Arduino Interrupt misbehaving - arduino

Question

I'm having some problems with some C code I'm writing for an arduino project. The goal is to digitize a large quantity of analog signals with external multiplexed ADCs, then load these digital values into an external shift register and shift them into the Arduino using SPI.To test my code I only have one ADC multiplexing 4 signals.
The interrupt pin (20) is connected to a comparator circuit which looks at the raw analog signal and pulls the pin high when the voltage is 1V or higher. When the ISR is called it will disable global interrupts "noInterrupts()" set an event flag, detach pin 20 from the interrupt handler, enable global interrupts "interrupts()" and finally return to where it left off.
I'm facing a couple issues, first the ISR is called once fine, a second time fine but after the second ISR call it is not called again untill, which is my seconds issue, the interrupt pin goes low. As per the AttachInterupt() function the ISR should only be called when pin 20 is high. This can be seen in the first and second picture I have attached. Another thing I notice is that the duration that the interrupt pin is high has no effect on whether a 3rd ISR is called.
I'm not sure if this is an issue with my understanding of the interrupt-handling of the Arduino, or a code screw up resulting in a stack overflow or something like that.
// the sensor communicates using SPI, so include the library:
#include <SPI.h>
//Constants
#define RD 41 //pin 41 conneced to read pin
#define INT1 37 //pin 37 connecte to interrupt 1
#define CLK_INH 53 //pin 53 connected to clk inhibit
#define LD 40 //pin 40 connected to load pin
#define INPUT_MAX 3 //input selector limit (Zero Indexed)
#define SENSORS 3 //how many sensors are used (Zero Indexed)
#define DATA_DUMP 38 //pin 29 controlls the data dump deature
#define BYTE_LEN 1 //number of ADC used
#define DEBUG1 17
#define DEBUG2 16
//Controls
unsigned char selector = 0; //ACD input selector
volatile byte eventFlag = LOW; //Control Flag, set to True when event occurs
bool lastButtonState = true;
//Counters
unsigned int i = 0; //eventLog[i]: event counter
unsigned int j = 0; //eventLog[i].data[j]: data counter
//Function Delcarations
unsigned char inputSelector (unsigned char my_selector);
void lockAndPop ();
void dataDump ();
void debug (int pin);
bool fallingEdge (bool); //check for a falling edge of a digital read
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void setup() {
// put your setup code here, to run once:
pinMode(RD, OUTPUT); //Read pin, 0 = begin analog conversion (ADC)
pinMode(INT1, INPUT); //Interrupt pin, 0 = conversion complete (ADC)
pinMode(CLK_INH, OUTPUT); //Clock inhibit pin, 1= no change on output (ShiftRegister)
pinMode(LD, OUTPUT); //Shift/Load pin, 1 = data is shifted (ShiftRegister)
pinMode(DATA_DUMP, INPUT);
pinMode(DEBUG1, OUTPUT);
pinMode(DEBUG2, OUTPUT);
DDRA = 0xFF; //Set port A to ouput
SPI.begin();
//SPI.mode1 Clock idel low CLOP = 0, Data sampled on falling edge CPHA = 1
SPI.beginTransaction(SPISettings(5000000, MSBFIRST, SPI_MODE1));
digitalWrite(RD, HIGH); //Stop conversion
digitalWrite(CLK_INH, HIGH); //No change on the output
digitalWrite(LD, LOW); //Load the shift register
digitalWrite(DEBUG1, LOW);
digitalWrite(DEBUG2, LOW);
attachInterrupt(digitalPinToInterrupt(20), pin_ISR, HIGH); //Call pin_ISR when pin20 goes high
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
typedef struct //event structure, containts a timestamp element and an array of 18 data points
{
unsigned long int timeStamp;
unsigned char data[SENSORS];
} Event;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
Event eventLog[200]; //an array of structures representing 200 events, once the 200 events have been filled the data will be printed
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void loop() {
if(fallingEdge(digitalRead(DATA_DUMP))){ //If there is falling edge on the data dump button, call the dataDump function
dataDump();
}
debug(DEBUG2);
if(eventFlag) //if the Event flag is set to true by ISR begin the conversion steps
{
debug(DEBUG1);
digitalWrite(RD,LOW); //Start conversion
while(digitalRead(INT1)){} //Wait for conversion to complete
eventLog[i].timeStamp = micros();
for (j=0; j<=SENSORS; j++) {
lockAndPop(); //lock digital value and reset conversion
PORTA = inputSelector(selector); //increment the selector pin
digitalWrite(RD, LOW); //Start new conversion
digitalWrite(CLK_INH, LOW); //Start the data transfer
eventLog[i].data[j] = SPI.transfer(0); //read a single byte from the SPI line
digitalWrite(CLK_INH, HIGH); //Inhibit clock
digitalWrite(LD, LOW);
while(digitalRead(INT1)){} //wait for previous conversion to end
}
i++;
digitalWrite(RD, HIGH);
selector = 0;
if(i>=200){
dataDump(); //if the event log hits 200 before a data dump is request, dump the data
}
eventFlag = LOW;
attachInterrupt(digitalPinToInterrupt(20), pin_ISR, HIGH);
}
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void pin_ISR() {
noInterrupts();
detachInterrupt(digitalPinToInterrupt(20));
eventFlag = HIGH;
interrupts();
return;
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
unsigned char inputSelector (unsigned char my_selector){
if(my_selector==INPUT_MAX){ //if the current selector is at the highest value reset to 0
return 0;
}
return my_selector++; //increment the input selector by 1
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void lockAndPop (){
digitalWrite(LD, HIGH); //Lock in digital value
digitalWrite(RD, HIGH); //Reset conversion
return;
}
void dataDump (){
detachInterrupt(digitalPinToInterrupt(20));
char buf[100], *pos = buf; //create a buffer of 100 charaters, anda pointer to the begining of that buffer
char *base = buf; //create a base address to reset the buffer
unsigned int eventCount = i; //how many events occured before dump command was called
unsigned int localCount;
unsigned int localData;
Serial.begin(115200);
Serial.println(i);
for (localCount = 0; localCount<=eventCount; localCount++){
pos += sprintf(pos, "%lu", eventLog[localCount].timeStamp); //sprintf will append the data to the pointer "pos", and return the number of byte append.
for (localData = 0; localData<=SENSORS; localData++){
pos += sprintf(pos, " %d", (unsigned int)(eventLog[localCount].data[localData]));
}
Serial.println(buf);
pos = base;
}
i=0;
j=0;
Serial.end();
attachInterrupt(digitalPinToInterrupt(20), pin_ISR, HIGH);
return;
}
void debug(int pin){
digitalWrite(pin, HIGH);
digitalWrite(pin, LOW);
return;
}
bool fallingEdge (bool currentButtonState){
if(!currentButtonState&&lastButtonState){
lastButtonState = currentButtonState;
return 1;
}
lastButtonState = currentButtonState;
return 0;
}
There is a bit of noise happening on the ISR pin, but this shouldn't matter as I'm disabled that particular pin within the service routine so I wouldn't think this is an issue