testbed/cocotb__cocotb/src/cocotb/clock.py

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"""A clock class."""

import itertools
from decimal import Decimal
from numbers import Real
from typing import Union

from cocotb._py_compat import cached_property
from cocotb.log import SimLog
from cocotb.triggers import Timer
from cocotb.utils import get_sim_steps, get_time_from_sim_steps


class Clock:
    r"""Simple 50:50 duty cycle clock driver.

    Instances of this class should call its :meth:`start` method
    and pass the coroutine object to one of the functions in :ref:`task-management`.

    This will create a clocking task that drives the signal at the
    desired period/frequency.

    Example:

    .. code-block:: python

        c = Clock(dut.clk, 10, 'ns')
        await cocotb.start(c.start())

    Args:
        signal: The clock pin/signal to be driven.
        period (int): The clock period. Must convert to an even number of
            timesteps.
        units (str, optional): One of
            ``'step'``, ``'fs'``, ``'ps'``, ``'ns'``, ``'us'``, ``'ms'``, ``'sec'``.
            When *units* is ``'step'``,
            the timestep is determined by the simulator (see :make:var:`COCOTB_HDL_TIMEPRECISION`).

    If you need more features like a phase shift and an asymmetric duty cycle,
    it is simple to create your own clock generator (that you then :func:`~cocotb.start`):

    .. code-block:: python

        async def custom_clock():
            # pre-construct triggers for performance
            high_time = Timer(high_delay, units="ns")
            low_time = Timer(low_delay, units="ns")
            await Timer(initial_delay, units="ns")
            while True:
                dut.clk.value = 1
                await high_time
                dut.clk.value = 0
                await low_time

    If you also want to change the timing during simulation,
    use this slightly more inefficient example instead where
    the :class:`Timer`\ s inside the while loop are created with
    current delay values:

    .. code-block:: python

        async def custom_clock():
            while True:
                dut.clk.value = 1
                await Timer(high_delay, units="ns")
                dut.clk.value = 0
                await Timer(low_delay, units="ns")

        high_delay = low_delay = 100
        await cocotb.start(custom_clock())
        await Timer(1000, units="ns")
        high_delay = low_delay = 10  # change the clock speed
        await Timer(1000, units="ns")

    .. versionchanged:: 1.5
        Support ``'step'`` as the *units* argument to mean "simulator time step".

    .. versionchanged:: 2.0
        Passing ``None`` as the *units* argument was removed, use ``'step'`` instead.
    """

    def __init__(
        self, signal, period: Union[float, Real, Decimal], units: str = "step"
    ):
        self.signal = signal
        self.period = get_sim_steps(period, units)
        self.half_period = get_sim_steps(period / 2, units)
        self.frequency = 1 / get_time_from_sim_steps(self.period, units="us")
        self.hdl = None
        self.signal = signal
        self.coro = None
        self.mcoro = None

    async def start(self, cycles=None, start_high=True):
        r"""Clocking coroutine.  Start driving your clock by :func:`cocotb.start`\ ing a
        call to this.

        Args:
            cycles (int, optional): Cycle the clock *cycles* number of times,
                or if ``None`` then cycle the clock forever.
                Note: ``0`` is not the same as ``None``, as ``0`` will cycle no times.
            start_high (bool, optional): Whether to start the clock with a ``1``
                for the first half of the period.
                Default is ``True``.

                .. versionadded:: 1.3
        """
        t = Timer(self.half_period)
        if cycles is None:
            it = itertools.count()
        else:
            it = range(cycles)

        # branch outside for loop for performance (decision has to be taken only once)
        if start_high:
            for _ in it:
                self.signal.value = 1
                await t
                self.signal.value = 0
                await t
        else:
            for _ in it:
                self.signal.value = 0
                await t
                self.signal.value = 1
                await t

    def __str__(self):
        return type(self).__qualname__ + "(%3.1f MHz)" % self.frequency

    @cached_property
    def log(self):
        return SimLog(f"cocotb.{type(self).__qualname__}.{self.signal._name}")