Base Overlay

The purpose of the base overlay design is to allow PYNQ to use peripherals on a board out-of-the-box. The design includes hardware IP to control peripherals on the target board, and connects these IP blocks to the Zynq PS. If a base overlay is available for a board, peripherals can be used from the Python environment immediately after the system boots.

Board peripherals typically include GPIO devices (LEDs, Switches, Buttons), Video, Audio, and other custom interfaces.

As the base overlay includes IP for the peripherals on a board, it can also be used as a reference design for creating new customized overlays.

In the case of general purpose interfaces, for example Pmod or Arduino headers, the base overlay may include a PYNQ MicroBlaze. A PYNQ MicroBlaze allows control of devices with different interfaces and protocols on the same port without requiring a change to the programmable logic design.

See PYNQ Libraries for more information on PYNQ MicroBlazes.

PYNQ-Z1 Block Diagram


The base overlay on PYNQ-Z1 includes the following hardware:

  • HDMI (Input and Output)
  • Microphone in
  • Audio out
  • User LEDs, Switches, Pushbuttons
  • 2x Pmod PYNQ MicroBlaze
  • Arduino PYNQ MicroBlaze
  • 3x Trace Analyzer (PMODA, PMODB, ARDUINO)


The PYNQ-Z1 has HDMI in and HDMI out ports. The HDMI interfaces are connected directly to PL pins. i.e. There is no external HDMI circuitry on the board. The HDMI interfaces are controlled by HDMI IP in the programmable logic.

The HDMI IP is connected to PS DRAM. Video can be streamed from the HDMI in to memory, and from memory to HDMI out. This allows processing of video data from python, or writing an image or Video stream from Python to the HDMI out.

Note that while Jupyter notebook supports embedded video, video captured from the HDMI will be in raw format and would not be suitable for playback in a notebook without appropriate encoding.

For information on the physical HDMI interface ports, see the Digilent HDMI reference for the PYNQ-Z1 board


The HDMI in IP can capture standard HDMI resolutions. After a HDMI source has been connected, and the HDMI controller for the IP is started, it will automatically detect the incoming data. The resolution can be read from the HDMI Python class, and the image data can be streamed to the PS DRAM.


The HDMI out IP supports the following resolutions:

  • 640x480
  • 800x600
  • 1280x720 (720p)
  • 1280x1024
  • 1920x1080 (1080p)*

*While the Pynq-Z1 cannot meet the official HDMI specification for 1080p, some HDMI devices at this resolution may work.

Data can be streamed from the PS DRAM to the HDMI output. The HDMI Out controller contains framebuffers to allow for smooth display of video data.

See example video notebooks in the <Jupyter Dashboard>/base/video directory on the board.

Microphone In

The PYNQ-Z1 board has an integrated microphone on the board and is connected directly to the Zynq PL pins, and does not have an external audio codec. The microphone generates audio data in PDM format.

For more information on the audio hardware, see the Digilent MIC in reference for the PYNQ-Z1 board

See example audio notebooks in the <Jupyter Dashboard>/base/audio directory on the board.

Audio Out

The audio out IP is connected to a standard 3.5mm audio jack on the board. The audio output is PWM driven mono.

For more information on the audio hardware, see the Digilent Audio Out reference for the PYNQ-Z1 board

See example audio notebooks in the <Jupyter Dashboard>/base/audio directory on the board.

User IO

The PYNQ-Z1 board includes two tri-color LEDs, 2 switches, 4 push buttons, and 4 individual LEDs. These IO are connected directly to Zynq PL pins. In the PYNQ-Z1 base overlay, these IO are routed to the PS GPIO, and can be controlled directly from Python.

PYNQ MicroBlaze

PYNQ MicroBlazes are dedicated MicroBlaze soft-processor subsystems that allow peripherals with different IO standards to be connected to the system on demand. This allows a software programmer to use a wide range of peripherals with different interfaces and protocols. By using a PYNQ MicroBlaze, the same overlay can be used to support different peripheral without requiring a different overlay for each peripheral.

The PYNQ-Z1 has two types of PYNQ MicroBlaze: Pmod and Arduio, connecting to each type of corresponding interface. As the board has one Arduino header, and two Pmod ports, there is one instance of the Arduino, and two instances of the PMod PYNQ MicroBlaze in the base overlay.

Each physical interface has a different number of pins and can support different sets of peripherals. Each PYNQ MicroBlaze has the same core architecture, but can have different IP configurations to support the different sets of peripheral and interface pins.

PYNQ MicroBlaze block diagram and examples can be found in MicroBlaze Subsystem.

Trace Analyzer

Trace analyzer blocks are connected to the interface pins for the two Pmod PYNQ MicroBlazes, and the Arduino PYNQ MicroBlaze. The trace analyzer can capture IO signals and stream the data to the PS DRAM for analysis in the Python environment.

Using the Python Wavedrom package, the signals from the trace analyzer can be displayed as waveforms in a Jupyter notebook.

On the base overlay, the trace analyzers are controlled by PS directly. In fact, on other overlays, the trace analyzers can also be controlled by PYNQ MicroBlaze.

See the example notebook in the <Jupyter Dashboard>/base/trace directory on the board.

Python API

The Python API for the peripherals in the base overlay is covered in PYNQ Libraries. Example notebooks are also provided on the board to show how to use the base overlay.

Rebuilding the Overlay

The project files for the overlays can be found here:

<PYNQ repository>/boards/<board>/base


A Makefile is provided to rebuild the base overlay in Linux. The Makefile calls two tcl files. The first Tcl files compiles any HLS IP used in the design. The second Tcl builds the overlay.

To rebuild the overlay, source the Xilinx tools first. Then assuming PYNQ has been cloned:

cd <PYNQ repository>/boards/Pynq-Z1/base


In Windows, the two Tcl files can be sourced in Vivado to rebuild the overlay. The Tcl files to rebuild the overlay can be sourced from the Vivado GUI, or from the Vivado Tcl Shell (command line).

To rebuild from the Vivado GUI, open Vivado. In the Vivado Tcl command line window change to the correct directory, and source the Tcl files as indicated below.

Assuming PYNQ has been cloned:

cd <PYNQ repository>/boards/Pynq-Z1/base
source ./build_base_ip.tcl
source ./base.tcl

To build from the command line, open the Vivado 2017.4 Tcl Shell, and run the following:

cd <PYNQ repository>/boards/Pynq-Z1/base
vivado -mode batch -source build_base_ip.tcl
vivado -mode batch -source base.tcl

Note that you must change to the overlay directory, as the tcl files has relative paths that will break if sourced from a different location.