Minimal case of interrupt handler causing crash on ESP8266. Compile with `ENABLE_WIFI` to see the crash. For https://github.com/puuu/ESPiLight/pull/9

main.cpp

#include <Arduino.h>
#include <ESPiLight.h>

#ifdef ENABLE_WIFI
#include <ESP8266WiFi.h>

#define WIFI_SSID "myssid"
#define WIFI_PSK "mypassphrase"
#endif

#define TRANSMITTER_PIN -1
#define RECEIVER_PIN 4

ESPiLight rf(TRANSMITTER_PIN);

void rfCallback(const uint16_t* codes, int length) {
    Serial.printf("Received length %d\n", length);
}

void setup(void) {
    Serial.begin(9600);

    #ifdef ENABLE_WIFI
    Serial.print(F("Setting up wifi connection..."));
    WiFi.disconnect(true);
    WiFi.mode(WIFI_STA);
    WiFi.begin(WIFI_SSID, WIFI_PSK);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(F("."));
    }
    Serial.println(F(" done."));
    #endif

    rf.setPulseTrainCallBack(rfCallback);
    rf.initReceiver(RECEIVER_PIN);
}

void loop(void) {
    rf.loop();
    delay(10);
}