Polymorphic Blocks

Polymorphic Blocks is an open-source, Python-based hardware description language (HDL) for printed circuit boards (PCBs). Unlike some existing PCB HDLs, our goal is not just "schematics in text" (or "Verilog for PCBs" 😨), but to increase design automation and accessibility by improving on the fundamental design model. Expressing designs and libraries in code not only allows basic automation like step-and-repeat with for loops, but also allows subcircuits to be reactive to their usage like automatically sizing power converters by output voltage and current draw. Adding programming language concepts, like type systems, interfaces, and inheritance, can also raise the level of design, while polymorphism allows libraries to be generic while retaining fine-grained control for system designers.

Check out the the getting started tutorial document for a more usage-focused introduction. For a slightly deeper technical overview, including summaries of example projects, check out our UIST'20 paper and recorded talks.

This is alpha software, and is a continuing work-in-progress. Backwards compatibility is (currently) not guaranteed. See Project Status for more details.

Example

From the getting started tutorial, this code defines a board with a USB Type-C connector powering (through a buck converter for 3.3V step-down) a microcontroller which drives a LED and reads a switch.

self.usb = self.Block(UsbDeviceCReceptacle())

with self.implicit_connect(
    ImplicitConnect(self.usb.pwr, [Power]),
    ImplicitConnect(self.usb.gnd, [Common]),
) as imp:
  self.usb_reg = imp.Block(BuckConverter(output_voltage=3.3*Volt(tol=0.05)))

with self.implicit_connect(
    ImplicitConnect(self.usb_reg.pwr_out, [Power]),
    ImplicitConnect(self.usb.gnd, [Common]),
) as imp:
  self.mcu = imp.Block(Lpc1549_48())
  (self.swd, ), _ = self.chain(imp.Block(SwdCortexTargetHeader()), self.mcu.swd)
     
  (self.led, ), _ = self.chain(self.mcu.new_io(DigitalBidir), imp.Block(IndicatorLed()))
  (self.sw, ), _ = self.chain(imp.Block(DigitalSwitch()), self.mcu.new_io(DigitalBidir))

To get to a PCB, the user would then:

• Drop the HDL into a top-level block and add top-level compilation code.
• Select block refinements as needed, eg choosing a TPS561201 regulator for the abstract BuckConverter.
• Generate the netlist.
• Import into KiCad for board layout.
• As circuit changes are needed, re-generate the netlist and update the board layout.

Selected Features

Circuit Design Features

• An electronics model that performs circuit checks above ERC, like checking voltage compatibility and current limits.
• Automatic parts selection for discrete components, using E-series for resistors and parts tables for capacitors, inductors, and discrete semiconductors.
  • ... including E-series resistive dividers.
• Common subcircuit blocks that implement well-known design practices:
  • ... including buck and boost converters that automatically run component sizing calculations.
  • ... including some analog circuits like resistive dividers, low-pass RCs, and certain opamp topologies.
• Common subcircuit blocks that implement the datasheet application circuits:
  • ... including microcontrollers, like the LPC1549 and STM32F103, and supporting manual (but checked) pin assignment.
  • ... including a USB Type C receptacle (USB 2.0 type), so you can't forget the CC pull-down resistors.

Layout Integration Features

• Stable netlists, allowing in-progress board layouts to be updated from modified HDL.
  • Note: this depends on stable names in the HDL. We've got some thoughts for a more powerful version of this, though.
• Support for hierarchy tools in Kicad Action Plugins, including layout save/restore and replicate.

Getting Started

See the getting started tutorial, once you have a working installation. The reference document listing ports, links, and parts may also be useful.

Setup

Python and Packages

You will need a Python 3.7+ installation with the protobuf package.

The packages can be installed using pip:

pip install protobuf

On Ubuntu, you may need to select a particular version of Python for pip, using python3.8 -m pip instead of pip directly.

DigiKey Data

Many of the parts libraries use data downloaded from DigiKey (a parts distributor), but our interpretation of their Terms of Use is that we cannot redistribute those files. You will need to download your own parts tables, follow these instructions.

Know of open-source parts tables that we could use instead? Or do you represent DigiKey and think we've read the Terms of Use too strictly? Please let us know!

Unit Tests

You can run the unit test suite to verify that everything works - all tests should be green. The test suite includes both unit level tests and example boards.

python -m unittest discover

Additional Resources

Project Status

This is alpha software, and is a continuing work-in-progress. There are significant model and API changes in progress, and backwards compatibility is (currently) not guaranteed until those stabilize.

If you're looking for a mature PCB design tool that just works, this currently isn't it (yet). For a mature and open-source graphical schematic capture and board layout tool, check out KiCad. However, if you are interested in trying something new, we're happy to help you and answer questions.

If you're interested in collaborating or contributing, please reach out to us, and we do take pull requests. Ultimately, we'd like to see an open-source PCB HDL that increases design automation, reduces tedious work, and makes electronics more accessible to everyone.

Current development focuses on supporting intermediate-level PCB projects, ie those an advanced hobbyist would make. Typical systems would involve power conditioning circuits, a microcontroller, and supporting peripherals (possibly including analog blocks). Note that there is no hard-coded architecture, eg, a microcontroller is not needed, and you can make pure analog boards. We believe that the system should be able to handle projects that are much more or much less complex, as long as supporting libraries exist.

We have no plans to address board layout; KiCad's board layout tool is very functional for manual layout. However, there are cross-cutting concerns (eg, layout-aware pin assignment, HDL-to-layout diff and update, multipack devices) that we may address.

Examples

Example boards, including layouts, are available in the examples/ directory, structured as unit tests and including board layouts:

• test_blinky.py: all variations of blinky from the getting started tutorial.
• test_simon.py: a Simon memory game implementation with a speaker and 12v illuminated dome buttons.
• test_can_adapter.py: an isolated CANbus to USB (type-C, USB-FS) adapter.
• test_debugger.py: an SWD (Serial Wire Debug) programmer / debugger that is partially firmware-compatible with ST-Link/V2 clones.
• test_high_switch.py: a +12V high-side lights driver, for controlling automotive lights from CAN.
• test_datalogger.py: a CANbus to SD card data recorder, with a supercapacitor to cleanly close the SD card file on power loss.
• Other examples in this directory may not be complete. We may remove older examples as we refactor code. Library changes may result in netlist differences if the layouts are updated.

Developing

See developing.md for developer documentation.

Misc

• What is EDG?: Embedded Device Generation (or more generally Electronic Device Generation) was a prior version of this project that focused on algorithms and models for embedded device synthesis, though it lacked a user-facing component. This project is a continuation of that work focusing on an end-to-end system, and for most of its development cycle has been called edg. But, for the purposes of writing research papers, naming collisions are confusing and bad, and we chose to keep the repo and paper name consistent.
• Why is there so much CANbus stuff?: Many of the example designs were built for a solar car project.
• Why is there so much USB Type-C stuff?: USB Type-C is the one connector to rule them all.