utime – time related functions

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

Time Epoch: Unix port uses standard for POSIX systems epoch of 1970-01-01 00:00:00 UTC. However, embedded ports use epoch of 2000-01-01 00:00:00 UTC.

Maintaining actual calendar date/time: This requires a Real Time Clock (RTC). On systems with underlying OS (including some RTOS), an RTC may be implicit. Setting and maintaining actual calendar time is responsibility of OS/RTOS and is done outside of MicroPython, it just uses OS API to query date/time. On baremetal ports however system time depends on machine.RTC() object. The current calendar time may be set using machine.RTC().datetime(tuple) function, and maintained by following means:

  • By a backup battery (which may be an additional, optional component for a particular board).
  • Using networked time protocol (requires setup by a port/user).
  • Set manually by a user on each power-up (many boards then maintain RTC time across hard resets, though some may require setting it again in such case).

If actual calendar time is not maintained with a system/MicroPython RTC, functions below which require reference to current absolute time may behave not as expected.

Functions

utime.localtime([secs])

Convert a time 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.

  • 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
utime.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.

utime.sleep(seconds)

Sleep for the given number of seconds. Seconds can be a floating-point number to sleep for a fractional number of seconds. Note that other MicroPython ports may not accept 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 arbitrary reference point, that wraps after some (unspecified) value. The value should be treated as opaque, suitable for use only with ticks_diff().

utime.ticks_us()

Just like ticks_ms above, but in microseconds.

utime.ticks_cpu()

Similar to ticks_ms and ticks_us, but with higher resolution (usually CPU clocks).

utime.ticks_diff(old, new)

Measure period between consecutive calls to ticks_ms(), ticks_us(), or ticks_cpu(). The value returned by these functions may wrap around at any time, so directly subtracting them is not supported. ticks_diff() should be used instead. “old” value should actually precede “new” value in time, or result is undefined. This function should not be used to measure arbitrarily long periods of time (because ticks_*() functions wrap around and usually would have short period). The expected usage pattern is implementing event polling with timeout:

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

Returns the number of seconds, as an integer, since the Epoch, assuming that underlying RTC is set and maintained as decsribed 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, only Unix port uses the same Epoch, and if floating-point precision allows, returns sub-second precision. Embedded hardware usually doesn’t have floating-point precision to represent both long time ranges and subsecond precision, so they use integer value with second precision. Some embedded hardware also lacks battery-powered RTC, so returns number of seconds since last power-up or from other relative, hardware-specific point (e.g. reset).