Tag Archives: HDL

FPGA

Unconventional uses of FPGAs

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My favorite phenomenon in digital circuitry is when digital threatens to become analog again. For example, a lot of people are interested in the idea of overclocking an FPGA for more performance and are usually encouraged not to do so. However, thinking about the reasons why overclocking goes wrong and learning to understand the issues with overclocking can allow you to achieve a stable overclock or at least help you understand your chip better. This is only one example of exploring odd behavior of FPGAs when pushing beyond suggested limits.

Every sensor is a temperature sensor, nearly everything is a resistor or a conductor if you try hard enough and anything is an antenna. Datasheets are just a suggestion, and finally, often we pretend things are ideal, when they often are not.

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FPGA

FPGA – Development Board Selection

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The focus of this article is on the process of selecting an FPGA development board. A focus is placed on beginners because more advanced users have probably developed an intuition for this process for themselves already. I will not be making a lot of specific suggestion in this guide, but I will link some pages with some more specific suggestions. This guide will help you actually select a board out of those suggestions.

The process is actually quite complicated and nuanced, it depends on quite a few situational details that are worth thinking about. Some initial thoughts are…

  1. Current skill level in general electrical engineering and software development
  2. What they want to make with the FPGA
  3. Whether this is someone looking at FPGAs as a hobby or as a future career
    1. Hobbyists might be interested in open source tooling
    2. Those looking towards a career in the field probably want to look at AMD/Xilinx FPGAs/SoCs to start, unless they are looking at low power solutions, in which case Lattice is a good place to start
  4. How much money they have to spend and the likelihood this is a 4-6 month interest or a career long investment
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FPGA

Growing as an FPGA Developer

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March 19, 2023 – Initial

I get asked pretty often about how to get into FPGA design or how to become a good or even great FPGA developer. Since I get asked quite often, I decided to put my thoughts down here instead of typing it out again and again forever. I hope what I write here will help you on your journey. I think some of the content might be useful to non-FPGA developers even though I don’t really plan for it to be as such.

This article is meant for readers who have already made it through their first FPGA course, maybe they are in a masters program or they might be in the first few years of their new job as an FPGA developer. It is not really meant for beginners but might be useful for them none the less.

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FPGA

FPGA – Xilinx JTAG to AXI Master from XSDB and Python

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One of the most annoying things when working on an early design on an FPGA development kit is a lack of run-time register interfaces without a lot of effort.

While looking for an interface that would work on basically any Vivado supported Xilinx FPGA I came across the JTAG to AXI Master core supplied by Xilinx. Unfortunately it has a cumbersome interface that is intended for the user to drive from Vivado’s TCL console which is not always the most convenient. Others have been looking for a C API to interact with the hw_server directly. There seems to be someone that has had put together a C library but I was unable to get the files. I wanted something easier to use anyways so I began to look elsewhere for a solution.

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FPGA

FPGA – LittleRiscy RISC-V RV32I Emulator and HDL Core

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LittleRiscy is an RV32I RISC-V emulator and HDL core that I have decided to release as an open source project. The project is a work in progress.

LittleRiscy’s GIT repository contains an instruction set emulator written in C++ and a CPU core written in SystemVerilog. The emulator has been validated against some simple test binaries and the SystemVerilog code has been converted to C++ using Verilator to validate that it behaves functionally identical when running the same test binaries.

At this time, LittleRiscy has been deployed on a Xilinx Series 7 FPGA using Xilinx Vivado and has blinked some LEDs with a simple binary.

The goal of LittleRiscy is to create a simple CPU core for a unique purpose. It will be a classic RISC pipeline with no debugger, no interrupts, no ability to load new code at runtime, and limited peripherals. Inspired by CHIPS2.0 and the PIOs in the RP2040, it will be used to process AXI-Streams for packet processing or digital signal processing when data rates are low enough that custom RTL logic is not required and a CPU is both smaller and simpler. To further simplify creation of software for the core, the AXI-Stream input interface could stall the CPU on read if empty and the output interface could stall the CPU on write if full, negating the requirement for the software to check flags during execution. For some demanding tasks, it should be easy to add a handful of custom instructions to improve throughput.