More Examples¶
Apart from the examples covered with full tutorials in the previous sections,
the directory cocotb/examples/
contains some more smaller modules you may want to take a look at.
Adder¶
The directory cocotb/examples/adder/
contains an adder
RTL in both Verilog and VHDL,
an adder_model
implemented in Python,
and the cocotb testbench with two defined tests a simple adder_basic_test()
and
a slightly more advanced adder_randomised_test()
.
This example does not use any Driver
, Monitor
, or Scoreboard
; not even a clock.
D Flip-Flop¶
The directory cocotb/examples/dff/
contains a simple D flip-flop, implemented in both VDHL and Verilog.
The HDL has the data input port d
, the clock port c
, and the data output q
with an initial state of 0
.
No reset port exists.
The cocotb testbench checks the initial state first, then applies random data to the data input.
The flip-flop output is captured at each rising edge of the clock and compared to the applied input data using a Scoreboard
.
The testbench defines a BitMonitor
(a sub-class of Monitor
) as a pendant to the cocotb-provided BitDriver
.
The BitDriver
’s start()
and stop()
methods are used
to start and stop generation of input data.
A TestFactory
is used to generate the random tests.
Matrix Multiplier¶
The directory cocotb/examples/matrix_multiplier
contains a module for multiplying two matrices together,
implemented in both VHDL and SystemVerilog.
The module takes two matrices a_i
and b_i
as inputs
and provides the resulting matrix c_o
as an output.
On each rising clock edge,
c_o
is calculated and output.
When input valid_i
is high
and c_o
is calculated,
valid_o
goes high to signal a valid output value.
The testbench defines MatrixInMonitor
and MatrixOutMonitor
(both sub-classes of BusMonitor
)
and a test case test_multiply
.
MatrixInMonitor
watches for valid input matrices,
then does the multiplication in Python
and stores the result as the expected output matrix.
MatrixOutMonitor
watches for valid output matrices
and compares the result to the expected value.
The testbench makes use of TestFactory
and random data generators
to test many sets of matrices,
and Scoreboard
to compare expected and actual results.
The number of data bits for each entry in the matrices, as well as the row and column counts for each matrix, are configurable in the Makefile.
Note
The example module uses one-dimensional arrays in the port definition to represent the matrices.
Mean¶
The directory cocotb/examples/mean/
contains a module that calculates the mean value of a
data input bus i
(with signals i_data
and i_valid
) and
outputs it on o
(with i_data
and o_valid
).
It has implementations in both VHDL and SystemVerilog.
The testbench defines a StreamBusMonitor
(a sub-class of BusMonitor
), a clock generator,
a value_test
helper coroutine and a few tests.
Test mean_randomised_test
uses the StreamBusMonitor
to
feed a Scoreboard
with the collected transactions on input bus i
.
Mixed Language¶
The directory cocotb/examples/mixed_language/
contains two toplevel HDL files,
one in VHDL, one in SystemVerilog, that each instantiate the endian_swapper
in
SystemVerilog and VHDL in parallel and chains them together so that the endianness is swapped twice.
Thus, we end up with SystemVerilog+VHDL instantiated in VHDL and SystemVerilog+VHDL instantiated in SystemVerilog.
The cocotb testbench pulls the reset on both instances and checks that they behave the same.
AXI Lite Slave¶
The directory cocotb/examples/axi_lite_slave/
contains …
Mixed-signal (analog/digital)¶
This example with two different designs shows how cocotb can be used in an analog-mixed signal (AMS) simulation, provided your simulator supports this. Such an AMS setup involves a digital and an analog simulation kernel, and also provides means to transfer data between the digital and the analog domain.
The “-AMS” variants of the common digital HDLs (VHDL-AMS, Verilog-AMS and SystemVerilog-AMS) and languages like Spice can be used to express the analog behavior of your circuit.
Due to limitations of the underlying simulator interfaces (VPI, VHPI, FLI), cocotb cannot directly access the analog domain but has to resort to e.g. HDL helper code. Thus, unlike the other examples, part of this testbench is implemented with cocotb and the helper part with HDL.