gistfile1.txt

#include <string.h>
#include <SoftwareSerial.h>

SoftwareSerial rfid(3, 2);

void check_for_notag(void);
void rfid_halt(void);
void parse(void);
void print_serial(void);
void read_serial(void);
void rfid_seek(void);
void set_flag(void);

uint8_t tag[] = { 0x87, 0x9D, 0x64, 0x02 };

enum RfidCmd
{
  RESET    = 0x80,
  FIRMWARE = 0x81,
  SEEK     = 0x82,
  POWER    = 0x90,
  HALT     = 0x93
};

void setup()  
{
  Serial.begin(9600);
  Serial.println("Start I");
}

void loop()                 
{
  if (rfid_do_id(millis() + 5000))
    Serial.println("identified");
  else
    Serial.println("timed out");
}

void rfid_send_frame(uint8_t cmd, uint8_t *data, uint8_t length)
{
  uint8_t payload_length = length + 1;
  uint8_t checksum = 0x00 + payload_length + cmd;
  rfid.write((uint8_t)0xFF);			// header
  rfid.write((uint8_t)0x00);			// reserved, unimplimented
  rfid.write((uint8_t)payload_length);		// payload byte count including cmd
  rfid.write((uint8_t)cmd);              	// command
  for (uint8_t i = 0; i < length; ++i)	// data
  {
    rfid.write(data[i]);
    checksum += data[i];
  }
  rfid.write((uint8_t)checksum);			// checksum ends packet
}

void rfid_halt(void)
{
  rfid_send_frame(HALT, 0, 0);
}

void rfid_seek()
{
  rfid_send_frame(SEEK, 0, 0);
  delay(10);
}

bool rfid_timeout_read(unsigned long expire_time, uint8_t *out)
{
  while (millis() < expire_time)
  {
    if (rfid.available() > 0)
    {
      *out = rfid.read();
      return true;
    }

    delay(20);
  }

  return false;
}

bool rfid_read_seek_response(unsigned long expire_time)
{
  uint8_t b;

  // ignore everything up to packet frame header
  while (1)
  {
    if (!rfid_timeout_read(expire_time, &b))
      return false;
    if (b == 0xFF)
      break;
   }

  // require rest of packet header
  if (!rfid_timeout_read(expire_time, &b) || b != 0x00)
    return false;
  
  if (!rfid_timeout_read(expire_time, &b) || b != 0x02)
    return false;

  // require seek command reply
  if (!rfid_timeout_read(expire_time, &b) || b != SEEK)
    return false;
  
  // require success
  if (!rfid_timeout_read(expire_time, &b) || b != 0x4C)
    return false;

  // require checksum
  if (!rfid_timeout_read(expire_time, &b) || b != 0xD0)
    return false;

  return true;  
}

bool rfid_cmp_tag_packet(unsigned long expire_time)
{
  uint8_t l, b;

  // ignore everything up to packet frame header
  while (1)
  {
    if (!rfid_timeout_read(expire_time, &b))
      return false;
    if (b == 0xFF)
      break;
   }

  // require reserved byte
  if (!rfid_timeout_read(expire_time, &b) || b != 0x00)
    return false;                             // bad packet frame

  // read payload length. needs to be a sensible tag length
  if (!rfid_timeout_read(expire_time, &b) || (b != 6 && b != 9))
    return false;

  // ought to be a reply to a seek command
  if (!rfid_timeout_read(expire_time, &b) || b != SEEK)
    return false;

  // ignore "tag type" byte
  if (!rfid_timeout_read(expire_time, &b))
    return false;

  for (int i = l - 3; i >= 0; --i)
  {
    if (!rfid_timeout_read(expire_time, &b))
      return false;
    if (tag[i] != b)
    {
      Serial.print(tag[i], HEX);
      Serial.print(" != ");
      Serial.println(b, HEX);
      return false;
    }
  }
  return true;
}

bool rfid_do_id(unsigned long expire_time)
{
  rfid.begin(19200);
  delay(10);

  while (millis() < expire_time)
  {
    rfid_seek();
    delay(10);

    if (!rfid_read_seek_response(expire_time))
    {
      rfid.end();
      return false;
    }

    if (rfid_cmp_tag_packet(expire_time))
    {
      rfid.end();
      return true;
    }
  }
  rfid.end();
  return false;
}