diff --git a/dbus_service/dbus-service b/dbus_service/dbus-service
index ff84755..dd8bc44 100755
--- a/dbus_service/dbus-service
+++ b/dbus_service/dbus-service
@@ -10,6 +10,7 @@ import dbus
 import dbus.mainloop.glib
 import dbus.service
 from binascii import hexlify, unhexlify
+from threading import Thread
 dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
 from gi.repository import GLib
 import logging
@@ -92,19 +93,21 @@ class Device(dbus.service.Object):
     def VerifyStart(self, user, finger):
         logging.debug('In VerifyStart %s' % finger)
 
-        def complete_cb(rsp, e):
-            if e is not None:
-                self.VerifyStatus('verify-no-match', True)
-            else:
-                self.VerifyStatus('verify-match', True)
-                usrid, subtype, hsh = rsp
-                # TODO pass down the user DB id
-                # check that a correct finger was identified
-
         def update_cb(e):
             self.VerifyStatus('verify-retry-scan', False)
 
-        sensor.identify(update_cb, complete_cb)
+        def run():
+            try:
+                usrid, subtype, hsh = sensor.identify(update_cb)
+                self.VerifyStatus('verify-match', True)
+            except Exception as e:
+                logging.exception('Oops', e)
+                self.VerifyStatus('verify-no-match', True)
+
+        thread = Thread(target=run)
+        thread.daemon = True
+        thread.start()
+        
 
     @dbus.service.method(dbus_interface=INTERFACE_NAME,
                          in_signature='',
@@ -112,18 +115,6 @@ class Device(dbus.service.Object):
     def Cancel(self):
         sensor.cancel()
 
-    def do_enroll(self, finger_name, uid):
-        # it is pointless to try and remember username passed in claim as Gnome does not seem to be passing anything useful anyway
-        try:
-            # TODO hardcode the username and finger for now
-            z=enroll(uid2identity(uid), 0xf5)
-            logging.debug('Enroll was successfull')
-            self.EnrollStatus('enroll-completed', True)
-        except Exception as e:
-            self.EnrollStatus('enroll-failed', True)
-            #loop.quit();
-            raise e
-
     @dbus.service.method(dbus_interface=INTERFACE_NAME,
                          in_signature='ss',
                          out_signature='')
@@ -137,13 +128,18 @@ class Device(dbus.service.Object):
             else:
                 self.EnrollStatus('enroll-stage-passed', False)
 
-        def complete_cb(rsp, e):
-            if e is not None:
-                self.EnrollStatus('enroll-failed', True)
-            else:
+        def run():
+            try:
+                sensor.enroll(uid2identity(uid), 0xf5, update_cb) # TODO parse the finger name
                 self.EnrollStatus('enroll-completed', True)
+            except Exception as e:
+                logging.exception('Oops', e)
+                self.EnrollStatus('enroll-failed', True)
 
-        sensor.enroll(uid2identity(uid), 0xf5, update_cb, complete_cb) # TODO parse the finger name
+        thread = Thread(target=run)
+        thread.daemon = True
+        thread.start()
+        
 
     @dbus.service.signal(dbus_interface=INTERFACE_NAME, signature='sb')
     def VerifyStatus(self, result, done):
diff --git a/scripts/prototype.py b/scripts/prototype.py
index 2d648f8..b015798 100644
--- a/scripts/prototype.py
+++ b/scripts/prototype.py
@@ -14,69 +14,21 @@ import code
 #tls.trace_enabled = True
 
 def identify():
-    cv=Condition()
-    result=[]
-
     def update_cb(e):
         print('Capture error: %s, try again' % repr(e))
 
-    def complete_cb(rsp, e):
-        cv.acquire()
-        try:
-            result.append((rsp, e))
-            cv.notify()
-        finally:
-            cv.release()
-
-    sensor.identify(update_cb, complete_cb)
-
-    cv.acquire()
-    try:
-        cv.wait()
-        rsp, e = result[0]
-        if e is not None: raise e
-
-    except:
-        sensor.cancel()
-        raise
-    finally:
-        cv.release()
-
-    usrid, subtype, hsh = rsp
+    usrid, subtype, hsh = sensor.identify(update_cb)
 
     print('Got finger %x for user recordid %d. Hash: %s' % (subtype, usrid, hexlify(hsh).decode()))
 
 def enroll(sid, finger):
-    cv=Condition()
-    result=[]
-
     def update_cb(x, e):
         if e is not None:
             print('Enroll error: %s, try again' % repr(e))
         else:
             print('Enroll progress: %s' % hexlify(x).decode())
 
-    def complete_cb(rsp, e):
-        cv.acquire()
-        try:
-            result.append((rsp, e))
-            cv.notify()
-        finally:
-            cv.release()
-
-    sensor.enroll(sid, finger, update_cb, complete_cb)
-
-    cv.acquire()
-    try:
-        cv.wait()
-        recid, e = result[0]
-        if e is not None: raise e
-
-    except:
-        sensor.cancel()
-        raise
-    finally:
-        cv.release()
+    recid = sensor.enroll(sid, finger, update_cb)
 
     print('Created a finger record with dbid %d' % recid)
 
diff --git a/validitysensor/db.py b/validitysensor/db.py
index 486b6d7..b6da5f2 100644
--- a/validitysensor/db.py
+++ b/validitysensor/db.py
@@ -6,7 +6,7 @@ from .util import assert_status
 from struct import pack, unpack
 from binascii import hexlify, unhexlify
 from .blobs import db_write_enable
-from .flash import flush_changes
+from .flash import call_cleanups
 from .sid import *
 
 class UserStorage():
@@ -125,6 +125,18 @@ class DbRecord():
             
 
 class Db():
+    class Info():
+        def __init__(self, total, used, free, records, roots):
+            self.total = total # partition size
+            self.used = used # used (not deleted)
+            self.free = free # unallocated space
+            self.records = records # total number, including deleted
+            self.roots = roots
+
+        def __repr__(self):
+            return 'Db.Info(total=%d, used=%d, free=%d, records=%d, roots=%s)' % (
+                    self.total, self.used, self.free, self.records, repr(self.roots))
+
     def get_user_storage(self, dbid=0, name=''):
         name=name.encode()
 
@@ -175,7 +187,7 @@ class Db():
         rsp = rsp[14:]
         rec.children=[]
         for i in range(0, cnt):
-            dbid, typ = unpack('<HH', rsp[i:i+4])
+            dbid, typ = unpack('<HH', rsp[i*4:i*4+4])
             rec.children += [{ 'dbid': dbid, 'type': typ }]
 
         return rec
@@ -183,14 +195,27 @@ class Db():
     def del_record(self, dbid):
         assert_status(tls.cmd(pack('<BH', 0x48, dbid)))
 
+    def db_info(self):
+        rsp = tls.cmd(b'\x45')
+        assert_status(rsp)
+        rsp = rsp[2:]
+
+        unknown1, unknown0, total, used, free, records, nroots = unpack('<LLLLLHH', rsp[:0x18])
+        # Seems to always be unknown1 == 1, unknown0 == 0
+        rsp = rsp[0x18:]
+        roots = [unpack('<H', rsp[i*2:i*2+2])[0] for i in range(0, nroots)]
+
+        return Db.Info(total, used, free, records, roots)
 
     def new_record(self, parent, typ, storage, data):
-        assert_status(tls.cmd(b'\x45'))
+        self.db_info() # TODO check free space, compact the partition when out of storage
         assert_status(tls.cmd(db_write_enable))
-        rsp = tls.cmd(pack('<BHHHH', 0x47, parent, typ, storage, len(data)) + data)
-        assert_status(rsp)
-        recid, = unpack('<H', rsp[2:])
-        flush_changes()
+        try:
+            rsp = tls.cmd(pack('<BHHHH', 0x47, parent, typ, storage, len(data)) + data)
+            assert_status(rsp)
+            recid, = unpack('<H', rsp[2:])
+        finally:
+            call_cleanups()
         return recid
 
     def new_user(self, identity):
@@ -213,6 +238,17 @@ class Db():
         rec = self.new_record(parent, 0x8, stg.dbid, data)
         return rec
 
+    def dump_raw(self, root=3, depth=0):
+        rec = self.get_record_value(root)
+        val = hexlify(rec.value).decode()
+        if len(val) > 80:
+            val = val[:80] + '...'
+        print('%s%d (type %d) %s' % ('  '*depth, rec.dbid, rec.type, val))
+
+        rec = self.get_record_children(root)
+        for c in rec.children:
+            self.dump_raw(c['dbid'], depth+1)
+
     def dump_all(self):
         stg = self.get_user_storage(name='StgWindsor')
         usrs = [self.get_user(u['dbid']) for u in stg.users]
diff --git a/validitysensor/flash.py b/validitysensor/flash.py
index ce4dad8..6c00ea9 100644
--- a/validitysensor/flash.py
+++ b/validitysensor/flash.py
@@ -91,13 +91,19 @@ def get_fw_info(partition):
 def write_enable():
     assert_status(tls.cmd(db_write_enable))
 
-def flush_changes():
-    assert_status(tls.cmd(b'\x1a'))
+def call_cleanups():
+    rsp = tls.cmd(b'\x1a')
+    err = unpack('<H', rsp[:2])[0]
+    if err == 0x0491: # Nothing to commit
+        return # don't throw an exception, just ignore
+    assert_status(rsp)
 
 def erase_flash(partition):
     assert_status(tls.cmd(db_write_enable))
-    assert_status(tls.cmd(pack('<BB', 0x3f, partition)))
-    flush_changes()
+    try:
+        assert_status(tls.cmd(pack('<BB', 0x3f, partition)))
+    finally:
+        call_cleanups()
 
 def read_flash(partition, addr, size):
     cmd = pack('<BBBHLL', 0x40, partition, 1, 0, addr, size)
@@ -110,9 +116,11 @@ def read_flash(partition, addr, size):
 def write_flash(partition, addr, buf):
     tls.cmd(db_write_enable)
     cmd = pack('<BBBHLL', 0x41, partition, 1, 0, addr, len(buf)) + buf
-    rsp = tls.cmd(cmd)
-    assert_status(rsp)
-    flush_changes()
+    try:
+        rsp = tls.cmd(cmd)
+        assert_status(rsp)
+    finally:
+        call_cleanups()
 
 def write_flash_all(partition, ptr, buf):
     bs = 0x1000
diff --git a/validitysensor/init_flash.py b/validitysensor/init_flash.py
index a83f213..09f6800 100644
--- a/validitysensor/init_flash.py
+++ b/validitysensor/init_flash.py
@@ -13,8 +13,8 @@ from cryptography.hazmat.backends import default_backend
 
 from .tls import tls, hs_key, crt_hardcoded
 from .usb import usb
-from .flash import write_flash, erase_flash, flush_changes, PartitionInfo, get_flash_info
-from .sensor import reboot
+from .flash import write_flash, erase_flash, call_cleanups, PartitionInfo, get_flash_info
+from .sensor import reboot, RomInfo
 from .util import assert_status, unhex
 from .blobs import reset_blob
 
@@ -121,13 +121,14 @@ def init_flash():
 
     partition_flash(info, flash_layout_hardcoded, client_public)
 
-    rsp=usb.cmd(unhex('01'))
-    assert_status(rsp)
-    # ^ get device info, contains firmware version which is needed to lookup pubkey for server cert validation
+    RomInfo.get()
+    # ^ TODO: use the firmware version which to lookup pubkey for server cert validation
 
-    rsp=usb.cmd(unhex('50'))
-    assert_status(rsp)
-    flush_changes()
+    try:
+        rsp=usb.cmd(unhex('50'))
+        assert_status(rsp)
+    finally:
+        call_cleanups()
 
     rsp=rsp[2:]
     l,=unpack('<L', rsp[:4])
diff --git a/validitysensor/sensor.py b/validitysensor/sensor.py
index 20f1112..c45e86d 100644
--- a/validitysensor/sensor.py
+++ b/validitysensor/sensor.py
@@ -3,10 +3,11 @@ from enum import Enum
 from hashlib import sha256
 import os.path
 import logging
+from usb import core as usb_core
 from .tls import tls
-from .usb import usb
+from .usb import usb, CancelledException
 from .db import db, subtype_to_string
-from .flash import write_enable, flush_changes, read_flash, erase_flash, write_flash_all, read_flash_all
+from .flash import write_enable, call_cleanups, read_flash, erase_flash, write_flash_all, read_flash_all
 from time import sleep
 from struct import pack, unpack
 from .table_types import SensorTypeInfo, SensorCaptureProg
@@ -190,14 +191,10 @@ class CaptureMode(Enum):
     IDENTIFY=2
     ENROLL=3
 
-class CancelledException(Exception):
-    pass
-
 class Sensor():
     calib_data=b''
 
     def open(self):
-        self.interrupt_cb = None
         self.device_info = identify_sensor()
 
         logging.info('Opening sensor: %s' % self.device_info.name)
@@ -625,58 +622,32 @@ class Sensor():
         self.save()
 
     def cancel(self):
-        cb=usb.interrupt_cb
-        if cb is not None:
-            cb(None)
+        usb.cancel = True
 
-    def capture(self, mode, complete_cb):
-        if usb.interrupt_cb is not None:
-            raise Exception('Wrong state for capture')
+    def capture(self, mode):
+        try:
+            assert_status(tls.app(self.build_cmd_02(mode)))
 
-        def next(cb):
-            if cb is None:
-                usb.interrupt_cb = None
-                return
-
-            def run(b):
-                try:
-                    if b is None:
-                        raise CancelledException()
-
-                    cb(b)
-                except Exception as e:
-                    usb.interrupt_cb = None
-                    tls.app(unhexlify('04')) # capture stop if still running, cleanup
-                    complete_cb(None, e)
-
-            usb.interrupt_cb = run
-
-
-        def wait_start(b):
+            # start
+            b = usb.wait_int()
             if b[0] != 0:
                 raise Exception('wait_start: Unexpected interrupt type %s' % hexlify(b).decode())
 
-            next(wait_finger)
-
-        def wait_finger(b):
-            if b[0] == 2:
-                next(wait_capture_complete)
-
-            # TODO: report status?
-
-        def wait_capture_complete(b):
-            if b[0] != 3:
-                raise Exception('wait_finger: Unexpected interrupt type %s' % hexlify(b).decode())
-
-            if b[2] & 4:
-                capture_complete()
-                return
+            # wait for finger
+            while True:
+                b = usb.wait_int()
+                if b[0] == 2:
+                    break;
             
-            # TODO: report status?
-
-        def capture_complete():
-            next(None)
+            # wait capture complete
+            while True:
+                b = usb.wait_int()
+                if b[0] != 3:
+                    raise Exception('Unexpected interrupt type %s' % hexlify(b).decode())
 
+                if b[2] & 4:
+                    break
+            
             res = get_prg_status2()
 
             assert_status(res)
@@ -693,88 +664,69 @@ class Sensor():
             if error != 0:
                 raise Exception('Scanning problem: %04x' % error)
 
-            complete_cb((x, y, w1, w2), None)
+            return (x, y, w1, w2)
 
-        next(wait_start)
+        finally:
+            tls.app(unhexlify('04')) # capture stop if still running, cleanup
 
-        assert_status(tls.app(self.build_cmd_02(mode)))
-
-    def enrollment_update_start(self, key, complete_cb):
-        if usb.interrupt_cb is not None:
-            raise Exception('Wrong state, sensor\'s busy')
-
-        def wait(b):
-            if b is None:
-                raise Exception('Cancelling while enrollment is being updated is not a good idea.')
-
-            usb.interrupt_cb = None
-            complete_cb(new_key, b)
-
-        usb.interrupt_cb = wait
 
+    def enrollment_update_start(self, key):
         rsp=tls.app(pack('<BLL', 0x68, key, 0))
         assert_status(rsp)
         new_key, = unpack('<L', rsp[2:])
 
+        usb.wait_int()
+
+        return new_key
+
+    def create_enrollment(self):
+        assert_status(tls.app(pack('<BL', 0x69, 1)))
+
     def enrollment_update_end(self):
         assert_status(tls.app(pack('<BL', 0x69, 0)))
 
     # Generates interrupt
     def enrollment_update(self, prev):
         write_enable()
-        rsp=tls.app(b'\x6b' + prev)
-        assert_status(rsp)
-        flush_changes()
+        try:
+            rsp=tls.app(b'\x6b' + prev)
+            assert_status(rsp)
+        finally:
+            call_cleanups()
 
         return rsp[2:]
 
-    def append_new_image(self, prev, complete_cb):
-        if usb.interrupt_cb is not None:
-            raise Exception('Wrong state, sensor\'s busy')
-
-        def finished(b):
-            res = self.enrollment_update(prev)
-
-            l, res = res[:2], res[2:]
-            l, = unpack('<H', l)
-            if l != len(res):
-                raise Exception('Response size does not match %d != %d', l, len(res))
-
-            magic_len = 0x38 # hardcoded in the DLL
-            template = header = tid = None
-
-            while len(res) > 0:
-                tag, l = unpack('<HH', res[:4])
-
-                if tag == 0:
-                    template = res[:magic_len+l]
-                elif tag == 1:
-                    header = res[magic_len:magic_len+l]
-                elif tag == 3:
-                    tid = res[magic_len:magic_len+l]
-                else:
-                    logging.warning('Ignoring unknown tag %x' % tag)
-                    
-                res=res[magic_len+l:]
-
-            return (header, template, tid)
-
-        def wait(b):
-            if b is None:
-                raise Exception('Cancelling while enrollment is being updated is not a good idea.')
-
-            usb.interrupt_cb = None
-
-            try:
-                complete_cb(finished(b), None)
-            except Exception as e:
-                complete_cb(None, e)
-
-        usb.interrupt_cb = wait
-
-        # Start the work. Interrupt will be generated when it is finished.
+    def append_new_image(self, prev):
         self.enrollment_update(prev)
         
+        usb.wait_int()
+
+        res = self.enrollment_update(prev)
+
+        l, res = res[:2], res[2:]
+        l, = unpack('<H', l)
+        if l != len(res):
+            raise Exception('Response size does not match %d != %d', l, len(res))
+
+        magic_len = 0x38 # hardcoded in the DLL
+        template = header = tid = None
+
+        while len(res) > 0:
+            tag, l = unpack('<HH', res[:4])
+
+            if tag == 0:
+                template = res[:magic_len+l]
+            elif tag == 1:
+                header = res[magic_len:magic_len+l]
+            elif tag == 3:
+                tid = res[magic_len:magic_len+l]
+            else:
+                logging.warning('Ignoring unknown tag %x' % tag)
+                
+            res=res[magic_len+l:]
+
+        return (header, template, tid)
+        
 
     def make_finger_data(self, subtype, template, tid):
         template = pack('<HH', 1, len(template)) + template
@@ -787,70 +739,51 @@ class Sensor():
 
         return tinfo
 
-    def enroll(self, identity, subtype, update_cb, complete_cb):
+    def enroll(self, identity, subtype, update_cb):
         def do_create_finger(final_template, tid):
+            tinfo = self.make_finger_data(subtype, final_template, tid)
+
+            usr=db.lookup_user(identity)
+            if usr == None:
+                usr = db.new_user(identity)
+            else:
+                usr = usr.dbid
+            
+            recid = db.new_finger(usr, tinfo)
+            usb.wait_int()
+
+            glow_end_scan()
+
+            return recid
+
+        key=0
+        template=b''
+        self.create_enrollment()
+        while True:
             try:
-                tinfo = self.make_finger_data(subtype, final_template, tid)
-
-                usr=db.lookup_user(identity)
-                if usr == None:
-                    usr = db.new_user(identity)
-                else:
-                    usr = usr.dbid
-                
-                recid = db.new_finger(usr, tinfo)
+                glow_start_scan()
+                self.capture(CaptureMode.ENROLL)
+                key = self.enrollment_update_start(key)
+                rsp = self.append_new_image(template)
+                header, template, tid = rsp
+                update_cb(header, None)
+                if tid:
+                    break
 
+            except usb_core.USBError as e:
+                raise e
+            except CancelledException as e:
                 glow_end_scan()
-
-                complete_cb(recid, None)
+                raise e
             except Exception as e:
-                complete_cb(None, e)
+                print(e)
+                update_cb(None, e)
+                # sleep, so we don't end up in a busy loop spaming the sensor with requests in case of unrecoverable error
+            finally:
+                self.enrollment_update_end()
 
-
-        def start_iteration(key=0, template=b''):
-            def wrap_cb(f):
-                def r(res, ex):
-                    try:
-                        f(res, ex)
-                    except CancelledException as e:
-                        glow_end_scan()
-                        complete_cb(None, e)
-                    except Exception as e:
-                        update_cb(None, e)
-                        # sleep, so we don't end up in a busy loop spaming the sensor with requests in case of unrecoverable error
-                        sleep(1)
-                        self.enrollment_update_end()
-                        start_iteration(key, template)
-
-                return r
-
-            def capture_cb(res, e):
-                if e is not None: raise e
-                def enrollment_update_start_cb(new_key, b):
-                    def append_new_image_cb(rsp, e):
-                        if e is not None: raise e
-
-                        self.enrollment_update_end()
-
-                        header, new_template, tid = rsp
-                        update_cb(header, None)
-
-                        if tid:
-                            do_create_finger(new_template, tid)
-                        else:
-                            start_iteration(new_key, new_template)
-                    ## end of append_new_image_cb
-
-                    self.append_new_image(template, wrap_cb(append_new_image_cb))
-                ## end of enrollment_update_start_cb
-
-                self.enrollment_update_start(key, wrap_cb(enrollment_update_start_cb))
-            ## end of capture_cb
-
-            glow_start_scan()
-            self.capture(CaptureMode.ENROLL, wrap_cb(capture_cb))
-
-        start_iteration()
+        self.enrollment_update_end() # done twice for some reason
+        return do_create_finger(template, tid)
 
     def parse_dict(self, x):
         rc={}
@@ -861,74 +794,56 @@ class Sensor():
 
         return rc
 
-    def match_finger(self, complete_cb):
-        if usb.interrupt_cb is not None:
-            raise Exception('Wrong state for capture')
+    def match_finger(self):
+        try:
+            stg_id=0 # match against any storage
+            usr_id=0 # match against any user
+            cmd=pack('<BBBHHHHH', 0x5e, 2, 0xff, stg_id, usr_id, 1, 0,0)
+            rsp=tls.app(cmd)
+            assert_status(rsp)
 
-        def wait(b):
-            if b is None:
-                raise Exception('Cancelling while finger match is running is not a good idea.')
+            b = usb.wait_int()
+            if b[0] != 3:
+                raise Exception('Finger not recognized: %s' % hexlify(b).decode())
 
-            try:
-                if b[0] != 3:
-                    raise Exception('Finger not recognized: %s' % hexlify(b).decode())
+            # get results
+            rsp = tls.app(unhexlify('6000000000'))
+            assert_status(rsp)
+            rsp = rsp[2:]
 
-                # get results
-                rsp = tls.app(unhexlify('6000000000'))
-                assert_status(rsp)
-                rsp = rsp[2:]
+            (l,), rsp = unpack('<H', rsp[:2]), rsp[2:]
+            if l != len(rsp):
+                raise Exception('Response size does not match')
 
-                (l,), rsp = unpack('<H', rsp[:2]), rsp[2:]
-                if l != len(rsp):
-                    raise Exception('Response size does not match')
+            rsp=self.parse_dict(rsp)
 
-                rsp=self.parse_dict(rsp)
+            usrid, subtype, hsh = rsp[1], rsp[3], rsp[4]
+            usrid, = unpack('<L', usrid)
+            subtype, = unpack('<H', subtype)
 
-                usrid, subtype, hsh = rsp[1], rsp[3], rsp[4]
-                usrid, = unpack('<L', usrid)
-                subtype, = unpack('<H', subtype)
-
-                complete_cb((usrid, subtype, hsh), None)
-            except Exception as e:
-                complete_cb(None, e)
-            finally:
-                usb.interrupt_cb = None
-                # cleanup, ignore any errors
-                tls.app(unhexlify('6200000000'))
-
-        usb.interrupt_cb = wait
-
-        stg_id=0 # match against any storage
-        usr_id=0 # match against any user
-        cmd=pack('<BBBHHHHH', 0x5e, 2, 0xff, stg_id, usr_id, 1, 0,0)
-        rsp=tls.app(cmd)
-        assert_status(rsp)
+            return (usrid, subtype, hsh)
+        finally:
+            # cleanup, ignore any errors
+            tls.app(unhexlify('6200000000'))
 
         
-    def identify(self, update_cb, complete_cb):
-        def start():
+    def identify(self, update_cb):
+        while True:
             try:
                 glow_start_scan()
-                self.capture(CaptureMode.IDENTIFY, capture_cb)
-            except Exception as e:
-                # failed to start the capture, pointless to retry
-                glow_end_scan()
-                complete_cb(None, e)
-
-        def capture_cb(_, e):
-            try:
-                if e is not None: raise e
-                self.match_finger(complete_cb)
+                self.capture(CaptureMode.IDENTIFY)
+                break
+            except usb_core.USBError as e:
+                raise e
             except CancelledException as e:
                 glow_end_scan()
-                complete_cb(None, e)
+                raise e
             except Exception as e:
                 # Capture failed, retry
                 update_cb(e)
                 sleep(1)
-                start()
 
-        start()
+        return self.match_finger()
 
     def get_finger_blobs(self, usrid, subtype):
         usr = db.get_user(usrid)
diff --git a/validitysensor/upload_fwext.py b/validitysensor/upload_fwext.py
index 24d1b28..da8dca3 100644
--- a/validitysensor/upload_fwext.py
+++ b/validitysensor/upload_fwext.py
@@ -7,7 +7,7 @@ from os.path import basename
 from .tls import tls
 from .usb import usb
 from .sensor import reboot, write_hw_reg32, read_hw_reg32, identify_sensor
-from .flash import flush_changes, read_flash, erase_flash, write_flash_all, write_fw_signature, get_fw_info
+from .flash import read_flash, erase_flash, write_flash_all, write_fw_signature, get_fw_info
 from .util import assert_status
 
 firmware_home='/usr/share/python-validity'
@@ -55,7 +55,6 @@ def upload_fwext(fw_path=None):
     fwext=fwext[fwext.index(b'\x1a')+1:]
     fwext, signature = fwext[:-0x100], fwext[-0x100:]
 
-    #flush_changes()
     write_flash_all(2, 0, fwext)
     write_fw_signature(2, signature)
 
diff --git a/validitysensor/usb.py b/validitysensor/usb.py
index 8671e02..25af2be 100644
--- a/validitysensor/usb.py
+++ b/validitysensor/usb.py
@@ -1,5 +1,6 @@
 
 import logging
+import errno
 import usb.core as ucore
 from binascii import *
 from .util import assert_status, unhex
@@ -15,6 +16,8 @@ supported_devices=[
     (0x06cb, 0x009a),
 ]
 
+class CancelledException(Exception):
+    pass
 
 class Usb():
     def __init__(self):
@@ -22,6 +25,7 @@ class Usb():
         self.trace_enabled = False
         self.quit = None
         self.dev = None
+        self.cancel = False
 
     def open(self, vendor=None, product=None):
         if vendor is not None and product is not None:
@@ -48,9 +52,6 @@ class Usb():
 
         self.dev = dev
         self.dev.default_timeout = 15000
-        self.thread = Thread(target=lambda: self.int_thread())
-        self.thread.daemon = True
-        self.thread.start()
 
     def close(self):
         if self.dev is not None:
@@ -59,8 +60,6 @@ class Usb():
                 self.dev = None
             except:
                 pass
-            finally:
-                self.thread.join()
 
     def usb_dev(self):
         return self.dev
@@ -69,12 +68,12 @@ class Usb():
         #self.dev.set_configuration()
 
         # TODO analyse responses, detect hardware type
-        assert_status(self.cmd(unhexlify('01')))
+        assert_status(self.cmd(unhexlify('01'))) # RomInfo.get()
         assert_status(self.cmd(unhexlify('19')))
 
         # 43 -- get partition header(?) (02 -- fwext partition)
         # c28c745a in response is a FwextBuildtime = 0x5A748CC2
-        rsp=self.cmd(unhexlify('4302'))
+        rsp=self.cmd(unhexlify('4302')) # get_fw_info()
 
         assert_status(self.cmd(init_hardcoded))
         
@@ -106,6 +105,27 @@ class Usb():
             self.trace('<130< Error: %s' % repr(e))
             return None
 
+    # FIXME There is a chance of a race condition here
+    def cancel(self):
+        self.cancel = True
+
+    def wait_int(self):
+        self.cancel = False
+
+        while True:
+            try:
+                resp = self.dev.read(131, 1024, timeout=100)
+                resp = bytes(resp)
+                self.trace('<int< %s' % hexlify(resp).decode())
+                return resp
+            except USBError as e:
+                if e.errno == errno.ETIMEDOUT:
+                    if self.cancel:
+                        raise CancelledException()
+                else:
+                    raise e
+                
+
     def int_thread(self):
         try:
             while True:
diff --git a/validitysensor/util.py b/validitysensor/util.py
index f19131b..68fc936 100644
--- a/validitysensor/util.py
+++ b/validitysensor/util.py
@@ -6,8 +6,12 @@ from binascii import unhexlify
 def assert_status(b):
     s,=unpack('<H', b[:2])
     if s != 0:
+        if s == 0x44f:
+            raise Exception('Signature validation failed: %04x' % s)
+
         raise Exception('Failed: %04x' % s)
 
+
 def unhex(x):
     return unhexlify(re.sub('\W', '', x))