ESP8266 GPIO expander missing interrupts - arduino

Question

I have a program that lets an LED pulse. I also connected the PC8574 GPIO expander with a push button. I want to evaluate the keypress. However, I can only read the status of the INT (interrupt) while the program is in the part between making the LED brighter and making it darker again (between the two for loops)
I know that the problem is the delays withing the for loops but I have no idea how to avoid that.
Would it be possible to evaluate the interrupt related code more often or like a real interrupt - always when the actual key is pressed? And if so, how?
I use this library: https://github.com/WereCatf/PCF8574_ESP
/*LED_Breathing.ino Arduining.com 20 AUG 2015
Using NodeMCU Development Kit V1.0
Going beyond Blink sketch to see the blue LED breathing.
A PWM modulation is made in software because GPIO16 can't
be used with analogWrite().
*/
#include <pcf8574_esp.h>
#include <Wire.h>
TwoWire testWire;
// Initialize a PCF8574 at I2C-address 0x20, using GPIO5, GPIO4 and testWire for the I2C-bus
PCF857x pcf8574(0x20, &testWire);
#define LED D1 // Led in NodeMCU at pin GPIO16 (D0).
#define BRIGHT 300 //max led intensity (1-500)
#define INHALE 1250 //Inhalation time in milliseconds.
#define PULSE INHALE*1000/BRIGHT
#define REST 1000 //Rest Between Inhalations.
#define PIN_INT D5
#define PIN_SDA D7
#define PIN_SCL D8
//----- Setup function. ------------------------
void setup() {
Serial.begin(115200);
Wire.pins(PIN_SDA, PIN_SCL);//SDA - D1, SCL - D2
Wire.begin();
pinMode(PIN_INT, INPUT_PULLUP);
pcf8574.begin( 0xFF);
pcf8574.resetInterruptPin();
pinMode(LED, OUTPUT); // LED pin as output.
}
bool CheckKey(byte key, byte num){ //0, 1, 2, 3
return key & (1 << num);
}
//----- Loop routine. --------------------------
void loop() {
//ramp increasing intensity, Inhalation:
for (int i=1;i<BRIGHT;i++){
digitalWrite(LED, LOW); // turn the LED on.
delayMicroseconds(i*10); // wait
digitalWrite(LED, HIGH); // turn the LED off.
delayMicroseconds(PULSE-i*10); // wait
delay(0); //to prevent watchdog firing.
}
if( digitalRead(PIN_INT)==LOW ){
delay(50);
byte b = pcf8574.read8();
Serial.println( "INT: " + String(b));
byte keys = ((~b)) & 0x0F;
if( CheckKey(keys, 8) ){
Serial.println( "KEY 7");
delay(2000);
}
}
//ramp decreasing intensity, Exhalation (half time):
for (int i=BRIGHT-1;i>0;i--){
digitalWrite(LED, LOW); // turn the LED on.
delayMicroseconds(i*10); // wait
digitalWrite(LED, HIGH); // turn the LED off.
delayMicroseconds(PULSE-i*10); // wait
i--;
delay(0); //to prevent watchdog firing.
}
delay(REST); //take a rest...
}

Answer 1

You could use the PCF8574 INT pin as an interrupt to the ESP8266 via Arduino's attachInterrupt() function, but you wouldn't gain much from that, since in order to detect which key was pressed you need to call pcf8574.read8(), and you can't do that from the interrupt handler.
The ESP8266 Arduino core is based on the Espressif NONOS SDK, so you can't have a separate thread to monitor key presses. I would suggest defining a helper function that checks if a key is currently being pressed, and then calling that function as often as you can in your main loop, e.g. at every iteration of each of your two for loops. The LED brightness ramps would be slightly disrupted when there is a key press, but I think it wouldn't be noticeable to the human eye.
So the helper function could be defined as:
byte GetKeyPress(void) {
if (digitalRead(PIN_INT) == LOW) {
return ~pcf8574.read8();
}
else {
return 0;
}
}
Then, at the beginning of the loop() function declare a static variable static byte keyPress;, and call the above function in each of the two for loops:
if (keyPress == 0) {
keyPress = GetKeyPress();
}
When you want to process a key press (e.g. between the two for loops like in your code), you can do like that:
if (keyPress) {
/* Do your stuff. */
keyPress = 0;
}