This is a preview version of the DisplayLink DL-7450 Software Development Kit Documentation. The functionality that is described and made available in this version is subject to addition, removal or change without warning.

`time` – time related functions

The time module provides functions for getting the current time and date, measuring time intervals, and for delays.

This verison of Python uses the standard POSIX systems epoch of 1970-01-01 00:00:00 UTC.

The DL-7450 uses the Network Time Protocol (NTP) to set the system time.

Functions

time.gmtime([secs])

time.localtime([secs])

Convert the time secs expressed in seconds since the Epoch (see above) into an 8-tuple which contains: (year, month, mday, hour, minute, second, weekday, yearday) If secs is not provided or None, then the current time from the RTC is used.

The gmtime() function returns a date-time tuple in UTC, and localtime() returns a date-time tuple in local time.

The format of the entries in the 8-tuple are:

year includes the century (for example 2014).
month is 1-12
mday is 1-31
hour is 0-23
minute is 0-59
second is 0-59
weekday is 0-6 for Mon-Sun
yearday is 1-366

time.mktime(): This is inverse function of localtime. It’s argument is a full 8-tuple which expresses a time as per localtime. It returns an integer which is the number of seconds since Jan 1, 2000.

time.sleep(seconds): Sleep for the given number of seconds. Some boards may accept seconds as a floating-point number to sleep for a fractional number of seconds. Note that other boards may not accept a floating-point argument, for compatibility with them use sleep_ms() and sleep_us() functions.

time.sleep_ms(ms)

Delay for given number of milliseconds, should be positive or 0.

This function will delay for at least the given number of milliseconds, but may take longer than that if other processing must take place, for example interrupt handlers or other threads. Passing in 0 for ms will still allow other processing to occur. Use sleep_us() for more precise delays.

time.sleep_us(us)

Delay for given number of microseconds, should be positive or 0.

This function attempts to provide an accurate delay of at least us microseconds, but it may take longer if the system has other higher priority processing to perform.

time.ticks_ms()

Returns an increasing millisecond counter with an arbitrary reference point, that wraps around after some value.

The wrap-around value is not explicitly exposed, but we will refer to it as TICKS_MAX to simplify discussion. Period of the values is TICKS_PERIOD = TICKS_MAX + 1. TICKS_PERIOD is guaranteed to be a power of two, but otherwise may differ from port to port. The same period value is used for all of ticks_ms(), ticks_us(), ticks_cpu() functions (for simplicity). Thus, these functions will return a value in range [0 .. TICKS_MAX], inclusive, total TICKS_PERIOD values. Note that only non-negative values are used. For the most part, you should treat values returned by these functions as opaque. The only operations available for them are ticks_diff() and ticks_add() functions described below.

Note: Performing standard mathematical operations (+, -) or relational operators (<, <=, >, >=) directly on these value will lead to invalid result. Performing mathematical operations and then passing their results as arguments to ticks_diff() or ticks_add() will also lead to invalid results from the latter functions.

time.ticks_us(): Just like ticks_ms() above, but in microseconds.

time.ticks_cpu(): Similar to ticks_ms() and ticks_us(), but with the highest possible resolution in the system. This function is intended for very fine benchmarking or very tight real-time loops.

time.ticks_add(ticks, delta)

Offset ticks by a given number, which can be either positive or negative. Given a ticks value, this function allows to calculate a ticks value delta ticks before or after it, following modular-arithmetic definition of tick values (see ticks_ms() above). ticks parameter must be a direct result of call to ticks_ms(), ticks_us(), or ticks_cpu() functions (or from previous call to ticks_add()). However, delta can be an arbitrary integer number or numeric expression. ticks_add() is useful for calculating deadlines for events/tasks. (Note: you must use ticks_diff() function to work with deadlines.)

Examples:

# Find out what ticks value there was 100ms ago
print(ticks_add(time.ticks_ms(), -100))

# Calculate deadline for operation and test for it
deadline = ticks_add(time.ticks_ms(), 200)
while ticks_diff(deadline, time.ticks_ms()) > 0:
    do_a_little_of_something()

# Find out TICKS_MAX used by this port
print(ticks_add(0, -1))

time.ticks_diff(ticks1, ticks2)

Measure ticks difference between values returned from ticks_ms(), ticks_us(), or ticks_cpu() functions, as a signed value which may wrap around.

The argument order is the same as for subtraction operator, ticks_diff(ticks1, ticks2) has the same meaning as ticks1 - ticks2. However, values returned by ticks_ms(), etc. functions may wrap around, so directly using subtraction on them will produce incorrect result. That is why ticks_diff() is needed, it implements modular (or more specifically, ring) arithmetic to produce correct result even for wrap-around values (as long as they not too distant in between, see below). The function returns a signed value in the range [-TICKS_PERIOD/2 .. TICKS_PERIOD/2-1] (that’s a typical range definition for two’s-complement signed binary integers). If the result is negative, it means that ticks1 occurred earlier in time than ticks2. Otherwise, it means that ticks1 occurred after ticks2. This holds only if ticks1 and ticks2 are apart from each other for no more than TICKS_PERIOD/2-1 ticks. If that does not hold, incorrect result will be returned. Specifically, if two tick values are apart for TICKS_PERIOD/2-1 ticks, that value will be returned by the function. However, if TICKS_PERIOD/2 of real-time ticks has passed between them, the function will return -TICKS_PERIOD/2 instead, i.e. result value will wrap around to the negative range of possible values.

ticks_diff() is designed to accommodate various usage patterns, among them:

Polling with timeout. In this case, the order of events is known, and you will deal only with positive results of ticks_diff():

# Wait for GPIO pin to be asserted, but at most 500us
start = time.ticks_us()
while pin.value() == 0:
    if time.ticks_diff(time.ticks_us(), start) > 500:
        raise TimeoutError

Scheduling events. In this case, ticks_diff() result may be negative if an event is overdue:

# This code snippet is not optimized
now = time.ticks_ms()
scheduled_time = task.scheduled_time()
if ticks_diff(scheduled_time, now) > 0:
    print("Too early, let's nap")
    sleep_ms(ticks_diff(scheduled_time, now))
    task.run()
elif ticks_diff(scheduled_time, now) == 0:
    print("Right at time!")
    task.run()
elif ticks_diff(scheduled_time, now) < 0:
    print("Oops, running late, tell task to run faster!")
    task.run(run_faster=true)

Note: Do not pass time() values to ticks_diff(), you should use normal mathematical operations on them. But note that time() may (and will) also overflow. This is known as https://en.wikipedia.org/wiki/Year_2038_problem.

time.time(): Returns the number of seconds, as an integer, since the Epoch.

Difference to CPython

In CPython, this function returns the number of seconds since Unix epoch, 1970-01-01 00:00 UTC, as a floating-point.

time.time_ns(): Similar to time() but returns nanoseconds since the Epoch, as an integer.

time.strftime(fmt_string[, time_tuple]): Create a readable string from the time. The fmt_string is compatible with the C Python strfmt function. The second parameter is a time-tuple, as returned by time.localtime or time.gmtime. If this parameter is omitted, then the current time is used.

time – time related functions

Functions

`time` – time related functions