ESP8266 (WEMOS D1) Zero Cross Triac using Timer0 (higher resolution/quality than Timer1)

ESP8266-ZeroCrossTriac-Timer0

#define TIMR_OVRHD 7000

uint8_t _z = 0;
uint32_t _v = 20000;

void ICACHE_RAM_ATTR _ISR0() {
  if (_z == 1) {
    _z = 2;
    timer0_write(ESP.getCycleCount() + 8000); // 8000 = 100us, 80000 = 1ms
    digitalWrite(D2, HIGH);
  }
  else if (_z == 2) {
    digitalWrite(D2, LOW);
    timer0_detachInterrupt(); // Must detach interrupt handler before next time it is attached to avoid ESP crash
    _z = 0;
  }
}

void ICACHE_RAM_ATTR _ZC() {
  _z = 1;
  timer0_attachInterrupt(_ISR0); // Attaching interrupt handler here avoids ESP crash
  timer0_write(ESP.getCycleCount() + TIMR_OVRHD + _v);
}

void setup() {
  Serial.begin(74880);
  timer0_isr_init(); // Attaching the interrupt handler here causes the ESP to crash
  pinMode(D2, OUTPUT);
  digitalWrite(D2, LOW);
  pinMode(D3, INPUT_PULLUP);
  attachInterrupt(D3, _ZC, RISING);
  Serial.printf("\n\n");
}

uint32_t _t = millis();
uint8_t _d = 1;

void loop() {
  uint32_t t = millis();
  if (t - _t > 100) {
    _v += _d ? 20000 : -20000;
    if (_v == 20000 || _v == 640000) _d = !_d;
    _t = t;
  }
}