Release Notes

All releases are available from the GitHub Releases Page.

cocotb 1.3.0

Released on 08 January 2020

This will likely be the last release to support Python 2.7.

New features

Notable changes and bug fixes

  • DeprecationWarnings are now shown in the output by default.

  • Tracebacks are now preserved correctly for exceptions in Python 2. The tracebacks in all Python versions are now a little shorter.

  • cocotb.external() and cocotb.function() now work more reliably and with fewer race conditions.

  • A failing assert will be considered a test failure. Previously, it was considered a test error.

  • drivers() and loads() now also work correctly in Python 3.7 onwards.

  • cocotb.triggers.Timer can now be used with decimal.Decimal instances, allowing constructs like Timer(Decimal('1e-9'), units='sec') as an alternate spelling for Timer(100, units='us'). (#1114)

  • Many (editorial) documentation improvements.


  • cocotb.result.raise_error and cocotb.result.create_error are deprecated in favor of using Python exceptions directly. TestError can still be used if the same exception type is desired. (#1109)

  • The AvalonSTPktsWithChannel type is deprecated. Use the report_channel argument to AvalonSTPkts instead.

  • The colour attribute of log objects like cocotb.log or some_coro.log is deprecated. Use cocotb.utils.want_color_output() instead. (#1231)

Other news

cocotb 1.2.0

Released on 24 July 2019

New features

  • cocotb is now built as Python package and installable through pip. (#517, #799, #800, #803, #805)

  • Support for async functions and generators was added (Python 3 only). Please have a look at Async functions for an example how to use this new feature.

  • VHDL block statements can be traversed. (#850)

  • Support for Python 3.7 was added.

Notable changes and bug fixes

  • The heart of cocotb, its scheduler, is now even more robust. Many small bugs, inconsistencies and unreliable behavior have been ironed out.

  • Exceptions are now correctly propagated between coroutines, giving users the “natural” behavior they’d expect with exceptions. (#633)

  • The setimmediatevalue() function now works for values larger than 32 bit. (#768)

  • The documentation was cleaned up, improved and extended in various places, making it more consistent and complete.

  • Tab completion in newer versions of IPython is fixed. (#825)

  • Python 2.6 is officially not supported any more. cocotb supports Python 2.7 and Python 3.5+.

  • The cocotb GitHub project moved from potentialventures/cocotb to cocotb/cocotb. Redirects for old URLs are in place.


  • The bits argument to BinaryValue, which is now called n_bits.

  • The logger attribute of log objects like cocotb.log or some_coro.log, which is now just an alias for self.

  • The cocotb.utils.get_python_integer_types function, which was intended to be private.

Known issues

  • Depending on your simulation, cocotb 1.2 might be roughly 20 percent slower than cocotb 1.1. Much of the work in this release cycle went into fixing correctness bugs in the scheduler, sometimes at the cost of performance. We are continuing to investigate this in issue #961. Independent of the cocotb version, we recommend using the latest Python 3 version, which is shown to be significantly faster than previous Python 3 versions, and slightly faster than Python 2.7.

Please have a look at the issue tracker for more outstanding issues and contribution opportunities.

cocotb 1.1

Released on 24 January 2019.

This release is the result of four years of work with too many bug fixes, improvements and refactorings to name them all. Please have a look at the release announcement on the mailing list for further information.

cocotb 1.0

Released on 15 February 2015.

New features

  • FLI support for ModelSim

  • Mixed Language, Verilog and VHDL

  • Windows

  • 300% performance improvement with VHPI interface

  • WaveDrom support for wave diagrams.

cocotb 0.4

Released on 25 February 2014.

New features

  • Issue #101: Implement Lock primitive to support mutex

  • Issue #105: Compatibility with Aldec Riviera-Pro

  • Issue #109: Combine multiple results.xml into a single results file

  • Issue #111: XGMII drivers and monitors added

  • Issue #113: Add operators to BinaryValue class

  • Issue #116: Native VHDL support by implementing VHPI layer

  • Issue #117: Added AXI4-Lite Master BFM

Bugs fixed

  • Issue #100: Functional bug in endian_swapper example RTL

  • Issue #102: Only 1 coroutine wakes up of multiple coroutines wait() on an Event

  • Issue #114: Fix build issues with Cadence IUS simulator

New examples

  • Issue #106: TUN/TAP example using ping

cocotb 0.3

Released on 27 September 2013.

This contains a raft of fixes and feature enhancements.

cocotb 0.2

Released on 19 July 2013.

New features

  • Release 0.2 supports more simulators and increases robustness over 0.1.

  • A centralized installation is now supported (see documentation) with supporting libraries build when the simulation is run for the first time.

cocotb 0.1

Released on 9 July 2013.

  • The first release of cocotb.

  • Allows installation and running against Icarus, VCS, Aldec simulators.