sos_filter: define filtfilt call

To implement host-side analysis of tap data,
we need a way to apply the same filtering as on the mcu.
As bonus, it cancels the induced signal delay.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

Author: nefelim4ag

klippy/extras/trigger_analog.py

@@ -38,6 +38,7 @@ def __init__(self, sps, cfg_error, highpass=None, highpass_order=1,
             return
         try:
             import scipy.signal as signal
+            import numpy
         except:
             raise cfg_error("DigitalFilter require the SciPy module")
         if highpass:
@@ -69,6 +70,12 @@ def get_filter_sections(self):
     def get_initial_state(self):
         return self.initial_state
 
+    def filtfilt(self, data):
+        import scipy.signal as signal
+        import numpy
+        data = numpy.array(data)
+        return signal.sosfiltfilt(self.filter_sections, data)
+
 # Produce sample to sample difference (derivative) of a DigitalFilter
 class DerivativeFilter:
     def __init__(self, main_filter):