diff --git a/klippy/extras/adxl345.py b/klippy/extras/adxl345.py
index 8868943d7..1c2838620 100644
--- a/klippy/extras/adxl345.py
+++ b/klippy/extras/adxl345.py
@@ -1,10 +1,10 @@
 # Support for reading acceleration data from an adxl345 chip
 #
-# Copyright (C) 2020  Kevin O'Connor <kevin@koconnor.net>
+# Copyright (C) 2020-2021  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
-import logging, time, collections, multiprocessing, os
-from . import bus
+import logging, time, collections, threading, multiprocessing, os
+from . import bus, motion_report
 
 # ADXL345 registers
 REG_DEVID = 0x00
@@ -30,24 +30,33 @@ Accel_Measurement = collections.namedtuple(
 
 # Helper class to obtain measurements
 class ADXL345QueryHelper:
-    def __init__(self, printer, chip, axes_map):
+    def __init__(self, printer, chip, cconn):
         self.printer = printer
         self.chip = chip
-        self.axes_map = axes_map
+        self.cconn = cconn
+        print_time = printer.lookup_object('toolhead').get_last_move_time()
+        self.request_start_time = self.request_end_time = print_time
         self.raw_samples = None
         self.samples = []
         self.drops = self.overflows = 0
+        self.start2_time = 0.
         self.time_per_sample = self.start_range = self.end_range = 0.
     def finish_measurements(self):
-        self.chip._finish_measurements()
+        toolhead = self.printer.lookup_object('toolhead')
+        self.request_end_time = toolhead.get_last_move_time()
+        toolhead.wait_moves()
+        self.cconn.finalize()
+        toolhead.dwell(0.200)
+        toolhead.wait_moves()
         self._setup_data(*self.chip.final_results) # XXX
     def get_stats(self):
         return ("drops=%d,overflows=%d"
                 ",time_per_sample=%.9f,start_range=%.6f,end_range=%.6f"
                 % (self.drops, self.overflows,
                    self.time_per_sample, self.start_range, self.end_range))
-    def _setup_data(self, raw_samples, end_sequence, overflows,
+    def _setup_data(self, end_sequence, overflows,
                     start1_time, start2_time, end1_time, end2_time):
+        raw_samples = self.cconn.get_messages()
         if not raw_samples or not end_sequence:
             return
         self.raw_samples = raw_samples
@@ -55,32 +64,26 @@ class ADXL345QueryHelper:
         self.start2_time = start2_time
         self.start_range = start2_time - start1_time
         self.end_range = end2_time - end1_time
-        self.total_count = (end_sequence - 1) * 8 + len(raw_samples[-1][1]) // 6
+        self.total_count = raw_samples[-1]['params']['data'][-1][0] + 1
         total_time = end2_time - start2_time
-        self.time_per_sample = time_per_sample = total_time / self.total_count
-        self.seq_to_time = time_per_sample * 8.
-        actual_count = sum([len(data)//6 for _, data in raw_samples])
+        self.time_per_sample = total_time / self.total_count
+        actual_count = sum([len(m['params']['data']) for m in raw_samples])
         self.drops = self.total_count - actual_count
     def decode_samples(self):
         if not self.raw_samples:
             return self.samples
-        (x_pos, x_scale), (y_pos, y_scale), (z_pos, z_scale) = self.axes_map
-        actual_count = 0
+        count = 0
         self.samples = samples = [None] * self.total_count
-        for seq, data in self.raw_samples:
-            d = bytearray(data)
-            count = len(data)
-            sdata = [(d[i] | (d[i+1] << 8)) - ((d[i+1] & 0x80) << 9)
-                     for i in range(0, count-1, 2)]
-            seq_time = self.start2_time + seq * self.seq_to_time
-            for i in range(count//6):
-                samp_time = seq_time + i * self.time_per_sample
-                x = sdata[i*3 + x_pos] * x_scale
-                y = sdata[i*3 + y_pos] * y_scale
-                z = sdata[i*3 + z_pos] * z_scale
-                samples[actual_count] = Accel_Measurement(samp_time, x, y, z)
-                actual_count += 1
-        del samples[actual_count:]
+        for msg in self.raw_samples:
+            for seq, x, y, z in msg['params']['data']:
+                samp_time = self.start2_time + seq * self.time_per_sample
+                if samp_time < self.request_start_time:
+                    continue
+                if samp_time > self.request_end_time:
+                    break
+                samples[count] = Accel_Measurement(samp_time, x, y, z)
+                count += 1
+        del samples[count:]
         return self.samples
     def write_to_file(self, filename):
         def write_impl():
@@ -180,13 +183,15 @@ class ADXLCommandHelper:
         val = gcmd.get("VAL", minval=0, maxval=255, parser=lambda x: int(x, 0))
         self.chip.set_reg(reg, val)
 
+MIN_MSG_TIME = 0.100
+
 # Printer class that controls ADXL345 chip
 class ADXL345:
     def __init__(self, config):
         self.printer = config.get_printer()
         ADXLCommandHelper(config, self)
         self.query_rate = 0
-        self.last_tx_time = 0.
+        self.last_sequence = 0
         am = {'x': (0, SCALE), 'y': (1, SCALE), 'z': (2, SCALE),
               '-x': (0, -SCALE), '-y': (1, -SCALE), '-z': (2, -SCALE)}
         axes_map = config.getlist('axes_map', ('x','y','z'), count=3)
@@ -197,8 +202,8 @@ class ADXL345:
         if self.data_rate not in QUERY_RATES:
             raise config.error("Invalid rate parameter: %d" % (self.data_rate,))
         # Measurement storage (accessed from background thread)
+        self.lock = threading.Lock()
         self.raw_samples = []
-        self.last_sequence = 0
         self.samples_start1 = self.samples_start2 = 0.
         # Setup mcu sensor_adxl345 bulk query code
         self.spi = bus.MCU_SPI_from_config(config, 3, default_speed=5000000)
@@ -212,6 +217,15 @@ class ADXL345:
         mcu.register_config_callback(self._build_config)
         mcu.register_response(self._handle_adxl345_start, "adxl345_start", oid)
         mcu.register_response(self._handle_adxl345_data, "adxl345_data", oid)
+        # API server endpoints
+        self.api_dump = motion_report.APIDumpHelper(
+            self.printer, self._api_update, self._api_startstop, 0.100)
+        self.name = "default"
+        if len(config.get_name().split()) > 1:
+            self.name = config.get_name().split()[1]
+        wh = self.printer.lookup_object('webhooks')
+        wh.register_mux_endpoint("adxl345/dump_adxl345", "sensor", self.name,
+                                 self._handle_dump_adxl345)
     def _build_config(self):
         self.query_adxl345_cmd = self.mcu.lookup_command(
             "query_adxl345 oid=%c clock=%u rest_ticks=%u",
@@ -223,20 +237,6 @@ class ADXL345:
             oid=self.oid, cq=self.spi.get_command_queue())
     def _clock_to_print_time(self, clock):
         return self.mcu.clock_to_print_time(self.mcu.clock32_to_clock64(clock))
-    def _handle_adxl345_start(self, params):
-        self.samples_start1 = self._clock_to_print_time(params['start1_clock'])
-        self.samples_start2 = self._clock_to_print_time(params['start2_clock'])
-    def _handle_adxl345_data(self, params):
-        last_sequence = self.last_sequence
-        sequence = (last_sequence & ~0xffff) | params['sequence']
-        if sequence < last_sequence:
-            sequence += 0x10000
-        self.last_sequence = sequence
-        raw_samples = self.raw_samples
-        if len(raw_samples) >= 300000:
-            # Avoid filling up memory with too many samples
-            return
-        raw_samples.append((sequence, params['data']))
     def _convert_sequence(self, sequence):
         sequence = (self.last_sequence & ~0xffff) | sequence
         if sequence < self.last_sequence:
@@ -255,8 +255,40 @@ class ADXL345:
                     "This is generally indicative of connection problems "
                     "(e.g. faulty wiring) or a faulty adxl345 chip." % (
                         reg, val, stored_val))
+    # Measurement collection
     def is_measuring(self):
         return self.query_rate > 0
+    def _handle_adxl345_start(self, params):
+        self.samples_start1 = self._clock_to_print_time(params['start1_clock'])
+        self.samples_start2 = self._clock_to_print_time(params['start2_clock'])
+    def _handle_adxl345_data(self, params):
+        with self.lock:
+            self.raw_samples.append(params)
+    def _extract_samples(self, raw_samples):
+        # Load variables to optimize inner loop below
+        (x_pos, x_scale), (y_pos, y_scale), (z_pos, z_scale) = self.axes_map
+        last_sequence = self.last_sequence
+        # Process every message in raw_samples
+        count = 0
+        samples = [None] * (len(raw_samples) * 8)
+        for params in raw_samples:
+            seq = (last_sequence & ~0xffff) | params['sequence']
+            if seq < last_sequence:
+                seq += 0x10000
+            last_sequence = seq
+            d = bytearray(params['data'])
+            len_d = len(d)
+            sdata = [(d[i] | (d[i+1] << 8)) - ((d[i+1] & 0x80) << 9)
+                     for i in range(0, len_d-1, 2)]
+            for i in range(len_d // 6):
+                x = round(sdata[i*3 + x_pos] * x_scale, 6)
+                y = round(sdata[i*3 + y_pos] * y_scale, 6)
+                z = round(sdata[i*3 + z_pos] * z_scale, 6)
+                samples[count] = (seq * 8 + i, x, y, z)
+                count += 1
+        self.last_sequence = last_sequence
+        del samples[count:]
+        return samples
     def _start_measurements(self):
         if self.is_measuring():
             return
@@ -267,54 +299,68 @@ class ADXL345:
             raise self.printer.command_error("Invalid adxl345 id (got %x vs %x)"
                                              % (dev_id, ADXL345_DEV_ID))
         # Setup chip in requested query rate
-        clock = 0
-        if self.last_tx_time:
-            clock = self.mcu.print_time_to_clock(self.last_tx_time)
-        self.set_reg(REG_POWER_CTL, 0x00, minclock=clock)
+        self.set_reg(REG_POWER_CTL, 0x00)
         self.set_reg(REG_DATA_FORMAT, 0x0B)
         self.set_reg(REG_FIFO_CTL, 0x00)
         self.set_reg(REG_BW_RATE, QUERY_RATES[self.data_rate])
         self.set_reg(REG_FIFO_CTL, 0x80)
         # Setup samples
-        print_time = self.printer.lookup_object('toolhead').get_last_move_time()
-        self.raw_samples = []
-        self.last_sequence = 0
+        systime = self.printer.get_reactor().monotonic()
+        print_time = self.mcu.estimated_print_time(systime) + MIN_MSG_TIME
         self.samples_start1 = self.samples_start2 = print_time
+        self.last_sequence = 0
+        with self.lock:
+            self.raw_samples = []
         # Start bulk reading
         reqclock = self.mcu.print_time_to_clock(print_time)
         rest_ticks = self.mcu.seconds_to_clock(4. / self.data_rate)
-        self.last_tx_time = print_time
         self.query_rate = self.data_rate
         self.query_adxl345_cmd.send([self.oid, reqclock, rest_ticks],
                                     reqclock=reqclock)
-        logging.info("ADXL345 starting measurements")
+        logging.info("ADXL345 starting '%s' measurements", self.name)
     def _finish_measurements(self):
         if not self.is_measuring():
             return
         # Halt bulk reading
-        print_time = self.printer.lookup_object('toolhead').get_last_move_time()
-        clock = self.mcu.print_time_to_clock(print_time)
-        params = self.query_adxl345_end_cmd.send([self.oid, 0, 0],
-                                                 minclock=clock)
-        self.last_tx_time = print_time
+        params = self.query_adxl345_end_cmd.send([self.oid, 0, 0])
         self.query_rate = 0
-        raw_samples = self.raw_samples
-        self.raw_samples = []
+        with self.lock:
+            self.raw_samples = []
         # Generate results
         end1_time = self._clock_to_print_time(params['end1_clock'])
         end2_time = self._clock_to_print_time(params['end2_clock'])
         end_sequence = self._convert_sequence(params['sequence'])
         overflows = params['limit_count']
-        logging.info("ADXL345 finished measurements")
-        self.final_results = (raw_samples, end_sequence, overflows,
+        logging.info("ADXL345 finished '%s' measurements", self.name)
+        self.final_results = (end_sequence, overflows,
                               self.samples_start1, self.samples_start2,
                               end1_time, end2_time) # XXX
+    # API interface
+    def _api_update(self, eventtime):
+        with self.lock:
+            raw_samples = self.raw_samples
+            self.raw_samples = []
+        if not raw_samples:
+            return {}
+        samples = self._extract_samples(raw_samples)
+        if not samples:
+            return {}
+        return {'data': samples}
+    def _api_startstop(self, is_start):
+        if is_start:
+            self._start_measurements()
+        else:
+            self._finish_measurements()
+    def _handle_dump_adxl345(self, web_request):
+        self.api_dump.add_client(web_request)
+        hdr = ('sequence', 'x_acceleration', 'y_acceleration', 'z_acceleration')
+        web_request.send({'header': hdr})
     def start_internal_client(self):
         if self.is_measuring():
             raise self.printer.command_error(
                 "ADXL345 measurement already in progress")
-        self._start_measurements()
-        return ADXL345QueryHelper(self.printer, self, self.axes_map)
+        cconn = self.api_dump.add_internal_client()
+        return ADXL345QueryHelper(self.printer, self, cconn)
 
 def load_config(config):
     return ADXL345(config)