Build options and Environment Variables¶
Makefiles are provided for a variety of simulators in
cocotb/makefiles/simulators. The common Makefile
cocotb/makefiles/Makefile.sim includes the appropriate simulator Makefile based on the contents of the
Makefiles define two targets,
sim, the default target is
Both rules create a results file in the calling directory called
results.xml. This file is a JUnit-compatible output file suitable for use with Jenkins. The
sim targets unconditionally re-runs the simulator whereas the
regression target only re-builds if any dependencies have changed.
Typically the makefiles provided with Cocotb for various simulators use a separate
run target. This allows for a rapid re-running of a simulator if none of the RTL source files have changed and therefore the simulator does not need to recompile the RTL.
- Set this to 1 to enable the GUI mode in the simulator (if supported).
- Selects which simulator Makefile to use. Attempts to include a simulator specific makefile from
- A list of the Verilog source files to include.
- A list of the VHDL source files to include.
- Any arguments or flags to pass to the compile stage of the simulation. Only applies to simulators with a separate compilation stage (currently Icarus and VCS).
- Any arguments or flags to pass to the execution of the compiled simulation. Only applies to simulators with a separate compilation stage (currently Icarus, VCS and GHDL).
- Passed to both the compile and execute phases of simulators with two rules, or passed to the single compile and run command for simulators which don’t have a distinct compilation stage.
- Use to add additional dependencies to the compilation target; useful for defining additional rules to run pre-compilation or if the compilation phase depends on files other than the RTL sources listed in VERILOG_SOURCES or VHDL_SOURCES.
- Use to add additional dependencies to the simulation target.
- Set this to 1 to enable display of VHPI traces when using the nvc VHDL simulator.
- Use to define a scratch directory for use by the simulator. The path is relative to the Makefile location.
If not provided, the default scratch directory is
- Used to indicate the instance in the hierarchy to use as the DUT. If this isn’t defined then the first root instance is used.
Seed the Python random module to recreate a previous test stimulus. At the beginning of every test a message is displayed with the seed used for that execution:
INFO cocotb.gpi __init__.py:89 in _initialise_testbench Seeding Python random module with 1377424946
To recreate the same stimuli use the following:
Use this to override the default behaviour of annotating Cocotb output with ANSI colour codes if the output is a terminal (
COCOTB_ANSI_OUTPUT=1forces output to be ANSI regardless of the type stdout
COCOTB_ANSI_OUTPUT=0supresses the ANSI output in the log messages
- If defined, log lines displayed in terminal will be shorter. It will print only
time, message type (
ERROR) and log message.
- The name of the module(s) to search for test functions. Multiple modules can be specified using a comma-separated list.
The name of the test function(s) to run. If this variable is not defined Cocotb discovers and executes all functions decorated with the
cocotb.testdecorator in the supplied modules.
Multiple functions can be specified in a comma-separated list.
Additional Environment Variables¶
- In order to give yourself time to attach a debugger to the simulator process before it starts to run,
you can set the environment variable
COCOTB_ATTACHto a pause time value in seconds. If set, Cocotb will print the process ID (PID) to attach to and wait the specified time before actually letting the simulator run.
Enable performance analysis of the Python portion of Cocotb. When set, a file
test_profile.pstatwill be written which contains statistics about the cumulative time spent in the functions.
From this, a callgraph diagram can be generated with gprof2dot and
graphviz. See the
profileMake target in the
endian_swapperexample on how to set this up.
- A comma-separated list of modules that should be executed before the first test.
You can also use the
cocotb.hookdecorator to mark a function to be run before test code.
- Default logging level to use. This is set to
Defines how to resolve bits with a value of
Wwhen being converted to integer. Valid settings are:
- raise a
- resolve to
- resolve to
- randomly resolve to a
- Enable additional log output of the coroutine scheduler.
HTTP port to use for debugging Python’s memory usage. When set to e.g.
8088, data will be presented at http://localhost:8088.
This needs the
dowserPython modules installed.
- The root directory of the Cocotb installation.
- The version of the Cocotb installation. You probably don’t want to modify this.