PYRTL#
A collection of classes providing simple RTL specification, simulation, tracing, and testing suitable for teaching and research. Simplicity, usability, clarity, and extensibility rather than performance or optimization is the overarching goal. With PyRTL you can use the full power of Python to describe complex synthesizable digital designs, simulate and test them, and export them to Verilog.
Quick links#
Get an overview from the PyRTL Project Webpage
Read through Example PyRTL Code
File a Bug or Issue Report
Contribute to project on GitHub
Installation#
Automatic installation:
pip install pyrtl
PyRTL is listed in PyPI and can be
installed with pip or pip3. If the above command fails
due to insufficient permissions, you may need to do sudo pip install pyrtl
(to install as superuser) or pip install --user pyrtl
(to install as a
normal user).
PyRTL is tested to work with Python 3.8+.
Design, Simulate, and Inspect in 15 lines#
1import pyrtl
2
3a = pyrtl.Input(8,'a') # input "pins"
4b = pyrtl.Input(8,'b')
5q = pyrtl.Output(8,'q') # output "pins"
6gt5 = pyrtl.Output(1,'gt5')
7
8result = a + b # makes an 8-bit adder
9q <<= result # assigns output of adder to out pin
10gt5 <<= result > 5 # does a comparison, assigns that to different pin
11
12# simulate and output the resulting waveform to the terminal
13sim = pyrtl.Simulation()
14sim.step_multiple({'a':[0,1,2,3,4], 'b':[2,2,3,3,4]})
15sim.tracer.render_trace()
After you have PyRTL installed, you should be able to cut and paste the above into a file and run it with Python. The result you should see, drawn right into the terminal, is the output of the simulation. While a great deal of work has gone into making hardware design in PyRTL as friendly as possible, please don’t mistake that for a lack of depth. You can just as easily export to Verilog or other hardware formats, view results with your favorite waveform viewer, build hardware transformation passes, run JIT-accelerated simulations, design, test, and even verify hugely complex digital systems, and much more. Most critically of all it is easy to extend with your own approaches to digital hardware development as you find necessary.
Overview of PyRTL#
If you are brand new to PyRTL we recommend that you start with the PyRTL Code Examples which will show you most of the core functionality in the context of a complete design.
PyRTL Classes:#
Perhaps the most important class to understand is WireVector
, which
is the basic type from which you build all hardware. If you are coming to
PyRTL from Verilog, a WireVector
is closest to a multi-bit wire.
Every new WireVector
builds a set of wires which you can then connect
with other WireVector
through overloaded operations such as
addition or bitwise or. A bunch of other related classes, including
Input
, Output
, Const
, and Register
are
all derived from WireVector
. Coupled with MemBlock
(and
RomBlock
), this is all a user needs to create a functional hardware
design.
After specifying a hardware design, there are then options to simulate your design right in PyRTL, synthesize it down to primitive 1-bit operations, optimize it, and export it to Verilog (along with a testbench).
Simulation#
PyRTL provides tools for simulation and viewing simulation traces. Simulation
is how your hardware is “executed” for the purposes of testing, and three
different classes help you do that: Simulation
,
FastSimulation
and CompiledSimulation
. All three have
almost the same interface and, except for a few debugging cases, can be used
interchangeably. Typically one starts with Simulation
and then moves
up to FastSimulation
when performance begins to matter.
Both Simulation
and FastSimulation
take an instance of
SimulationTrace
as an argument (or makes an empty
SimulationTrace
by default), which stores a list of the signals as
they are simulated. This trace can then be rendered to the terminal with
WaveRenderer
, although unless there are some problems with the
default configurations, most end users should not need to even be aware of
WaveRenderer
. The examples describe other ways that the trace may be
handled, including extraction as a test bench and export to a VCD file.
Optimization#
WireVector
and MemBlock
are just “sugar” over a core set of
primitives, and the final design is built up incrementally as a graph of these
primitives. WireVectors
connects these “primitives”,
which connect to other WireVectors
. Each primitive is a
LogicNet
, and a Block
is a graph of
LogicNets
. Typically a full design is stored in a single
Block
. The function working_block()
returns the block on
which we are implicitly working. Hardware transforms may make a new
Block
from an old one. For example, see PostSynthBlock
.
Errors#
Finally, when things go wrong you may hit on one of two Exceptions
, neither
of which is likely recoverable automatically (which is why we limited them to
only two). The intention is that PyrtlError
is intended to capture end
user errors such as invalid constant strings and mis-matched bitwidths. In
contrast, PyrtlInternalError
captures internal invariants and assertions
over the core logic graph which should never be hit when constructing designs
in the normal ways. If you hit a confusing PyrtlError
or any
PyrtlInternalError
feel free to file an issue.