Interfacing to Adafruit fingerprint sensor

I'm just copying a some code here from a PM. @ChrisB was asking about the Adafruit fingerprint sensor...

• Adafruit Library
  
• Adafruit example
  
• Datasheet
  
  

Connections:

The module itself needs writing to that it can cope with the 'timeout' used by Adafruit's module while still allowing tasks to run in the background - so it needs to use callbacks...

So far, the initial suggested module looks like:

receivedData=[];
Serial4.setup(57600);
Serial4.onData(function (e) { receivedData.push(e.data.charCodeAt(0)); });

var C = {
OK: 0x00,
PACKETRECIEVEERR: 0x01,
NOFINGER: 0x02,
IMAGEFAIL: 0x03,
IMAGEMESS: 0x06,
FEATUREFAIL: 0x07,
NOMATCH: 0x08,
NOTFOUND: 0x09,
ENROLLMISMATCH: 0x0A,
BADLOCATION: 0x0B,
DBRANGEFAIL: 0x0C,
UPLOADFEATUREFAIL: 0x0D,
PACKETRESPONSEFAIL: 0x0E,
UPLOADFAIL: 0x0F,
DELETEFAIL: 0x10,
DBCLEARFAIL: 0x11,
PASSFAIL: 0x13,
INVALIDIMAGE: 0x15,
FLASHERR: 0x18,
INVALIDREG: 0x1A,
ADDRCODE: 0x20,
PASSVERIFY: 0x21,
STARTCODE: 0xEF01,
COMMANDPACKET: 0x1,
DATAPACKET: 0x2,
ACKPACKET: 0x7,
ENDDATAPACKET: 0x8,
TIMEOUT: 0xFF,
BADPACKET: 0xFE,
GETIMAGE: 0x01,
IMAGE2TZ: 0x02,
REGMODEL: 0x05,
STORE: 0x06,
EMPTY: 0x0D,
VERIFYPASSWORD: 0x13,
HISPEEDSEARCH: 0x1B,
TEMPLATECOUNT: 0x1D
};

var thePassword = 0;
var theAddress = 0xFFFFFFFF;

function writePacket(addr, packetType, packet) {
  var len = packet.length+2;
  Serial4.write([
        (C.STARTCODE >> 8) & 0xFF), 
        C.STARTCODE & 0xFF,
        (addr >> 24) & 0xFF,
        (addr >> 16) & 0xFF,
        (addr >> 8) & 0xFF,
        addr & 0xFF,
        packetType,
        (len >> 8) & 0xFF,
        len &0xFF]);
  
  var sum = (len>>8) + (len&0xFF) + packetType;
  Serial4.write(packet);
  for (var i in packet) sum += packet[i];
  Serial4.write([(sum>>8)&0xFF, sum&0xFF])
}

function getReply(callback) {
  receivedData=[];
  setTimeout(function() {
   // do some checks here?
   callback(receivedData);
  }, 500); // 500ms
}


function verifyPassword(callback) {
  var packet = [
    C.VERIFYPASSWORD, 
    (thePassword >> 24) & 0xFF, 
    (thePassword >> 16) & 0xFF,
    (thePassword >> 8) & 0xFF, 
    thePassword & 0xFF
  ];
  writePacket(theAddress, C.COMMANDPACKET, packet);
  getReply(function(packet) {
   callback((packet[0] == C.ACKPACKET) && (packet[1] == C.OK));
  });    
}