bulk_sensor: New file with helper code for reading bulk sensors

Move the ClockSyncRegression class from adxl345.py to a new
bulk_sensors.py file.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/bulk_sensor.py

@@ -0,0 +1,53 @@
+# Tools for reading bulk sensor data from the mcu
+#
+# Copyright (C) 2020-2023  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+
+# Helper class for chip clock synchronization via linear regression
+class ClockSyncRegression:
+    def __init__(self, mcu, chip_clock_smooth, decay = 1. / 20.):
+        self.mcu = mcu
+        self.chip_clock_smooth = chip_clock_smooth
+        self.decay = decay
+        self.last_chip_clock = self.last_exp_mcu_clock = 0.
+        self.mcu_clock_avg = self.mcu_clock_variance = 0.
+        self.chip_clock_avg = self.chip_clock_covariance = 0.
+    def reset(self, mcu_clock, chip_clock):
+        self.mcu_clock_avg = self.last_mcu_clock = mcu_clock
+        self.chip_clock_avg = chip_clock
+        self.mcu_clock_variance = self.chip_clock_covariance = 0.
+        self.last_chip_clock = self.last_exp_mcu_clock = 0.
+    def update(self, mcu_clock, chip_clock):
+        # Update linear regression
+        decay = self.decay
+        diff_mcu_clock = mcu_clock - self.mcu_clock_avg
+        self.mcu_clock_avg += decay * diff_mcu_clock
+        self.mcu_clock_variance = (1. - decay) * (
+            self.mcu_clock_variance + diff_mcu_clock**2 * decay)
+        diff_chip_clock = chip_clock - self.chip_clock_avg
+        self.chip_clock_avg += decay * diff_chip_clock
+        self.chip_clock_covariance = (1. - decay) * (
+            self.chip_clock_covariance + diff_mcu_clock*diff_chip_clock*decay)
+    def set_last_chip_clock(self, chip_clock):
+        base_mcu, base_chip, inv_cfreq = self.get_clock_translation()
+        self.last_chip_clock = chip_clock
+        self.last_exp_mcu_clock = base_mcu + (chip_clock-base_chip) * inv_cfreq
+    def get_clock_translation(self):
+        inv_chip_freq = self.mcu_clock_variance / self.chip_clock_covariance
+        if not self.last_chip_clock:
+            return self.mcu_clock_avg, self.chip_clock_avg, inv_chip_freq
+        # Find mcu clock associated with future chip_clock
+        s_chip_clock = self.last_chip_clock + self.chip_clock_smooth
+        scdiff = s_chip_clock - self.chip_clock_avg
+        s_mcu_clock = self.mcu_clock_avg + scdiff * inv_chip_freq
+        # Calculate frequency to converge at future point
+        mdiff = s_mcu_clock - self.last_exp_mcu_clock
+        s_inv_chip_freq = mdiff / self.chip_clock_smooth
+        return self.last_exp_mcu_clock, self.last_chip_clock, s_inv_chip_freq
+    def get_time_translation(self):
+        base_mcu, base_chip, inv_cfreq = self.get_clock_translation()
+        clock_to_print_time = self.mcu.clock_to_print_time
+        base_time = clock_to_print_time(base_mcu)
+        inv_freq = clock_to_print_time(base_mcu + inv_cfreq) - base_time
+        return base_time, base_chip, inv_freq