// uart-slave-green.ino — Node 2 (slave B), XIAO ESP32-S3
// Week 11 — same logic as slave A but NID 2 and green LED. The ESP32-S3 needs
// Serial1 remapped to its UART pins (RX = GPIO44, TX = GPIO43).
 
#define MY_NID      2     // this board is NID 2 (green)
#define NID_MASTER  0
 
#define FRAME_START 0xFF
#define CMD_LED     0x03
#define LED_PIN     2     // GPIO2 (D1), green LED via 220 ohm to GND
#define UART_RX     44    // GPIO44 (D7)
#define UART_TX     43    // GPIO43 (D6) - unused here, declared for completeness
 
uint8_t buf[6];
uint8_t idx = 0;
 
void handleFrame() {
  uint8_t dest = buf[1], src = buf[2], cmd = buf[3], payload = buf[4], chk = buf[5];
 
  if ((uint8_t)(dest ^ src ^ cmd ^ payload) != chk) {
    Serial.println("RX  bad checksum, frame dropped");
    return;
  }
  if (dest != MY_NID) {
    Serial.print("RX  frame for NID ");
    Serial.print(dest);
    Serial.println(" - not me, ignored");
    return;
  }
  if (cmd == CMD_LED) {
    digitalWrite(LED_PIN, payload ? HIGH : LOW);
    Serial.print("RX  DEST_NID=2 (me)  LED=");
    Serial.println(payload ? "ON" : "OFF");
  }
}
 
void setup() {
  Serial.begin(9600);                              // USB monitor
  Serial1.begin(9600, SERIAL_8N1, UART_RX, UART_TX); // UART bus
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  Serial.println("Slave B (NID 2, green LED) ready.");
}
 
void loop() {
  while (Serial1.available()) {
    uint8_t b = Serial1.read();
    if (idx == 0 && b != FRAME_START) continue;   // resync: wait for START
    buf[idx++] = b;
    if (idx == 6) {
      idx = 0;
      handleFrame();
    }
  }
}