def read(self, piconet): """ Reads Bluetooth clock. If piconet is True, reads piconet clock. If False, reads native clock (which is the same as piconet clock if local BT is piconet master). Returns a tuple with BT clock and accuracy, or None if not successful. Accuracy may be zero (means theoretical infinit precision). Unit is Bluetooth "ticks" (312.5 us each), wraps 32 bits """ addr = None if piconet: addr = self.addr # FIXME handle temporary failure return mcap_sock.hci_read_clock(self.raw_socket, addr)
def _determine_latency(self): """ Determine how much time it takes to read HCI clock """ # Exercise modules first mcap_sock.hci_read_clock(self.raw_socket, None) t = time.time() mcap_sock.hci_read_clock(self.raw_socket, None) t = time.time() mcap_sock.hci_read_clock(self.raw_socket, None) t = time.time() # take a bunch of measures latencies = [] latencies2 = [] for x in range(0, 20): t1 = time.time() # FIXME handle temporary failure mcap_sock.hci_read_clock(self.raw_socket, None) t2 = time.time() latency = t2 - t1 latencies.append(latency) latencies2.append(latency * latency) s = sum(latencies) n = len(latencies) avg = s / n stdev = math.sqrt((n * sum(latencies2) - s * s)) / n filtered = [] for latency in latencies: # leap of faith here: we assume that latencies too # high are result of preemption between calls if latency < avg + 6 * stdev: filtered.append(latency) # Return average without freak samples avg = sum(filtered) / len(filtered) return int(avg * 1000000)
def read_native(self): # FIXME handle temporary failure return mcap_sock.hci_read_clock(self.raw_socket, None)
