`utime` – time related functions¶

This module implements a subset of the corresponding CPython module, as described below. For more information, refer to the original CPython documentation: time.

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

Time Epoch: The Unix port uses the POSIX standard epoch of 1970-01-01 00:00:00 UTC. However, all other ports use an epoch of 2000-01-01 00:00:00 UTC. The reason for the unconventional epoch is that, at least until 2034, the time fits into a 31-bit “small int” and thus a call to time.time() does not involve memory allocation.

Maintaining actual calendar date/time is port-dependent. * On operating systems, such as Unix, that manage time on their own

MicroPython simply makes the appropriate system calls to retrieve time and it cannot set the time.

On ports with an RTOS that can manage time, the Real Time Clock (RTC) is managed by the RTOS and MicroPython leverages the RTOS’ functionality to retrieve and set time. On those ports the machine.RTC object should not be used to set/get time, however the set_time() and adjtime() methods in this module may be used.
On baremetal ports the Real Time Clock (RTC) must be initialized by the application using either the machine.RTC class or the set_time() method. On those ports adjtime()` and time zones are not available and localtime() as well as gmtime() return the same time as set in the RTC.

Functions¶

utime.localtime([secs])¶

Convert a time expressed in seconds since the Epoch (see above) into a 9-tuple which contains: (year, month, mday, hour, minute, second, weekday, yearday, isdst) If secs is not provided or None, then the current time from the RTC is used.

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
isdst is 0=no daylight savings in effect, 1=dst in effect, -1=unknown

utime.gmtime([secs])¶: Gmtime is identical to localtime except that it returns UTC time.

utime.mktime()¶: This is inverse function of localtime. Its argument is a full 9-tuple which expresses a time as per localtime. The values for weekday and yearday are ignored. It returns an integer which is the number of seconds since the Epoch.

utime.tzset(zone)¶

Set the conversion rules between UTC time and local time used by mktime() and localtime(). The argument is a string that specifies the name of the zones with/without daylight savings, the standard offset to UTC, and the start/end times of daylight savings. The full rules are described in CPython’s time module, except that there is no zoneinfo database.

As an example, the America/Los_Angeles time zone can be specified as PST+8PDT,M3.2.0/2,M11.1.0/2 where: * PST is the standard time zone name * +8 is the offset to convert from PST to UTC * PDT is the daylight savings time zone name * M3.2.0/2 designates that daylight savings starts at 2am (“/2”) on sunday (“.0”)

of the second week (“.2”) of the third month (“M3.”)

M11.1.0/2 designates that daylight savings ends at 2am on sunday of the first week of the eleventh month

See https://sites.google.com/a/usapiens.com/opnode/time-zones for a lit of zone specs.

utime.set_time(secs)¶

Sets the current time to the specified number of seconds since the Epoch.

set_time() is an extension to CPython’s time module.

utime.adjtime(microseconds)¶

Gradually adjusts the current time by the number of microseconds specified and returns the adjustment that still remains if one is in progress. The semantics are the same as for the POSIX adjtime call.

There is an implementation-dependent maximum adjustment, but in general, if the step is large set_time should be used.

adjtime() is an extension to CPython’s time module.

utime.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.

utime.sleep_ms(ms)¶: Delay for given number of milliseconds, should be positive or 0.

utime.sleep_us(us)¶: Delay for given number of microseconds, should be positive or 0.

utime.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.

utime.ticks_us()¶: Just like ticks_ms() above, but in microseconds.

utime.ticks_cpu()¶

Similar to ticks_ms() and ticks_us(), but with the highest possible resolution in the system. This is usually CPU clocks, and that’s why the function is named that way. But it doesn’t have to be a CPU clock, some other timing source available in a system (e.g. high-resolution timer) can be used instead. The exact timing unit (resolution) of this function is not specified on utime module level, but documentation for a specific port may provide more specific information. This function is intended for very fine benchmarking or very tight real-time loops. Avoid using it in portable code.

Availability: Not every port implements this function.

utime.ticks_add(ticks, delta)¶

Offset ticks value by a given number, which can be either positive or negative. Given a ticks value, this function allows to calculate 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))

utime.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) arithmetics to produce correct result even for wrap-around values (as long as they not too distant inbetween, see below). The function returns 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.

Informal rationale of the constraints above: Suppose you are locked in a room with no means to monitor passing of time except a standard 12-notch clock. Then if you look at dial-plate now, and don’t look again for another 13 hours (e.g., if you fall for a long sleep), then once you finally look again, it may seem to you that only 1 hour has passed. To avoid this mistake, just look at the clock regularly. Your application should do the same. “Too long sleep” metaphor also maps directly to application behavior: don’t let your application run any single task for too long. Run tasks in steps, and do time-keeping inbetween.

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 .

utime.time()¶: Returns the number of seconds, as an integer, since the Epoch, assuming that underlying RTC is set and maintained as described above. If an RTC is not set, this function returns number of seconds since a port-specific reference point in time (for embedded boards without a battery-backed RTC, usually since power up or reset). If you want to develop portable MicroPython application, you should not rely on this function to provide higher than second precision. If you need higher precision, use ticks_ms() and ticks_us() functions, if you need calendar time, localtime() without an argument is a better choice.

Difference to CPython

In CPython, this function returns number of seconds since Unix epoch, 1970-01-01 00:00 UTC, as a floating-point, usually having microsecond precision. With MicroPython, some ports use the same Epoch, and if floating-point precision allows, return sub-second precision. Embedded hardware usually doesn’t have floating-point precision to represent both long time ranges and subsecond precision, so they use an integer value with second precision. Some embedded hardware also lacks battery-powered RTC, and returns the number of seconds since the last power-up or from another relative, hardware-specific, point (e.g. reset).

utime – time related functions¶

Functions¶

`utime` – time related functions¶