tools: added mavfixtimedrift.py

this fixes TimeUS in logs for clock drift from bad crystals on some
flight controllers

tools/mavfixtimedrift.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python
+
+'''
+fix time drift in the TimeUS field of logs based on GPS time
+this helps when post-processing a log for a time sensitive task for flight
+controllers with very bad crystals
+it assumes constant drift
+'''
+
+import os
+import sys
+from argparse import ArgumentParser
+from progress.bar import Bar
+import time
+import struct
+
+parser = ArgumentParser(description=__doc__)
+
+parser.add_argument("log_in")
+parser.add_argument("log_out")
+parser.add_argument("--fix", action='store_true', default=False)
+
+args = parser.parse_args()
+
+from pymavlink import mavutil
+from pymavlink import DFReader
+
+log1 = mavutil.mavlink_connection(args.log_in)
+
+if not isinstance(log1,DFReader.DFReader_binary):
+    print("Must be a bin log")
+    sys.exit(1)
+
+gps_id = log1.name_to_id.get('GPS', None)
+if gps_id is None:
+    print("No GPS messages")
+    sys.exit(1)
+
+print("Finding drift")
+first_gps_msg = None
+last_gps_msg = None
+
+while True:
+    m = log1.recv_match(type='GPS')
+    if m is None:
+        break
+    if m.I != 0 or m.Status < 3:
+        continue
+    if first_gps_msg is None:
+        first_gps_msg = m
+    last_gps_msg = m
+
+if first_gps_msg is None:
+    print("No GPS[0] messages")
+    sys.exit(1)
+
+dt1 = (last_gps_msg.GWk*7*24*3600 + last_gps_msg.GMS*0.001) - (first_gps_msg.GWk*7*24*3600 + first_gps_msg.GMS*0.001)
+dt2 = (last_gps_msg.TimeUS - first_gps_msg.TimeUS) * 1.0e-6
+
+PPM = 1.0e6*(dt2-dt1)/dt1
+
+print("Drift is %.2f seconds, %.1f PPM" % ((dt2-dt1), PPM))
+
+if not args.fix:
+    print("--fix not specified, just reporting")
+    sys.exit(0)
+
+if abs(PPM) < 10:
+    print("Not enough drift to fix")
+    sys.exit(1)
+
+log1.rewind()
+
+TimeUS_start = first_gps_msg.TimeUS
+
+output = open(args.log_out, mode='wb')
+
+def write_message(m):
+    mtype = m.get_type()
+    buf = bytearray(m.get_msgbuf())
+    if hasattr(m,'TimeUS'):
+        dt = (m.TimeUS - TimeUS_start)*1.0e-6
+        new_TimeUS = m.TimeUS - (dt * PPM)
+        if new_TimeUS < 0:
+            return
+        timeus_buf = struct.pack("Q",int(new_TimeUS))
+        buf = buf[:3] + timeus_buf + buf[11:]
+    output.write(buf)
+
+bar = Bar('Processing log', max=100)
+
+now = time.time()
+
+print("Processing log")
+
+pct = 0
+
+while True:
+    m = log1.recv_msg()
+    if m is None:
+        break
+    write_message(m)
+    new_pct = (log1.offset * 100) // log1.data_len
+    if new_pct != pct:
+        bar.next()
+        pct = new_pct
+
+print("\nDone")