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Setting Up a Dev Environment in Visual Studio Code #

Python Debugging #

1. Create a Python Virtual Environment #

python3 -m venv /path/to/new/virtual/environment

2. Start Virtual Environment #

shell command
bash/zsh source /bin/activate
fish source /bin/activate.fish
csh/tcsh source /bin/activate.csh

3. Install Requirements #

put the following in a file called requirements.txt


then call pip install -r requirements.txt

4. Setup Python Debugging in Visual Studio Code #

setup a launch.json file as follows:

    "version": "0.2.0",
    "configurations": [
            "name": "Python: attach cocotb",
            "type": "python",
            "request": "attach",
            "host": "localhost",
            "port": 5679,

5. Set a Breakpoint #

put the following code where you want to set a breakpoint. For example, if I wanted to step through cocotb startup I’d put this code into __init__.py in my cocotb directory inside my virtual environment located at lib/python<version number>/site-packages/cocotb/__init__.py

    import debugpy
    listen_host, listen_port = debugpy.listen(("localhost", 5679))
    # Suspend execution until debugger attaches
    # Break into debugger for user control
    breakpoint()  # or debugpy.breakpoint() on 3.6 and below

5. Run make #

run make in your cocotb testbench, it will halt and wait for you to connect the debugger.

6. Start Debug Session #

hit the debug button and in the left hand side pane, run “python: attach cocotb” to attach debugger.


Compiled Library Debugging (C/C++) #

Sorry to all readers, but I’m using a mac so this will be how to attach lldb to cocotb. lldb is mac’s built in debugger and is very similar to gdb.

  1. Run your cocotb testbench with make COCOTB_ATTACH=200. This pauses cocotb in the _embed_init_python function in gpi_embed.cpp file for 200 seconds, you can set it to however many seconds you need.


rm -f results.xml
/Library/Developer/CommandLineTools/usr/bin/make -f Makefile results.xml
rm -f results.xml
MODULE=testbench TESTCASE= TOPLEVEL=count_up TOPLEVEL_LANG=verilog \
         /opt/homebrew/bin/vvp -M .venv/lib/python3.10/site-packages/cocotb/libs -m libcocotbvpi_icarus   sim_build/sim.vvp 
     -.--ns INFO     gpi                                ..mbed/gpi_embed.cpp:110  in set_program_name_in_venv        Using Python virtual environment interpreter at /.venv/bin/python
     -.--ns ERROR    gpi                                ..mbed/gpi_embed.cpp:158  in _embed_init_python              Waiting for 200 seconds - attach to PID 26301 with your debugger

NOTE the PID # returned from running make with COCOTB_ATTACH. You can now connect to this process with lldb

  1. lldb in a new terminal

  2. run process attach --pid <PIDNUMBER> i.e. process attach --pid 12345

  3. refer to lldb man pages for how to step, set breakpoints, etc.

useful commands:

  • image lookup -vn gpi_get_handle_by_nam
  • memory read -s1 -fu -c10000 0x<address> --force
  • breakpoint set --name <name of function>
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