

// These define's must be placed at the beginning before #include "TimerInterrupt_Generic.h"
// _TIMERINTERRUPT_LOGLEVEL_ from 0 to 4
// Don't define _TIMERINTERRUPT_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
#define TIMER_INTERRUPT_DEBUG         1
#define _TIMERINTERRUPT_LOGLEVEL_     4

// Can be included as many times as necessary, without `Multiple Definitions` Linker Error
#include "RPi_Pico_TimerInterrupt.h"

#define PIN_D1              1         // Pin D1 mapped to pin GPIO1 of RPI_PICO

unsigned int SWPin = PIN_D1;

#define TIMER0_INTERVAL_MS        1
#define DEBOUNCING_INTERVAL_MS    80

#define LOCAL_DEBUG               1

// Init RPI_PICO_Timer, can use any from 0-15 pseudo-hardware timers
RPI_PICO_Timer ITimer0(0);

volatile unsigned long rotationTime = 0;
float RPM       = 0.00;
float avgRPM    = 0.00;

volatile int debounceCounter;

bool TimerHandler0(struct repeating_timer *t)
{  
  (void) t;
  
  if ( !digitalRead(SWPin) && (debounceCounter >= DEBOUNCING_INTERVAL_MS / TIMER0_INTERVAL_MS ) )
  {
    //min time between pulses has passed
    RPM = (float) ( 60000.0f / ( rotationTime * TIMER0_INTERVAL_MS ) );

    avgRPM = ( 2 * avgRPM + RPM) / 3,

#if (TIMER_INTERRUPT_DEBUG > 0)
      Serial.print("RPM = "); Serial.print(avgRPM);
      Serial.print(", rotationTime ms = "); Serial.println(rotationTime * TIMER0_INTERVAL_MS);
#endif

    rotationTime = 0;
    debounceCounter = 0;
  }
  else
  {
    debounceCounter++;
  }

  if (rotationTime >= 5000)
  {
    // If idle, set RPM to 0, don't increase rotationTime
    RPM = 0;
    
#if (TIMER_INTERRUPT_DEBUG > 0)   
    Serial.print("RPM = "); Serial.print(RPM); Serial.print(", rotationTime = "); Serial.println(rotationTime);
#endif
    
    rotationTime = 0;
  }
  else
  {
    rotationTime++;
  }

  return true;
}

void setup()
{
  pinMode(SWPin, INPUT_PULLUP);
  
  Serial.begin(115200);
  while (!Serial);

  delay(100);
  
  Serial.print(F("\nStarting RPM_Measure on ")); Serial.println(BOARD_NAME);
  Serial.println(RPI_PICO_TIMER_INTERRUPT_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));

  // Using ESP32  => 80 / 160 / 240MHz CPU clock ,
  // For 64-bit timer counter
  // For 16-bit timer prescaler up to 1024

  // Interval in microsecs
  if (ITimer0.attachInterruptInterval(TIMER0_INTERVAL_MS * 1000, TimerHandler0))
  {
    Serial.print(F("Starting  ITimer0 OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer0. Select another freq. or timer"));

  Serial.flush();   
}

void loop()
{

}