Library Reference

Test Results

The exceptions in this module can be raised at any point by any code and will terminate the test.

cocotb.result.raise_error(obj, msg)[source]

Create a TestError exception and raise it after printing a traceback.

Deprecated since version 1.3: Use raise TestError(msg) instead of this function. A stacktrace will be printed by cocotb automatically if the exception is unhandled.

Parameters
  • obj – Object with a log method.

  • msg (str) – The log message.

cocotb.result.create_error(obj, msg)[source]

Like raise_error(), but return the exception rather than raise it, simply to avoid too many levels of nested try/except blocks.

Deprecated since version 1.3: Use TestError(msg) directly instead of this function.

Parameters
  • obj – Object with a log method.

  • msg (str) – The log message.

exception cocotb.result.ReturnValue(retval)[source]

Helper exception needed for Python versions prior to 3.3.

exception cocotb.result.TestComplete(*args, **kwargs)[source]

Exception showing that the test was completed. Sub-exceptions detail the exit status.

exception cocotb.result.ExternalException(exception)[source]

Exception thrown by external functions.

exception cocotb.result.TestError(*args, **kwargs)[source]

Exception showing that the test was completed with severity Error.

exception cocotb.result.TestFailure(*args, **kwargs)[source]

Exception showing that the test was completed with severity Failure.

exception cocotb.result.TestSuccess(*args, **kwargs)[source]

Exception showing that the test was completed successfully.

exception cocotb.result.SimFailure(*args, **kwargs)[source]

Exception showing that the simulator exited unsuccessfully.

Writing and Generating tests

class cocotb.test(f, timeout=None, expect_fail=False, expect_error=False, skip=False, stage=None)[source]

Decorator to mark a function as a test.

All tests are coroutines. The test decorator provides some common reporting etc., a test timeout and allows us to mark tests as expected failures.

Used as @cocotb.test(...).

Parameters
  • timeout (int, optional) – value representing simulation timeout (not implemented).

  • expect_fail (bool, optional) – Don’t mark the result as a failure if the test fails.

  • expect_error (bool or exception type or tuple of exception types, optional) –

    If True, consider this test passing if it raises any Exception, and failing if it does not. If given an exception type or tuple of exception types, catching only a listed exception type is considered passing. This is primarily for cocotb internal regression use for when a simulator error is expected.

    Users are encouraged to use the following idiom instead:

    @cocotb.test()
    def my_test(dut):
        try:
            yield thing_that_should_fail()
        except ExceptionIExpect:
            pass
        else:
            assert False, "Exception did not occur"
    

    Changed in version 1.3: Specific exception types can be expected

  • skip (bool, optional) – Don’t execute this test as part of the regression.

  • stage (int, optional) – Order tests logically into stages, where multiple tests can share a stage.

class cocotb.coroutine(func)[source]

Decorator class that allows us to provide common coroutine mechanisms:

log methods will log to cocotb.coroutine.name.

join() method returns an event which will fire when the coroutine exits.

Used as @cocotb.coroutine.

class cocotb.external(func)[source]

Decorator to apply to an external function to enable calling from cocotb. This currently creates a new execution context for each function that is called. Scope for this to be streamlined to a queue in future.

class cocotb.function(func)[source]

Decorator class that allows a function to block.

This allows a function to internally block while externally appear to yield.

class cocotb.hook(f)[source]

Decorator to mark a function as a hook for cocotb.

Used as @cocotb.hook().

All hooks are run at the beginning of a cocotb test suite, prior to any test code being run.

class cocotb.regression.TestFactory(test_function, *args, **kwargs)[source]

Factory to automatically generate tests.

Parameters
  • test_function – The function that executes a test. Must take dut as the first argument.

  • *args – Remaining arguments are passed directly to the test function. Note that these arguments are not varied. An argument that varies with each test must be a keyword argument to the test function.

  • **kwargs – Remaining keyword arguments are passed directly to the test function. Note that these arguments are not varied. An argument that varies with each test must be a keyword argument to the test function.

Assuming we have a common test function that will run a test. This test function will take keyword arguments (for example generators for each of the input interfaces) and generate tests that call the supplied function.

This Factory allows us to generate sets of tests based on the different permutations of the possible arguments to the test function.

For example if we have a module that takes backpressure and idles and have some packet generation routines gen_a and gen_b:

>>> tf = TestFactory(test_function=run_test)
>>> tf.add_option(name='data_in', optionlist=[gen_a, gen_b])
>>> tf.add_option('backpressure', [None, random_backpressure])
>>> tf.add_option('idles', [None, random_idles])
>>> tf.generate_tests()

We would get the following tests:

  • gen_a with no backpressure and no idles

  • gen_a with no backpressure and random_idles

  • gen_a with random_backpressure and no idles

  • gen_a with random_backpressure and random_idles

  • gen_b with no backpressure and no idles

  • gen_b with no backpressure and random_idles

  • gen_b with random_backpressure and no idles

  • gen_b with random_backpressure and random_idles

The tests are appended to the calling module for auto-discovery.

Tests are simply named test_function_N. The docstring for the test (hence the test description) includes the name and description of each generator.

add_option(name, optionlist)[source]

Add a named option to the test.

Parameters
  • name (str) – Name of the option. Passed to test as a keyword argument.

  • optionlist (list) – A list of possible options for this test knob.

generate_tests(prefix='', postfix='')[source]

Generate an exhaustive set of tests using the cartesian product of the possible keyword arguments.

The generated tests are appended to the namespace of the calling module.

Parameters
  • prefix (str) – Text string to append to start of test_function name when naming generated test cases. This allows reuse of a single test_function with multiple TestFactories without name clashes.

  • postfix (str) – Text string to append to end of test_function name when naming generated test cases. This allows reuse of a single test_function with multiple TestFactories without name clashes.

Interacting with the Simulator

class cocotb.binary.BinaryRepresentation[source]
UNSIGNED = 0

Unsigned format

SIGNED_MAGNITUDE = 1

Sign and magnitude format

TWOS_COMPLEMENT = 2

Two’s complement format

class cocotb.binary.BinaryValue(value=None, n_bits=None, bigEndian=True, binaryRepresentation=0, bits=None)[source]

Representation of values in binary format.

The underlying value can be set or accessed using these aliasing attributes:

For example:

>>> vec = BinaryValue()
>>> vec.integer = 42
>>> print(vec.binstr)
101010
>>> print(repr(vec.buff))
'*'
Parameters
  • value (str or int or long, optional) – Value to assign to the bus.

  • n_bits (int, optional) – Number of bits to use for the underlying binary representation.

  • bigEndian (bool, optional) – Interpret the binary as big-endian when converting to/from a string buffer.

  • binaryRepresentation (BinaryRepresentation) – The representation of the binary value (one of UNSIGNED, SIGNED_MAGNITUDE, TWOS_COMPLEMENT). Defaults to unsigned representation.

  • bits (int, optional) – Deprecated: Compatibility wrapper for n_bits.

assign(value)[source]

Decides how best to assign the value to the vector.

We possibly try to be a bit too clever here by first of all trying to assign the raw string as a BinaryValue.binstr, however if the string contains any characters that aren’t 0, 1, X or Z then we interpret the string as a binary buffer.

Parameters

value (str or int or long) – The value to assign.

get_value()[source]

Return the integer representation of the underlying vector.

get_value_signed()[source]

Return the signed integer representation of the underlying vector.

property is_resolvable

Does the value contain any X’s? Inquiring minds want to know.

property value

Integer access to the value. deprecated

property integer

The integer representation of the underlying vector.

property signed_integer

The signed integer representation of the underlying vector.

get_buff()[source]

Attribute buff represents the value as a binary string buffer.

>>> "0100000100101111".buff == "A/"
True
property buff

Access to the value as a buffer.

get_binstr()[source]

Attribute binstr is the binary representation stored as a string of 1 and 0.

property binstr

Access to the binary string.

property n_bits

Access to the number of bits of the binary value.

class cocotb.bus.Bus(entity, name, signals, optional_signals=[], bus_separator='_', array_idx=None)[source]

Wraps up a collection of signals.

Assumes we have a set of signals/nets named entity.<bus_name><separator><signal>.

For example a bus stream_in with signals valid and data is assumed to be named dut.stream_in_valid and dut.stream_in_data (with the default separator ‘_’).

Todo

Support for struct/record ports where signals are member names.

Parameters
  • entity (SimHandle) – SimHandle instance to the entity containing the bus.

  • name (str) – Name of the bus. None for a nameless bus, e.g. bus-signals in an interface or a modport (untested on struct/record, but could work here as well).

  • signals (list or dict) – In the case of an object (passed to drive()/capture()) that has the same attribute names as the signal names of the bus, the signals argument can be a list of those names. When the object has different attribute names, the signals argument should be a dict that maps bus attribute names to object signal names.

  • optional_signals (list or dict, optional) – Signals that don’t have to be present on the interface. See the signals argument above for details.

  • bus_separator (str, optional) – Character(s) to use as separator between bus name and signal name. Defaults to ‘_’.

  • array_idx (int or None, optional) – Optional index when signal is an array.

drive(obj, strict=False)[source]

Drives values onto the bus.

Parameters
  • obj – Object with attribute names that match the bus signals.

  • strict (bool, optional) – Check that all signals are being assigned.

Raises

AttributeError – If not all signals have been assigned when strict=True.

capture()[source]

Capture the values from the bus, returning an object representing the capture.

Returns

A dictionary that supports access by attribute, where each attribute corresponds to each signal’s value.

Return type

dict

Raises

RuntimeError – If signal not present in bus, or attempt to modify a bus capture.

sample(obj, strict=False)[source]

Sample the values from the bus, assigning them to obj.

Parameters
  • obj – Object with attribute names that match the bus signals.

  • strict (bool, optional) – Check that all signals being sampled are present in obj.

Raises

AttributeError – If attribute is missing in obj when strict=True.

class cocotb.clock.Clock(signal, period, units=None)[source]

Simple 50:50 duty cycle clock driver.

Instances of this class should call its start() method and fork() the result. This will create a clocking thread that drives the signal at the desired period/frequency.

Example:

c = Clock(dut.clk, 10, 'ns')
cocotb.fork(c.start())
Parameters
  • 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 None, 'fs', 'ps', 'ns', 'us', 'ms', 'sec'. When no units is given (None) the timestep is determined by the simulator.

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 fork()):

@cocotb.coroutine
def custom_clock():
    # pre-construct triggers for performance
    high_time = Timer(high_delay, units="ns")
    low_time = Timer(low_delay, units="ns")
    yield Timer(initial_delay, units="ns")
    while True:
        dut.clk <= 1
        yield high_time
        dut.clk <= 0
        yield low_time

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

@cocotb.coroutine
def custom_clock():
    while True:
        dut.clk <= 1
        yield Timer(high_delay, units="ns")
        dut.clk <= 0
        yield Timer(low_delay, units="ns")

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

Add a new coroutine.

Just a wrapper around self.schedule which provides some debug and useful error messages in the event of common gotchas.

cocotb.decorators.RunningCoroutine.join(self)

Return a trigger that will fire when the wrapped coroutine exits.

cocotb.decorators.RunningCoroutine.kill(self)

Kill a coroutine.

Triggers

See Simulator Triggers for a list of sub-classes. Below are the internal classes used within cocotb.

class cocotb.triggers.Trigger[source]

Base class to derive from.

abstract prime(callback)[source]

Set a callback to be invoked when the trigger fires.

The callback will be invoked with a single argument, self.

Sub-classes must override this, but should end by calling the base class method.

Do not call this directly within coroutines, it is intended to be used only by the scheduler.

unprime()[source]

Remove the callback, and perform cleanup if necessary.

After being un-primed, a Trigger may be re-primed again in the future. Calling unprime multiple times is allowed, subsequent calls should be a no-op.

Sub-classes may override this, but should end by calling the base class method.

Do not call this directly within coroutines, it is intended to be used only by the scheduler.

class cocotb.triggers.GPITrigger[source]

Base Trigger class for GPI triggers.

Consumes simulation time.

unprime()[source]

Disable a primed trigger, can be re-primed.

Testbench Structure

Driver

class cocotb.drivers.Driver[source]

Class defining the standard interface for a driver within a testbench.

The driver is responsible for serializing transactions onto the physical pins of the interface. This may consume simulation time.

Constructor for a driver instance.

kill()[source]

Kill the coroutine sending stuff.

append(transaction, callback=None, event=None, **kwargs)[source]

Queue up a transaction to be sent over the bus.

Mechanisms are provided to permit the caller to know when the transaction is processed.

Parameters
  • transaction (any) – The transaction to be sent.

  • callback (callable, optional) – Optional function to be called when the transaction has been sent.

  • event (optional) – Event to be set when the transaction has been sent.

  • **kwargs – Any additional arguments used in child class’ _driver_send method.

clear()[source]

Clear any queued transactions without sending them onto the bus.

send[source]

Blocking send call (hence must be “yielded” rather than called).

Sends the transaction over the bus.

Parameters
  • transaction (any) – The transaction to be sent.

  • sync (bool, optional) – Synchronize the transfer by waiting for a rising edge.

  • **kwargs (dict) – Additional arguments used in child class’ _driver_send method.

_driver_send(transaction, sync=True, **kwargs)[source]

Actual implementation of the send.

Sub-classes should override this method to implement the actual send() routine.

Parameters
  • transaction (any) – The transaction to be sent.

  • sync (bool, optional) – Synchronize the transfer by waiting for a rising edge.

  • **kwargs – Additional arguments if required for protocol implemented in a sub-class.

_send[source]

Send coroutine.

Parameters
  • transaction (any) – The transaction to be sent.

  • callback (callable, optional) – Optional function to be called when the transaction has been sent.

  • event (optional) – event to be set when the transaction has been sent.

  • sync (bool, optional) – Synchronize the transfer by waiting for a rising edge.

  • **kwargs – Any additional arguments used in child class’ _driver_send method.

class cocotb.drivers.BitDriver(signal, clk, generator=None)[source]

Bases: object

Drives a signal onto a single bit.

Useful for exercising ready/valid flags.

start(generator=None)[source]

Start generating data.

Parameters

generator (generator, optional) –

Generator yielding data. The generator should yield tuples (on, off) with the number of cycles to be on, followed by the number of cycles to be off. Typically the generator should go on forever.

Example:

bit_driver.start((1, i % 5) for i in itertools.count())

stop()[source]

Stop generating data.

class cocotb.drivers.BusDriver(entity, name, clock, **kwargs)[source]

Bases: cocotb.drivers.Driver

Wrapper around common functionality for buses which have:

  • a list of _signals (class attribute)

  • a list of _optional_signals (class attribute)

  • a clock

  • a name

  • an entity

Parameters
  • entity (SimHandle) – A handle to the simulator entity.

  • name (str or None) – Name of this bus. None for a nameless bus, e.g. bus-signals in an interface or a modport. (untested on struct/record, but could work here as well).

  • clock (SimHandle) – A handle to the clock associated with this bus.

  • **kwargs (dict) – Keyword arguments forwarded to cocotb.Bus, see docs for that class for more information.

Constructor for a driver instance.

_driver_send[source]

Implementation for BusDriver.

Parameters
  • transaction – The transaction to send.

  • sync (bool, optional) – Synchronize the transfer by waiting for a rising edge.

_wait_for_signal[source]

This method will return when the specified signal has hit logic 1. The state will be in the ReadOnly phase so sim will need to move to NextTimeStep before registering more callbacks can occur.

_wait_for_nsignal[source]

This method will return when the specified signal has hit logic 0. The state will be in the ReadOnly phase so sim will need to move to NextTimeStep before registering more callbacks can occur.

class cocotb.drivers.ValidatedBusDriver(entity, name, clock, **kwargs)[source]

Bases: cocotb.drivers.BusDriver

Same as a BusDriver except we support an optional generator to control which cycles are valid.

Parameters
  • entity (SimHandle) – A handle to the simulator entity.

  • name (str) – Name of this bus.

  • clock (SimHandle) – A handle to the clock associated with this bus.

  • valid_generator (generator, optional) – a generator that yields tuples of (valid, invalid) cycles to insert.

Constructor for a driver instance.

_next_valids()[source]

Optionally insert invalid cycles every N cycles.

The generator should yield tuples with the number of cycles to be on followed by the number of cycles to be off. The on cycles should be non-zero, we skip invalid generator entries.

set_valid_generator(valid_generator=None)[source]

Set a new valid generator for this bus.

Monitor

class cocotb.monitors.Monitor(callback=None, event=None)[source]

Base class for Monitor objects.

Monitors are passive ‘listening’ objects that monitor pins going in or out of a DUT. This class should not be used directly, but should be sub-classed and the internal _monitor_recv method should be overridden and decorated as a coroutine. This _monitor_recv method should capture some behavior of the pins, form a transaction, and pass this transaction to the internal _recv method. The _monitor_recv method is added to the cocotb scheduler during the __init__ phase, so it should not be yielded anywhere.

The primary use of a Monitor is as an interface for a Scoreboard.

Parameters
  • callback (callable) – Callback to be called with each recovered transaction as the argument. If the callback isn’t used, received transactions will be placed on a queue and the event used to notify any consumers.

  • event (cocotb.triggers.Event) – Event that will be called when a transaction is received through the internal _recv method. Event.data is set to the received transaction.

wait_for_recv(timeout=None)[source]

With timeout, wait() for transaction to arrive on monitor and return its data.

Parameters

timeout – The timeout value for Timer. Defaults to None.

Returns

Data of received transaction.

_monitor_recv[source]

Actual implementation of the receiver.

Sub-classes should override this method to implement the actual receive routine and call _recv with the recovered transaction.

_recv(transaction)[source]

Common handling of a received transaction.

class cocotb.monitors.BusMonitor(entity, name, clock, reset=None, reset_n=None, callback=None, event=None, bus_separator='_', array_idx=None)[source]

Bases: cocotb.monitors.Monitor

Wrapper providing common functionality for monitoring buses.

property in_reset

Boolean flag showing whether the bus is in reset state or not.

Scoreboard

Common scoreboarding capability.

class cocotb.scoreboard.Scoreboard(dut, reorder_depth=0, fail_immediately=True)[source]

Bases: object

Generic scoreboarding class.

We can add interfaces by providing a monitor and an expected output queue.

The expected output can either be a function which provides a transaction or a simple list containing the expected output.

Todo

Statistics for end-of-test summary etc.

Parameters
  • dut (SimHandle) – Handle to the DUT.

  • reorder_depth (int, optional) – Consider up to reorder_depth elements of the expected result list as passing matches. Default is 0, meaning only the first element in the expected result list is considered for a passing match.

  • fail_immediately (bool, optional) – Raise TestFailure immediately when something is wrong instead of just recording an error. Default is True.

property result

Determine the test result, do we have any pending data remaining?

Returns

If not all expected output was received or error were recorded during the test.

Return type

TestFailure

compare(got, exp, log, strict_type=True)[source]

Common function for comparing two transactions.

Can be re-implemented by a sub-class.

Parameters
  • got – The received transaction.

  • exp – The expected transaction.

  • log – The logger for reporting messages.

  • strict_type (bool, optional) – Require transaction type to match exactly if True, otherwise compare its string representation.

Raises

TestFailure – If received transaction differed from expected transaction when fail_immediately is True. If strict_type is True, also the transaction type must match.

add_interface(monitor, expected_output, compare_fn=None, reorder_depth=0, strict_type=True)[source]

Add an interface to be scoreboarded.

Provides a function which the monitor will callback with received transactions.

Simply check against the expected output.

Parameters
  • monitor – The monitor object.

  • expected_output – Queue of expected outputs.

  • compare_fn (callable, optional) – Function doing the actual comparison.

  • reorder_depth (int, optional) – Consider up to reorder_depth elements of the expected result list as passing matches. Default is 0, meaning only the first element in the expected result list is considered for a passing match.

  • strict_type (bool, optional) – Require transaction type to match exactly if True, otherwise compare its string representation.

Raises

TypeError – If no monitor is on the interface or compare_fn is not a callable function.

Clock

class cocotb.clock.Clock(signal, period, units=None)[source]

Simple 50:50 duty cycle clock driver.

Instances of this class should call its start() method and fork() the result. This will create a clocking thread that drives the signal at the desired period/frequency.

Example:

c = Clock(dut.clk, 10, 'ns')
cocotb.fork(c.start())
Parameters
  • 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 None, 'fs', 'ps', 'ns', 'us', 'ms', 'sec'. When no units is given (None) the timestep is determined by the simulator.

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 fork()):

@cocotb.coroutine
def custom_clock():
    # pre-construct triggers for performance
    high_time = Timer(high_delay, units="ns")
    low_time = Timer(low_delay, units="ns")
    yield Timer(initial_delay, units="ns")
    while True:
        dut.clk <= 1
        yield high_time
        dut.clk <= 0
        yield low_time

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

@cocotb.coroutine
def custom_clock():
    while True:
        dut.clk <= 1
        yield Timer(high_delay, units="ns")
        dut.clk <= 0
        yield Timer(low_delay, units="ns")

high_delay = low_delay = 100
cocotb.fork(custom_clock())
yield Timer(1000, units="ns")
high_delay = low_delay = 10  # change the clock speed
yield Timer(1000, units="ns")
start[source]

Clocking coroutine. Start driving your clock by fork()ing a call to this.

Parameters
  • 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.

Utilities

cocotb.utils.get_sim_time(units=None)[source]

Retrieves the simulation time from the simulator.

Parameters

units (str or None, optional) – String specifying the units of the result (one of None, 'fs', 'ps', 'ns', 'us', 'ms', 'sec'). None will return the raw simulation time.

Returns

The simulation time in the specified units.

cocotb.utils.get_time_from_sim_steps(steps, units)[source]

Calculates simulation time in the specified units from the steps based on the simulator precision.

Parameters
  • steps (int) – Number of simulation steps.

  • units (str) – String specifying the units of the result (one of 'fs', 'ps', 'ns', 'us', 'ms', 'sec').

Returns

The simulation time in the specified units.

cocotb.utils.get_sim_steps(time, units=None)[source]

Calculates the number of simulation time steps for a given amount of time.

Parameters
  • time (numbers.Number) – The value to convert to simulation time steps.

  • units (str or None, optional) – String specifying the units of the result (one of None, 'fs', 'ps', 'ns', 'us', 'ms', 'sec'). None means time is already in simulation time steps.

Returns

The number of simulation time steps.

Return type

int

Raises

ValueError – If given time cannot be represented by simulator precision.

cocotb.utils.pack(ctypes_obj)[source]

Convert a ctypes structure into a Python string.

Parameters

ctypes_obj (ctypes.Structure) – The ctypes structure to convert to a string.

Returns

New Python string containing the bytes from memory holding ctypes_obj.

cocotb.utils.unpack(ctypes_obj, string, bytes=None)[source]

Unpack a Python string into a ctypes structure.

If the length of string is not the correct size for the memory footprint of the ctypes structure then the bytes keyword argument must be used.

Parameters
  • ctypes_obj (ctypes.Structure) – The ctypes structure to pack into.

  • string (str) – String to copy over the ctypes_obj memory space.

  • bytes (int, optional) – Number of bytes to copy. Defaults to None, meaning the length of string is used.

Raises
  • ValueError – If length of string and size of ctypes_obj are not equal.

  • MemoryError – If bytes is longer than size of ctypes_obj.

cocotb.utils.hexdump(x)[source]

Hexdump a buffer.

Parameters

x – Object that supports conversion via the str built-in.

Returns

A string containing the hexdump.

Example

>>> print(hexdump('this somewhat long string'))
0000   74 68 69 73 20 73 6F 6D 65 77 68 61 74 20 6C 6F   this somewhat lo
0010   6E 67 20 73 74 72 69 6E 67                        ng string
cocotb.utils.hexdiffs(x, y)[source]

Return a diff string showing differences between two binary strings.

Parameters
  • x – Object that supports conversion via the str built-in.

  • y – Object that supports conversion via the str built-in.

Example

>>> print(hexdiffs(0, 1))
0000      30                                               0
     0000 31                                               1

>>> print(hexdiffs('a', 'b'))
0000      61                                               a
     0000 62                                               b

>>> print(hexdiffs('this short thing', 'this also short'))
0000      746869732073686F 7274207468696E67 this short thing
     0000 7468697320616C73 6F  2073686F7274 this also  short
class cocotb.utils.ParametrizedSingleton(*args, **kwargs)[source]

A metaclass that allows class construction to reuse an existing instance.

We use this so that RisingEdge(sig) and Join(coroutine) always return the same instance, rather than creating new copies.

cocotb.utils.reject_remaining_kwargs(name, kwargs)[source]

Helper function to emulate Python 3 keyword-only arguments.

Use as:

def func(x1, **kwargs):
    a = kwargs.pop('a', 1)
    b = kwargs.pop('b', 2)
    reject_remaining_kwargs('func', kwargs)
    ...

To emulate the Python 3 syntax:

def func(x1, *, a=1, b=2):
    ...
class cocotb.utils.lazy_property(fget)[source]

A property that is executed the first time, then cached forever.

It does this by replacing itself on the instance, which works because unlike @property it does not define __set__.

This should be used for expensive members of objects that are not always used.

cocotb.utils.want_color_output()[source]

Return True if colored output is possible/requested and not running in GUI.

cocotb.utils.remove_traceback_frames(tb_or_exc, frame_names)[source]

Strip leading frames from a traceback

Parameters
  • tb_or_exc (Union[traceback, BaseException, exc_info]) – Object to strip frames from. If an exception is passed, creates a copy of the exception with a new shorter traceback. If a tuple from sys.exc_info is passed, returns the same tuple with the traceback shortened

  • frame_names (List[str]) – Names of the frames to strip, which must be present.

Simulation Object Handles

Inheritance diagram of cocotb.handle

class cocotb.handle.SimHandleBase(handle, path)[source]

Bases: object

Base class for all simulation objects.

We maintain a handle which we can use for GPI calls.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

class cocotb.handle.RegionObject(handle, path)[source]

Bases: cocotb.handle.SimHandleBase

A region object, such as a scope or namespace.

Region objects don’t have values, they are effectively scopes or namespaces.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

class cocotb.handle.HierarchyObject(handle, path)[source]

Bases: cocotb.handle.RegionObject

Hierarchy objects are namespace/scope objects.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

class cocotb.handle.HierarchyArrayObject(handle, path)[source]

Bases: cocotb.handle.RegionObject

Hierarchy Arrays are containers of Hierarchy Objects.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

class cocotb.handle.NonHierarchyObject(handle, path)[source]

Bases: cocotb.handle.SimHandleBase

Common base class for all non-hierarchy objects.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

property value

A reference to the value

class cocotb.handle.ConstantObject(handle, path, handle_type)[source]

Bases: cocotb.handle.NonHierarchyObject

An object which has a value that can be read, but not set.

We can also cache the value since it is fixed at elaboration time and won’t change within a simulation.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

  • handle_type – The type of the handle (simulator.INTEGER, simulator.ENUM, simulator.REAL, simulator.STRING).

class cocotb.handle.NonHierarchyIndexableObject(handle, path)[source]

Bases: cocotb.handle.NonHierarchyObject

A non-hierarchy indexable object.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

class cocotb.handle.NonConstantObject(handle, path)[source]

Bases: cocotb.handle.NonHierarchyIndexableObject

A non-constant object

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

drivers()[source]

An iterator for gathering all drivers for a signal.

loads()[source]

An iterator for gathering all loads on a signal.

class cocotb.handle.ModifiableObject(handle, path)[source]

Bases: cocotb.handle.NonConstantObject

Base class for simulator objects whose values can be modified.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

setimmediatevalue(value)[source]

Set the value of the underlying simulation object to value.

This operation will fail unless the handle refers to a modifiable object, e.g. net, signal or variable.

We determine the library call to make based on the type of the value because assigning integers less than 32 bits is faster.

Parameters

value (ctypes.Structure, cocotb.binary.BinaryValue, int, double) – The value to drive onto the simulator object.

Raises

TypeError – If target is not wide enough or has an unsupported type for value assignment.

class cocotb.handle.RealObject(handle, path)[source]

Bases: cocotb.handle.ModifiableObject

Specific object handle for Real signals and variables.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

setimmediatevalue(value)[source]

Set the value of the underlying simulation object to value.

This operation will fail unless the handle refers to a modifiable object, e.g. net, signal or variable.

Parameters

value (float) – The value to drive onto the simulator object.

Raises

TypeError – If target has an unsupported type for real value assignment.

class cocotb.handle.EnumObject(handle, path)[source]

Bases: cocotb.handle.ModifiableObject

Specific object handle for enumeration signals and variables.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

setimmediatevalue(value)[source]

Set the value of the underlying simulation object to value.

This operation will fail unless the handle refers to a modifiable object, e.g. net, signal or variable.

Parameters

value (int) – The value to drive onto the simulator object.

Raises

TypeError – If target has an unsupported type for integer value assignment.

class cocotb.handle.IntegerObject(handle, path)[source]

Bases: cocotb.handle.ModifiableObject

Specific object handle for Integer and Enum signals and variables.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

setimmediatevalue(value)[source]

Set the value of the underlying simulation object to value.

This operation will fail unless the handle refers to a modifiable object, e.g. net, signal or variable.

Parameters

value (int) – The value to drive onto the simulator object.

Raises

TypeError – If target has an unsupported type for integer value assignment.

class cocotb.handle.StringObject(handle, path)[source]

Bases: cocotb.handle.ModifiableObject

Specific object handle for String variables.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

setimmediatevalue(value)[source]

Set the value of the underlying simulation object to value.

This operation will fail unless the handle refers to a modifiable object, e.g. net, signal or variable.

Parameters

value (str) – The value to drive onto the simulator object.

Raises

TypeError – If target has an unsupported type for string value assignment.

cocotb.handle.SimHandle(handle, path=None)[source]

Factory function to create the correct type of SimHandle object.

Parameters
  • handle (int) – The GPI handle to the simulator object.

  • path (str) – Path to this handle, None if root.

Returns

The SimHandle object.

Raises

TestError – If no matching object for GPI type could be found.

Implemented Testbench Structures

Drivers

AMBA

Advanced Microcontroller Bus Architecture.

class cocotb.drivers.amba.AXI4LiteMaster(entity, name, clock, **kwargs)[source]

AXI4-Lite Master.

TODO: Kill all pending transactions if reset is asserted.

Constructor for a driver instance.

write(address, value, byte_enable=0xf, address_latency=0, data_latency=0)[source]

Write a value to an address.

Parameters
  • address (int) – The address to write to.

  • value (int) – The data value to write.

  • byte_enable (int, optional) – Which bytes in value to actually write. Default is to write all bytes.

  • address_latency (int, optional) – Delay before setting the address (in clock cycles). Default is no delay.

  • data_latency (int, optional) – Delay before setting the data value (in clock cycles). Default is no delay.

  • sync (bool, optional) – Wait for rising edge on clock initially. Defaults to True.

Returns

The write response value.

Return type

BinaryValue

Raises

AXIProtocolError – If write response from AXI is not OKAY.

read(address, sync=True)[source]

Read from an address.

Parameters
  • address (int) – The address to read from.

  • sync (bool, optional) – Wait for rising edge on clock initially. Defaults to True.

Returns

The read data value.

Return type

BinaryValue

Raises

AXIProtocolError – If read response from AXI is not OKAY.

class cocotb.drivers.amba.AXI4Slave(entity, name, clock, memory, callback=None, event=None, big_endian=False, **kwargs)[source]

AXI4 Slave

Monitors an internal memory and handles read and write requests.

Constructor for a driver instance.

Avalon

class cocotb.drivers.avalon.AvalonMM(entity, name, clock, **kwargs)[source]

Bases: cocotb.drivers.BusDriver

Avalon Memory Mapped Interface (Avalon-MM) Driver.

Currently we only support the mode required to communicate with SF avalon_mapper which is a limited subset of all the signals.

Blocking operation is all that is supported at the moment, and for the near future as well. Posted responses from a slave are not supported.

Constructor for a driver instance.

class cocotb.drivers.avalon.AvalonMaster(entity, name, clock, **kwargs)[source]

Avalon Memory Mapped Interface (Avalon-MM) Master.

Constructor for a driver instance.

write(address, value)[source]

Issue a write to the given address with the specified value.

Parameters
  • address (int) – The address to write to.

  • value (int) – The data value to write.

Raises

TestError – If master is read-only.

read(address, sync=True)[source]

Issue a request to the bus and block until this comes back.

Simulation time still progresses but syntactically it blocks.

Parameters
  • address (int) – The address to read from.

  • sync (bool, optional) – Wait for rising edge on clock initially. Defaults to True.

Returns

The read data value.

Return type

BinaryValue

Raises

TestError – If master is write-only.

class cocotb.drivers.avalon.AvalonMemory(entity, name, clock, readlatency_min=1, readlatency_max=1, memory=None, avl_properties={}, **kwargs)[source]

Bases: cocotb.drivers.BusDriver

Emulate a memory, with back-door access.

Constructor for a driver instance.

class cocotb.drivers.avalon.AvalonST(entity, name, clock, **kwargs)[source]

Bases: cocotb.drivers.ValidatedBusDriver

Avalon Streaming Interface (Avalon-ST) Driver

Constructor for a driver instance.

class cocotb.drivers.avalon.AvalonSTPkts(entity, name, clock, **kwargs)[source]

Bases: cocotb.drivers.ValidatedBusDriver

Avalon Streaming Interface (Avalon-ST) Driver, packetized.

Constructor for a driver instance.

OPB

class cocotb.drivers.opb.OPBMaster(entity, name, clock, **kwargs)[source]

On-chip peripheral bus master.

Constructor for a driver instance.

write(address, value, sync=True)[source]

Issue a write to the given address with the specified value.

Parameters
  • address (int) – The address to read from.

  • value (int) – The data value to write.

  • sync (bool, optional) – Wait for rising edge on clock initially. Defaults to True.

Raises

OPBException – If write took longer than 16 cycles.

read(address, sync=True)[source]

Issue a request to the bus and block until this comes back.

Simulation time still progresses but syntactically it blocks.

Parameters
  • address (int) – The address to read from.

  • sync (bool, optional) – Wait for rising edge on clock initially. Defaults to True.

Returns

The read data value.

Return type

BinaryValue

Raises

OPBException – If read took longer than 16 cycles.

XGMII

class cocotb.drivers.xgmii.XGMII(signal, clock, interleaved=True)[source]

Bases: cocotb.drivers.Driver

XGMII (10 Gigabit Media Independent Interface) driver.

Parameters
  • signal (SimHandle) – The XGMII data bus.

  • clock (SimHandle) – The associated clock (assumed to be driven by another coroutine).

  • interleaved (bool, optional) – Whether control bits are interleaved with the data bytes or not.

If interleaved the bus is

byte0, byte0_control, byte1, byte1_control, …

Otherwise expect

byte0, byte1, …, byte0_control, byte1_control, …

static layer1(packet)[source]

Take an Ethernet packet (as a string) and format as a layer 1 packet.

Pad to 64 bytes, prepend preamble and append 4-byte CRC on the end.

Parameters

packet (str) – The Ethernet packet to format.

Returns

The formatted layer 1 packet.

Return type

str

idle()[source]

Helper function to set bus to IDLE state.

terminate(index)[source]

Helper function to terminate from a provided lane index.

Parameters

index (int) – The index to terminate.

Monitors

Avalon

class cocotb.monitors.avalon.AvalonST(entity, name, clock, **kwargs)[source]

Bases: cocotb.monitors.BusMonitor

Avalon-ST bus.

Non-packetized so each valid word is a separate transaction.

class cocotb.monitors.avalon.AvalonSTPkts(entity, name, clock, **kwargs)[source]

Bases: cocotb.monitors.BusMonitor

Packetized Avalon-ST bus.

Parameters
  • name, clock (entity,) – see BusMonitor

  • config (dict) – bus configuration options

  • report_channel (bool) – report channel with data, default is False Setting to True on bus without channel signal will give an error

XGMII

class cocotb.monitors.xgmii.XGMII(signal, clock, interleaved=True, callback=None, event=None)[source]

Bases: cocotb.monitors.Monitor

XGMII (10 Gigabit Media Independent Interface) Monitor.

Assumes a single vector, either 4 or 8 bytes plus control bit for each byte.

If interleaved is True then the control bits are adjacent to the bytes.

Parameters
  • signal (SimHandle) – The XGMII data bus.

  • clock (SimHandle) – The associated clock (assumed to be driven by another coroutine).

  • interleaved (bool, optional) – Whether control bits are interleaved with the data bytes or not.

If interleaved the bus is

byte0, byte0_control, byte1, byte1_control, …

Otherwise expect

byte0, byte1, …, byte0_control, byte1_control, …

Miscellaneous

Signal Tracer for WaveDrom

class cocotb.wavedrom.Wavedrom(obj)[source]

Base class for a WaveDrom compatible tracer.

sample()[source]

Record a sample of the signal value at this point in time.

clear()[source]

Delete all sampled data.

get(add_clock=True)[source]

Return the samples as a list suitable for use with WaveDrom.

class cocotb.wavedrom.trace(*args, **kwargs)[source]

Context manager to enable tracing of signals.

Arguments are an arbitrary number of signals or buses to trace. We also require a clock to sample on, passed in as a keyword argument.

Usage:

with trace(sig1, sig2, a_bus, clk=clk) as waves:
    # Stuff happens, we trace it

    # Dump to JSON format compatible with WaveDrom
    j = waves.dumpj()

Developer-focused

The Scheduler

Note

The scheduler object should generally not be interacted with directly - the only part of it that a user will need is encapsulated in fork(), everything else works behind the scenes.

cocotb.scheduler = <cocotb.scheduler.Scheduler object>

The global scheduler instance.

class cocotb.scheduler.Scheduler[source]

The main scheduler.

Here we accept callbacks from the simulator and schedule the appropriate coroutines.

A callback fires, causing the react method to be called, with the trigger that caused the callback as the first argument.

We look up a list of coroutines to schedule (indexed by the trigger) and schedule them in turn. NB implementors should not depend on the scheduling order!

Some additional management is required since coroutines can return a list of triggers, to be scheduled when any one of the triggers fires. To ensure we don’t receive spurious callbacks, we have to un-prime all the other triggers when any one fires.

Due to the simulator nuances and fun with delta delays we have the following modes:

Normal mode
  • Callbacks cause coroutines to be scheduled

  • Any pending writes are cached and do not happen immediately

ReadOnly mode
  • Corresponds to cbReadOnlySynch (VPI) or vhpiCbLastKnownDeltaCycle (VHPI). In this state we are not allowed to perform writes.

Write mode
  • Corresponds to cbReadWriteSynch (VPI) or vhpiCbEndOfProcesses (VHPI) In this mode we play back all the cached write updates.

We can legally transition from normal->write by registering a ReadWrite callback, however usually once a simulator has entered the ReadOnly phase of a given timestep then we must move to a new timestep before performing any writes. The mechanism for moving to a new timestep may not be consistent across simulators and therefore we provide an abstraction to assist with compatibility.

Unless a coroutine has explicitly requested to be scheduled in ReadOnly mode (for example wanting to sample the finally settled value after all delta delays) then it can reasonably be expected to be scheduled during “normal mode” i.e. where writes are permitted.

react(trigger)[source]

Called when a trigger fires.

We ensure that we only start the event loop once, rather than letting it recurse.

unschedule(coro)[source]

Unschedule a coroutine. Unprime any pending triggers

queue(coroutine)[source]

Queue a coroutine for execution

queue_function(coro)[source]

Queue a coroutine for execution and move the containing thread so that it does not block execution of the main thread any longer.

run_in_executor(func, *args, **kwargs)[source]

Run the coroutine in a separate execution thread and return a yieldable object for the caller.

add(coroutine)[source]

Add a new coroutine.

Just a wrapper around self.schedule which provides some debug and useful error messages in the event of common gotchas.

add_test(test_coro)[source]

Called by the regression manager to queue the next test

schedule(coroutine, trigger=None)[source]

Schedule a coroutine by calling the send method.

Parameters
  • coroutine (cocotb.decorators.coroutine) – The coroutine to schedule.

  • trigger (cocotb.triggers.Trigger) – The trigger that caused this coroutine to be scheduled.

finish_scheduler(exc)[source]

Directly call into the regression manager and end test once we return the sim will close us so no cleanup is needed.

cleanup()[source]

Clear up all our state.

Unprime all pending triggers and kill off any coroutines stop all externals.