// clar200_bridge.ino — ESP32-C3 transparent USB <-> UART bridge
// Purpose: talk to a Seagate F3 diagnostic terminal on an EMC CLAR200-locked
//          Exos X18 SAS drive, using the C3's native USB-CDC as the host side.
//
// Target board: ESP32-C3 (native USB-Serial-JTAG), e.g. C3 SuperMini / DevKitM-1.
// Host port:    /dev/ttyACM0 on steel141 (MAC 58:8c:81:ac:f0:4c).
//
// Build flag REQUIRED: "USB CDC On Boot: Enabled"  (so `Serial` == USB-CDC, not UART0)
//   arduino-cli: append  :CDCOnBoot=cdc  to the FQBN (see firmware/flash.sh)
//
// Wiring (3.3 V, common ground, TX<->RX crossover):
//   ESP32-C3 GPIO4 (DRV_TX) ---> drive F3 RX
//   ESP32-C3 GPIO5 (DRV_RX) <--- drive F3 TX
//   ESP32-C3 GND            ---- drive GND   (mandatory)
//   Do NOT connect any VCC/5V to the drive header. Drive is powered by its own
//   SATA/SAS power. You only tap TX / RX / GND.
//
// Baud: Seagate F3 is 8N1. Family varies — this sketch boots at 38400 and lets
// you change baud live without reflashing, via a `~` escape menu (see below).
//
// Live baud menu — type these AT THE START OF A LINE in your terminal:
//   ~1  -> 9600     ~2 -> 38400 (default)    ~3 -> 115200    ~4 -> 460800
//   ~?  -> print current baud
// Anything else is passed through transparently (binary-safe).

#define DRV_TX   4          // ESP32-C3 GPIO -> drive RX
#define DRV_RX   5          // ESP32-C3 GPIO <- drive TX
#define LED_PIN  8          // most C3 boards: onboard LED on GPIO8 (active-low). Harmless if absent.

static const uint32_t BAUDS[] = {9600, 38400, 115200, 460800};
static uint32_t curBaud = 38400;

static void applyBaud(uint32_t b) {
  curBaud = b;
  Serial1.end();
  Serial1.begin(curBaud, SERIAL_8N1, DRV_RX, DRV_TX);
  Serial.printf("\r\n[bridge] drive UART = %lu 8N1\r\n", (unsigned long)curBaud);
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);          // LED on = bridge alive
  Serial.begin(115200);                // USB-CDC; baud value is ignored over CDC
  delay(200);
  applyBaud(38400);
  Serial.print("\r\n[bridge] ESP32-C3 F3 bridge ready. ~1/~2/~3/~4 set baud, ~? shows it.\r\n");
}

// Minimal line-start escape parser so `~N` switches baud but everything else
// (including F3 binary) flows through untouched.
static bool atLineStart = true;
static bool inEscape = false;

void loop() {
  // host -> drive
  while (Serial.available()) {
    int c = Serial.read();
    if (inEscape) {
      inEscape = false;
      switch (c) {
        case '1': applyBaud(BAUDS[0]); break;
        case '2': applyBaud(BAUDS[1]); break;
        case '3': applyBaud(BAUDS[2]); break;
        case '4': applyBaud(BAUDS[3]); break;
        case '?': Serial.printf("\r\n[bridge] current = %lu\r\n", (unsigned long)curBaud); break;
        default:  // not a menu key: emit the swallowed '~' then this char
          Serial1.write('~'); Serial1.write((uint8_t)c);
      }
      atLineStart = false;
      continue;
    }
    if (atLineStart && c == '~') { inEscape = true; continue; }
    Serial1.write((uint8_t)c);
    atLineStart = (c == '\n' || c == '\r');
  }
  // drive -> host
  while (Serial1.available()) Serial.write((uint8_t)Serial1.read());
}