An Introduction to FPGA Programming with Python Using MyHDL

As the world of Field-Programmable Gate Arrays (FPGAs) continues to evolve, more developers are looking for ways to leverage the power of FPGAs for specialized tasks such as high-speed data processing and real-time computing. Traditionally, FPGA programming has been dominated by Hardware Description Languages (HDLs) like Verilog and VHDL. However, recent tools and libraries have emerged that allow developers to use more familiar high-level languages like Python to design FPGA systems. One such tool is MyHDL, a Python library that enables FPGA programming by converting Python code into HDL.

In this article, we'll introduce FPGA programming using MyHDL, explaining its advantages and providing a beginner-friendly guide to get started with Python for FPGA design.

Why Use MyHDL?

FPGA programming with Verilog or VHDL can be daunting, especially for software developers who are more accustomed to writing code in higher-level languages. MyHDL bridges the gap between hardware and software by allowing developers to use Python, one of the most widely used programming languages, for FPGA design. Here’s why MyHDL stands out:

Familiar Syntax: MyHDL allows you to write hardware designs in Python, making it easier for software developers to transition to hardware programming.
Simulation and Testing: MyHDL supports simulation directly in Python, allowing you to quickly test and validate your hardware designs.
HDL Conversion: Once you've written and tested your design in Python, MyHDL can convert it to Verilog or VHDL, making it compatible with FPGA synthesis tools.
Code Reusability: Python’s flexibility and MyHDL’s design enable you to create reusable modules that can be integrated into various FPGA projects.

Getting Started with MyHDL

To begin using MyHDL, you’ll need to install the library, set up your Python environment, and get familiar with some basic hardware concepts. Let’s break down the process.

1. Setting Up the Environment

Start by installing MyHDL through Python’s package manager, pip:

bash

pip install myhdl

Once installed, you’re ready to start writing Python code that can be converted into an FPGA-ready format.

2. Writing Your First MyHDL Code

Here’s a simple example of creating a basic AND gate in MyHDL, which is one of the simplest logic components used in digital circuits.

python

from myhdl import block, always_comb, Signal

@block
def and_gate(a, b, c):
@always_comb
def logic():
c.next = a & b
return logic

Test the design

a, b, c = [Signal(bool(0)) for i in range(3)]
inst = and_gate(a, b, c)
inst.run_sim()

In this code:

The and_gate function is a Python block that describes the behavior of an AND gate.
The @block decorator tells MyHDL that this function is a hardware block.
The always_comb decorator indicates that the function inside defines a combinational logic process.
Signal objects are used to represent the inputs and outputs of the gate.

3. Simulating the Design

One of MyHDL’s key strengths is its ability to run simulations in Python, which helps to validate the logic before synthesizing it to hardware. You can write a test bench to simulate the AND gate behavior like this:

python

from myhdl import delay, instance

@block
def testbench():
a, b, c = [Signal(bool(0)) for _ in range(3)]
gate = and_gate(a, b, c)

@instance
def stimulus():
    print("Testing AND gate:")
    for i in range(4):
        a.next, b.next = i // 2, i % 2
        yield delay(10)
        print(f"a = {int(a)}, b = {int(b)} => c = {int(c)}")

return gate, stimulus

tb = testbench()
tb.run_sim()

This testbench simulates all input combinations of the AND gate and prints the result for each one. The use of yield delay(10) is a simple way to step through time during the simulation, helping you verify that the gate behaves as expected.

4. Converting to Verilog or VHDL

Once your Python design is ready, you can convert it into Verilog or VHDL for synthesis on an actual FPGA. Here’s how you convert the AND gate example into Verilog:

python

from myhdl import toVerilog

a, b, c = [Signal(bool(0)) for i in range(3)]
and_gate_inst = and_gate(a, b, c)
toVerilog(and_gate, a, b, c)

This generates a Verilog file that can be integrated into a standard FPGA toolchain, such as Xilinx ISE or Intel Quartus, for synthesis and deployment onto an FPGA board.
MyHDL vs Traditional HDLs
Feature MyHDL Verilog / VHDL
Language Python-based, high-level Low-level, specialized for hardware
Ease of Learning Easier for software developers Steeper learning curve
Simulation Simulated directly in Python Separate tools for simulation
HDL Conversion Converts to Verilog/VHDL Native Verilog/VHDL
Code Reusability Highly reusable thanks to Python Reusable but requires more boilerplate
Tool Support Limited FPGA tool support Broad support for FPGA development tools

Advantages of Using MyHDL

Faster Prototyping: MyHDL allows developers to leverage Python’s rapid prototyping capabilities for FPGA development. Designs can be tested in Python and then converted to hardware description languages.

Python Ecosystem: Python’s large library ecosystem enables you to integrate FPGA design with other tasks, such as machine learning, data processing, and more.

Modularity: MyHDL’s Python-based approach encourages modular and reusable design, helping developers create scalable FPGA solutions.

Conclusion

FPGA programming doesn’t have to be restricted to traditional HDLs like Verilog or VHDL. With MyHDL, Python developers can enter the world of hardware design, using a familiar language to describe, simulate, and test their circuits. Whether you're developing complex digital systems or experimenting with FPGA designs for the first time, MyHDL provides an accessible and powerful solution.

By bridging the gap between software and hardware, MyHDL opens up new possibilities for developers to create high-performance systems with ease.