ESP32 UHF RFID inventory interface

Read the implementation

code.txt — framed UART receiver.

static bool readFrame(uint8_t &outCmd, uint8_t *buf, uint16_t &outLen, uint16_t timeoutMs = 300) {
  // Seek 0xBB
  uint32_t t0 = millis();
  while (millis() - t0 < timeoutMs) {
    if (Reader.available()) {
      if (Reader.read() == 0xBB) break;
    }
  }
  if (millis() - t0 >= timeoutMs) return false;

  uint8_t addr, cmd, lh, ll;
  if (!readByteWait(addr, timeoutMs)) return false;
  if (!readByteWait(cmd,  timeoutMs)) return false;
  if (!readByteWait(lh,   timeoutMs)) return false;
  if (!readByteWait(ll,   timeoutMs)) return false;

  uint16_t len = (uint16_t(lh) << 8) | ll;
  if (len > 512) return false; // sanity guard for our fixed buffer

  // Read payload
  for (uint16_t i = 0; i < len; i++) {
    if (!readByteWait(buf[i], timeoutMs)) return false;
  }

  // CS + tail
  uint8_t csh, csl, tail;
  if (!readByteWait(csh, timeoutMs)) return false;
  if (!readByteWait(csl, timeoutMs)) return false;
  if (!readByteWait(tail, timeoutMs)) return false;
  if (tail != 0x7E) return false;

  // (Optional) verify checksum
  uint32_t sum = addr + cmd + lh + ll;
  for (uint16_t i = 0; i < len; i++) sum += buf[i];
  uint16_t cs = sum & 0xFFFF;
  uint16_t got = (uint16_t(csh) << 8) | csl;
  if (cs != got) {
    Serial.print(F("[WARN] Checksum mismatch, calc=0x"));
    Serial.print(cs, HEX);
    Serial.print(F(" got=0x"));
    Serial.println(got, HEX);
  }

  outCmd = cmd;
  outLen = len;
  return true;