improve time stamp accuracy of the CAN messages for Kvaser and Vector buses on the Windows platform. (see hardbyte#934)

On Windows the value returned by time.time is refreshed at best every 0.5ms, and on some PCs the default refresh rate is every 10ms.

The idea is to get the value of time.perf_counter at the moment when time.time is refreshed and use this as a reference point.

Author: danielhrisca

can/interfaces/kvaser/canlib.py

@@ -13,6 +13,7 @@
 
 from can import CanError, BusABC
 from can import Message
+from can.util import time_perfcounter_correlation
 from . import constants as canstat
 from . import structures
 
@@ -491,12 +492,16 @@ def __init__(self, channel, can_filters=None, **kwargs):
         canBusOn(self._write_handle)
 
         timer = ctypes.c_uint(0)
+        ts, perfcounter = time_perfcounter_correlation()
         try:
             kvReadTimer(self._read_handle, ctypes.byref(timer))
+            current_perfcounter = time.perf_counter()
+            now = ts + (current_perfcounter - perfcounter)
+            self._timestamp_offset = now - (timer.value * TIMESTAMP_FACTOR)
         except Exception as exc:
             # timer is usually close to 0
             log.info(str(exc))
-        self._timestamp_offset = time.time() - (timer.value * TIMESTAMP_FACTOR)
+            self._timestamp_offset = time.time() - (timer.value * TIMESTAMP_FACTOR)
 
         self._is_filtered = False
         super().__init__(channel=channel, can_filters=can_filters, **kwargs)

can/interfaces/vector/canlib.py

@@ -32,7 +32,7 @@
 # Import Modules
 # ==============
 from can import BusABC, Message
-from can.util import len2dlc, dlc2len, deprecated_args_alias
+from can.util import len2dlc, dlc2len, deprecated_args_alias, time_perfcounter_correlation
 from .exceptions import VectorError
 
 # Define Module Logger
@@ -295,11 +295,14 @@ def __init__(
         # Calculate time offset for absolute timestamps
         offset = xlclass.XLuint64()
         try:
+            ts, perfcounter = time_perfcounter_correlation()
             try:
                 xldriver.xlGetSyncTime(self.port_handle, offset)
             except VectorError:
                 xldriver.xlGetChannelTime(self.port_handle, self.mask, offset)
-            self._time_offset = time.time() - offset.value * 1e-9
+            current_perfcounter = time.perf_counter()
+            now = ts + (current_perfcounter - perfcounter)
+            self._time_offset = now - offset.value * 1e-9
         except VectorError:
             self._time_offset = 0.0
 

can/util.py

@@ -4,6 +4,7 @@
 import functools
 import warnings
 from typing import Dict, Optional, Union
+from time import time, perf_counter
 
 from can import typechecking
 
@@ -325,6 +326,24 @@ def rename_kwargs(func_name, kwargs, aliases):
             else:
                 warnings.warn("{} is deprecated".format(alias), DeprecationWarning)
 
+def time_perfcounter_correlation():
+    """ on Windows platform this will help with the accuracy of using the time.time fucntion.
+
+    Returns
+    -------
+    t, performance_counter : (time.time, float)
+        time.time value and perf_counter value when the time.time is updated
+
+    """
+    if platform.system() == "Windows":
+        t0 = time()
+        while 1:
+            t1, performance_counter = time(), perf_counter()
+            if t1 != t0:
+                break
+    else:
+        return time(), perf_counter()
+    return t1, performance_counter
 
 if __name__ == "__main__":
     print("Searching for configuration named:")