mfrc522: Add support for 7-bytes UUID (#442)

Add ReadUID example.

experimental/devices/mfrc522/commands/low_level.go

@@ -35,9 +35,9 @@ type AuthStatus byte
 
 // NewLowLevelSPI creates and initializes the RFID card reader attached to SPI.
 //
-// 	spiPort - the SPI device to use.
-// 	resetPin - reset GPIO pin.
-// 	irqPin - irq GPIO pin.
+//  spiPort - the SPI device to use.
+//  resetPin - reset GPIO pin.
+//  irqPin - irq GPIO pin.
 func NewLowLevelSPI(spiPort spi.Port, resetPin gpio.PinOut, irqPin gpio.PinIn) (*LowLevel, error) {
 	if resetPin == nil {
 		return nil, wrapf("reset pin is not set")

experimental/devices/mfrc522/commands/picc.go

@@ -17,6 +17,7 @@ const (
 	PICC_REQIDL    = 0x26
 	PICC_REQALL    = 0x52
 	PICC_ANTICOLL  = 0x93
+	PICC_ANTICOLL2 = 0x95
 	PICC_SElECTTAG = 0x93
 	PICC_AUTHENT1A = 0x60
 	PICC_AUTHENT1B = 0x61

experimental/devices/mfrc522/example_test.go

@@ -23,7 +23,7 @@ func Example() {
 		log.Fatal(err)
 	}
 
-	// Using SPI as an example. See package ./spi/spireg for more details.
+	// Using SPI as an example. See package "periph.io/x/periph/conn/spi/spireg" for more details.
 	p, err := spireg.Open("")
 	if err != nil {
 		log.Fatal(err)
@@ -102,3 +102,75 @@ func Example() {
 		}
 	}
 }
+
+func ExampleDev_ReadUID() {
+	// Make sure periph is initialized.
+	if _, err := host.Init(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Using SPI as an example. See package "periph.io/x/periph/conn/spi/spireg" for more details.
+	p, err := spireg.Open("")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer p.Close()
+
+	rfid, err := mfrc522.NewSPI(p, rpi.P1_22, rpi.P1_18)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Idling device on exit.
+	defer rfid.Halt()
+
+	// Setting the antenna signal strength.
+	rfid.SetAntennaGain(5)
+
+	timedOut := false
+	cb := make(chan []byte)
+	timer := time.NewTimer(10 * time.Second)
+
+	// Stopping timer, flagging reader thread as timed out
+	defer func() {
+		timer.Stop()
+		timedOut = true
+		close(cb)
+	}()
+
+	go func() {
+		log.Printf("Started %s", rfid.String())
+
+		for {
+			// Trying to read card UID.
+			uid, err := rfid.ReadUID(10 * time.Second)
+
+			// If main thread timed out just exiting.
+			if timedOut {
+				return
+			}
+
+			// Some devices tend to send wrong data while RFID chip is already detected
+			// but still "too far" from a receiver.
+			// Especially some cheap CN clones which you can find on GearBest, AliExpress, etc.
+			// This will suppress such errors.
+			if err != nil {
+				continue
+			}
+
+			cb <- uid
+			return
+		}
+	}()
+
+	for {
+		select {
+		case <-timer.C:
+			log.Fatal("Didn't receive device data")
+			return
+		case data := <-cb:
+			log.Println("UID:", hex.EncodeToString(data))
+			return
+		}
+	}
+}

experimental/devices/mfrc522/mfrc522.go

@@ -123,6 +123,20 @@ func (r *Dev) SetAntennaGain(gain int) error {
 	return nil
 }
 
+// ReadUID reads the card UID with IRQ event timeout.
+//
+//  timeout   the operation timeout
+func (r *Dev) ReadUID(timeout time.Duration) (uid []byte, err error) {
+	r.beforeCall()
+	defer func() {
+		r.afterCall()
+		if err == nil {
+			err = r.LowLevel.StopCrypto()
+		}
+	}()
+	return r.selectCard(timeout)
+}
+
 // ReadCard  reads the card sector/block with IRQ event timeout.
 //
 //  timeout   the operation timeout
@@ -303,6 +317,35 @@ func (r *Dev) antiColl() ([]byte, error) {
 	return backData, nil
 }
 
+// antiColl2 performs additional anticollision check for UIDs with more than 4 bytes.
+func (r *Dev) antiColl2() ([]byte, error) {
+	if err := r.LowLevel.DevWrite(commands.BitFramingReg, 0x00); err != nil {
+		return nil, err
+	}
+
+	serial := []byte{commands.PICC_ANTICOLL2, 0x20}
+	check := byte(0)
+
+	backData, _, err := r.LowLevel.CardWrite(commands.PCD_TRANSCEIVE, serial)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(backData) != 5 {
+		return nil, wrapf("Anticoll2 error, response is %d bytes-long, expected 5", len(backData))
+	}
+
+	for i := 0; i < 4; i++ {
+		check ^= backData[i]
+	}
+
+	if check != backData[4] {
+		return nil, wrapf("Anticoll2 error, check failed")
+	}
+
+	return backData, nil
+}
+
 // selectTag selects the FOB device by device UUID.
 func (r *Dev) selectTag(serial []byte) (byte, error) {
 	dataBuf := make([]byte, len(serial)+2)
@@ -355,6 +398,17 @@ func (r *Dev) selectCard(timeout time.Duration) ([]byte, error) {
 	if _, err := r.selectTag(uuid); err != nil {
 		return nil, err
 	}
+
+	if uuid[0] == 0x88 { // Incomplete UID
+		// Get remaining bytes
+		uuidEnd, err := r.antiColl2()
+		if err != nil {
+			return nil, err
+		}
+
+		uuid = uuid[1 : len(uuid)-1]
+		uuid = append(uuid, uuidEnd[:len(uuidEnd)-1]...)
+	}
 	return uuid, nil
 }