Gabriel Staples Gabriel Staples - 3 months ago 34
Python Question

How to get millisecond and microsecond-resolution timestamps in Python

I finally figured this out and would like to share the knowledge and save someone a bunch of time, so see my answer below. However, I still need answers for Linux, so please answer if you know, as my code in my answer is for Windows only.

UPDATE: I've figured it out for Linux too, including for pre-Python 3.3 (ex: for the Raspberry Pi), and I've posted my new module/code in my answer below.

My original question: How do I get millisecond and microsecond-resolution timestamps in Python?
I'd also like the Arduino-like delay and delayMicroseconds() functions.

Answer

For Windows: Here's a fully-functional module for both Linux (works with pre-Python 3.3 too) and Windows:

Functions and code samples.
Functions include:

  • micros()
  • millis()
  • delay()
  • delayMicroseconds()

Python code module:

"""
GS_timing.py
-create some low-level Arduino-like millis() (milliseconds) and micros() 
 (microseconds) timing functions for Python 
By Gabriel Staples
http://www.ElectricRCAircraftGuy.com 
-click "Contact me" at the top of my website to find my email address 
Started: 11 July 2016 
Updated: 13 Aug 2016 

History (newest on top): 
20160813 - v0.2.0 created - added Linux compatibility, using ctypes, so that it's compatible with pre-Python 3.3 (for Python 3.3 or later just use the built-in time functions for Linux, shown here: https://docs.python.org/3/library/time.html)
-ex: time.clock_gettime(time.CLOCK_MONOTONIC_RAW)
20160711 - v0.1.0 created - functions work for Windows *only* (via the QPC timer)

References:
WINDOWS:
-personal (C++ code): GS_PCArduino.h
1) Acquiring high-resolution time stamps (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx
2) QueryPerformanceCounter function (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/ms644904(v=vs.85).aspx
3) QueryPerformanceFrequency function (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx
4) LARGE_INTEGER union (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/aa383713(v=vs.85).aspx

-*****http://stackoverflow.com/questions/4430227/python-on-win32-how-to-get-
absolute-timing-cpu-cycle-count

LINUX:
-http://stackoverflow.com/questions/1205722/how-do-i-get-monotonic-time-durations-in-python


"""

import ctypes, os 

#Constants:
VERSION = '0.2.0'

#-------------------------------------------------------------------
#FUNCTIONS:
#-------------------------------------------------------------------
#OS-specific low-level timing functions:
if (os.name=='nt'): #for Windows:
    def micros():
        "return a timestamp in microseconds (us)"
        tics = ctypes.c_int64()
        freq = ctypes.c_int64()

        #get ticks on the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceCounter(ctypes.byref(tics)) 
        #get the actual freq. of the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceFrequency(ctypes.byref(freq))  

        t_us = tics.value*1e6/freq.value
        return t_us

    def millis():
        "return a timestamp in milliseconds (ms)"
        tics = ctypes.c_int64()
        freq = ctypes.c_int64()

        #get ticks on the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceCounter(ctypes.byref(tics)) 
        #get the actual freq. of the internal ~2MHz QPC clock 
        ctypes.windll.Kernel32.QueryPerformanceFrequency(ctypes.byref(freq)) 

        t_ms = tics.value*1e3/freq.value
        return t_ms

elif (os.name=='posix'): #for Linux:

    #Constants:
    CLOCK_MONOTONIC_RAW = 4 # see <linux/time.h> here: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time.h

    #prepare ctype timespec structure of {long, long}
    class timespec(ctypes.Structure):
        _fields_ =\
        [
            ('tv_sec', ctypes.c_long),
            ('tv_nsec', ctypes.c_long)
        ]

    #Configure Python access to the clock_gettime C library, via ctypes:
    #Documentation:
    #-ctypes.CDLL: https://docs.python.org/3.2/library/ctypes.html
    #-librt.so.1 with clock_gettime: https://docs.oracle.com/cd/E36784_01/html/E36873/librt-3lib.html #-
    #-Linux clock_gettime(): http://linux.die.net/man/3/clock_gettime
    librt = ctypes.CDLL('librt.so.1', use_errno=True)
    clock_gettime = librt.clock_gettime
    #specify input arguments and types to the C clock_gettime() function
    # (int clock_ID, timespec* t)
    clock_gettime.argtypes = [ctypes.c_int, ctypes.POINTER(timespec)]

    def monotonic_time():
        "return a timestamp in seconds (sec)"
        t = timespec()
        #(Note that clock_gettime() returns 0 for success, or -1 for failure, in
        # which case errno is set appropriately)
        #-see here: http://linux.die.net/man/3/clock_gettime
        if clock_gettime(CLOCK_MONOTONIC_RAW , ctypes.pointer(t)) != 0:
            #if clock_gettime() returns an error
            errno_ = ctypes.get_errno()
            raise OSError(errno_, os.strerror(errno_))
        return t.tv_sec + t.tv_nsec*1e-9 #sec 

    def micros():
        "return a timestamp in microseconds (us)"
        return monotonic_time()*1e6 #us 

    def millis():
        "return a timestamp in milliseconds (ms)"
        return monotonic_time()*1e3 #ms 

#Other timing functions:
def delay(delay_ms):
    "delay for delay_ms milliseconds (ms)"
    t_start = millis()
    while (millis() - t_start < delay_ms):
      pass #do nothing 
    return

def delayMicroseconds(delay_us):
    "delay for delay_us microseconds (us)"
    t_start = micros()
    while (micros() - t_start < delay_us):
      pass #do nothing 
    return 

#-------------------------------------------------------------------
#EXAMPLES:
#-------------------------------------------------------------------
#Only executute this block of code if running this module directly,
#*not* if importing it
#-see here: http://effbot.org/pyfaq/tutor-what-is-if-name-main-for.htm
if __name__ == "__main__": #if running this module as a stand-alone program

    #print loop execution time 100 times, using micros()
    tStart = micros() #us
    for x in range(0, 100):
        tNow = micros() #us
        dt = tNow - tStart #us; delta time 
        tStart = tNow #us; update 
        print("dt(us) = " + str(dt))

    #print loop execution time 100 times, using millis()
    print("\n")
    tStart = millis() #ms
    for x in range(0, 100):
        tNow = millis() #ms
        dt = tNow - tStart #ms; delta time 
        tStart = tNow #ms; update 
        print("dt(ms) = " + str(dt))

    #print a counter once per second, for 5 seconds, using delay 
    print("\nstart")
    for i in range(1,6):
        delay(1000)
        print(i)

    #print a counter once per second, for 5 seconds, using delayMicroseconds
    print("\nstart")
    for i in range(1,6):
        delayMicroseconds(1000000)
        print(i)

If you know how to get the above millisecond and microsecond-resolution timestamps in Linux, please post, as that would be very helpful too.

This works for Linux too, including in pre-Python 3.3, since I'm using C functions via the ctypes module in order to read the time stamps.

(Note: code above originally posted here: http://www.electricrcaircraftguy.com/2016/07/arduino-like-millisecond-and-microsecond-timestamps-in-python.html)

Special thanks to @ArminRonacher for his brilliant pre-Python 3.3 Linux answer here: http://stackoverflow.com/a/1205762/4561887


Update: prior to Python 3.3, the built-in Python time library (https://docs.python.org/3.5/library/time.html) didn't have any explicitly high-resolution functions. Now, however it does provide other options, including some high-resolution functions.

My module above, however, provides high-resolution timestamps for Python code before Python 3.3, as well as after, and it does so on both Linux and Windows.

Here's an example of what I mean, showing that the time.sleep() function is NOT necessarily a high-resolution function. On my Windows machine, it's resolution is perhaps 8ms at best, whereas my module above has 0.5us resolution on the same machine.

Code demonstration:

import time
import GS_timing as timing

def delayMicroseconds(n):
    time.sleep(n / 1000000.)

def delayMillisecond(n):
    time.sleep(n / 1000.)

t_start = 0
t_end = 0

#using time.sleep
print('using time.sleep')
print('delayMicroseconds(1)')
for x in range(10):
    t_start = timing.micros() #us 
    delayMicroseconds(1)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))
print('delayMicroseconds(2000)')
for x in range(10):
    t_start = timing.micros() #us 
    delayMicroseconds(2000)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))

#using GS_timing
print('\nusing GS_timing')
print('timing.delayMicroseconds(1)')
for x in range(10):
    t_start = timing.micros() #us 
    timing.delayMicroseconds(1)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))
print('timing.delayMicroseconds(2000)')
for x in range(10):
    t_start = timing.micros() #us 
    timing.delayMicroseconds(2000)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))

SAMPLE RESULTS ON MY WINDOWS 8.1 MACHINE (notice how much worse time.sleep does):

using time.sleep
delayMicroseconds(1)
dt (us) = 2872.059814453125
dt (us) = 886.3939208984375
dt (us) = 770.4649658203125
dt (us) = 1138.7698974609375
dt (us) = 1426.027099609375
dt (us) = 734.557861328125
dt (us) = 10617.233642578125
dt (us) = 9594.90576171875
dt (us) = 9155.299560546875
dt (us) = 9520.526611328125
delayMicroseconds(2000)
dt (us) = 8799.3056640625
dt (us) = 9609.2685546875
dt (us) = 9679.5439453125
dt (us) = 9248.145263671875
dt (us) = 9389.721923828125
dt (us) = 9637.994262695312
dt (us) = 9616.450073242188
dt (us) = 9592.853881835938
dt (us) = 9465.639892578125
dt (us) = 7650.276611328125

using GS_timing
timing.delayMicroseconds(1)
dt (us) = 53.3477783203125
dt (us) = 36.93310546875
dt (us) = 36.9329833984375
dt (us) = 34.8812255859375
dt (us) = 35.3941650390625
dt (us) = 40.010986328125
dt (us) = 38.4720458984375
dt (us) = 56.425537109375
dt (us) = 35.9072265625
dt (us) = 36.420166015625
timing.delayMicroseconds(2000)
dt (us) = 2039.526611328125
dt (us) = 2046.195068359375
dt (us) = 2033.8841552734375
dt (us) = 2037.4747314453125
dt (us) = 2032.34521484375
dt (us) = 2086.2059326171875
dt (us) = 2035.4229736328125
dt (us) = 2051.32470703125
dt (us) = 2040.03955078125
dt (us) = 2027.215576171875

SAMPLE RESULTS ON MY RASPBERRY PI VERSION 1 B+ (notice that the results between using time.sleep and my module are basically identical...apparently the low-level functions in time are already accessing better-resolution timers here, since it's a Linux machine (running Raspbian)...BUT in my GS_timing module I am explicitly calling the CLOCK_MONOTONIC_RAW timer. Who knows what's being used otherwise):

using time.sleep
delayMicroseconds(1)
dt (us) = 1022.0
dt (us) = 417.0
dt (us) = 407.0
dt (us) = 450.0
dt (us) = 2078.0
dt (us) = 393.0
dt (us) = 1297.0
dt (us) = 878.0
dt (us) = 1135.0
dt (us) = 2896.0
delayMicroseconds(2000)
dt (us) = 2746.0
dt (us) = 2568.0
dt (us) = 2512.0
dt (us) = 2423.0
dt (us) = 2454.0
dt (us) = 2608.0
dt (us) = 2518.0
dt (us) = 2569.0
dt (us) = 2548.0
dt (us) = 2496.0

using GS_timing
timing.delayMicroseconds(1)
dt (us) = 572.0
dt (us) = 673.0
dt (us) = 1084.0
dt (us) = 561.0
dt (us) = 728.0
dt (us) = 576.0
dt (us) = 556.0
dt (us) = 584.0
dt (us) = 576.0
dt (us) = 578.0
timing.delayMicroseconds(2000)
dt (us) = 2741.0
dt (us) = 2466.0
dt (us) = 2522.0
dt (us) = 2810.0
dt (us) = 2589.0
dt (us) = 2681.0
dt (us) = 2546.0
dt (us) = 3090.0
dt (us) = 2600.0
dt (us) = 2400.0