Source code for cocotb.clock

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"""A clock class."""

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

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


class BaseClock:
    """Base class to derive from."""

    def __init__(self, signal):
        self.signal = signal

    @lazy_property
    def log(self):
        return SimLog("cocotb.{}.{}".format(type(self).__qualname__, self.signal._name))


[docs]class Clock(BaseClock): 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". .. deprecated:: 1.5 Using ``None`` as the *units* argument is deprecated, use ``'step'`` instead. """ def __init__( self, signal, period: Union[float, Real, Decimal], units: str = "step" ): BaseClock.__init__(self, signal) if units is None: warnings.warn( 'Using units=None is deprecated, use units="step" instead.', DeprecationWarning, stacklevel=2, ) units = "step" # don't propagate deprecated value 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
[docs] 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