Homebrew CPUs: Messing around with a J1

Victor Yurkovsky May 29, 2015

In this article I will examine James Bowman's excellent J1 CPU; I will then proceed to mess around with various parts of it, making it smaller, more appropriate to my particular application, and possibly faster.  I hope this will show you how easy it is to fiddle around with homemade CPUs and encourage you to make something weird and wonderful.

J1 CPU

My hat is off to James Bowman.  J1 is pretty cool.  It is a stack machine; it executes instructions in one cycle, it is...


BGA and QFP at Home 1 - A Practical Guide.

Victor Yurkovsky October 13, 20132 comments

It is almost universally accepted by the hobbyists that you can't work with high-density packages at home.  That is entirely incorrect.  I've been assembling and reflowing BGA circuit boards at home for a few years now.  BGAs and 0.5mm-pitch QFPs are well within the realm of a determined amateur. 

This series of articles presents practical information on designing and assembling boards with high-density packages at home.  While the focus is on FPGA packages, most of...


Windows XP and Win32 - the Platform of the Future!

Victor Yurkovsky October 7, 20132 comments

Over the past decade I often wondered why anyone uses Windows.  It's just so... proprietary.  And pedestrian.  As I grew up my OS of choice went nothing to CPM to DOS (on Apple ][), GEM on Atari ST,  MS-DOS, DOS extenders, Mac OS, Windows NT, Windows XP, Linux...  Now, I again find myself a fan of Windows XP, the platform of the future.  (I am still a fan of bare metal, of course).Maybe I am not totally serious, but I, a self-proclaimed freedom lover and...


PC and SP for a small CPU

Victor Yurkovsky July 23, 2013

Ok, let's make a small stack-based CPU.

I will start where the rubber meets the road - the PC/stack subsystem that I like referring to as the 'legs'. As usual, I will present a design with a twist.

Not having a large design team, deadlines and million-dollar fab runs when designing CPUs creates a truly different environment. I can actually sit at the kitchen table and doodle around with CPU designs to my heart's content. I can try really ridiculous approaches, and work without a...


PicoBlaze - Program RAM Access for an Interactive Monitor

Victor Yurkovsky June 14, 20132 comments

I have a confession to make: I love PicoBlaze!  There are many reasons to love it.  It is a tiny CPU (96 Spartan3 slices or 26 Spartan6 slices plus a BRAM).  It is simple.  It is bug-free.  It's pretty fast.  It can reduce the size and the complexity of your design - instead of debugging a big state machine, just throw one (or more) of these in.  Add a serial output and you can debug your fpga from inside out!However, there are a few problems.  The...


StrangeCPU #4. Microcode

Victor Yurkovsky May 13, 20137 comments
Summary:

Sliding windows containing runs of microcode.

Table of Contents:

StrangeCPU #3. Instruction Slides - The Strangest CPU Yet!

Victor Yurkovsky March 18, 201311 comments
Summary:

Decoding instructions with a Sliding Window system.  0-Bit Sliding Register Windows.

Table of Contents:

StrangeCPU #2. Sliding Window Token Machines

Victor Yurkovsky March 5, 201313 comments
Summary:

An in-depth exploration of Sliding Window Token Machines; ARM notes.

Table of Contents:

StrangeCPU #1. A new CPU

Victor Yurkovsky February 25, 20136 comments

Summary: In this multi-part series I will share with you a design, implementation notes and code for a slightly different kind of a CPU featuring a novel token machine that resolves an 8-bit token to pretty much any address in a 32-bit or even 64-bit address space, using not much more than an adder.

Table of Contents:
  • Part 1: A new CPU - technology review, re-examination of the premises;  StrangeCPU concepts; x86 notes.

VGA Output in 7 Slices. Really.

Victor Yurkovsky September 25, 20121 comment

Ridiculous? Read on - I will show you how to generate VGA timing in seven XilinxR Spartan3R slices.Some time ago I needed to output video to a VGA monitor for my Apple ][ FPGA clone.  Obviously (I thought), VGA's been done before and all I had to do was find some Verilog code and drop it into my design.  As is often the case (with me anyway), the task proved to be very different from my imagined 'couple of hours to integrate the IP'.I found some example code for my board.  I...


StrangeCPU #1. A new CPU

Victor Yurkovsky February 25, 20136 comments

Summary: In this multi-part series I will share with you a design, implementation notes and code for a slightly different kind of a CPU featuring a novel token machine that resolves an 8-bit token to pretty much any address in a 32-bit or even 64-bit address space, using not much more than an adder.

Table of Contents:
  • Part 1: A new CPU - technology review, re-examination of the premises;  StrangeCPU concepts; x86 notes.

BGA and QFP at Home 1 - A Practical Guide.

Victor Yurkovsky October 13, 20132 comments

It is almost universally accepted by the hobbyists that you can't work with high-density packages at home.  That is entirely incorrect.  I've been assembling and reflowing BGA circuit boards at home for a few years now.  BGAs and 0.5mm-pitch QFPs are well within the realm of a determined amateur. 

This series of articles presents practical information on designing and assembling boards with high-density packages at home.  While the focus is on FPGA packages, most of...


StrangeCPU #2. Sliding Window Token Machines

Victor Yurkovsky March 5, 201313 comments
Summary:

An in-depth exploration of Sliding Window Token Machines; ARM notes.

Table of Contents:

StrangeCPU #3. Instruction Slides - The Strangest CPU Yet!

Victor Yurkovsky March 18, 201311 comments
Summary:

Decoding instructions with a Sliding Window system.  0-Bit Sliding Register Windows.

Table of Contents:

PC and SP for a small CPU

Victor Yurkovsky July 23, 2013

Ok, let's make a small stack-based CPU.

I will start where the rubber meets the road - the PC/stack subsystem that I like referring to as the 'legs'. As usual, I will present a design with a twist.

Not having a large design team, deadlines and million-dollar fab runs when designing CPUs creates a truly different environment. I can actually sit at the kitchen table and doodle around with CPU designs to my heart's content. I can try really ridiculous approaches, and work without a...


VGA Output in 7 Slices. Really.

Victor Yurkovsky September 25, 20121 comment

Ridiculous? Read on - I will show you how to generate VGA timing in seven XilinxR Spartan3R slices.Some time ago I needed to output video to a VGA monitor for my Apple ][ FPGA clone.  Obviously (I thought), VGA's been done before and all I had to do was find some Verilog code and drop it into my design.  As is often the case (with me anyway), the task proved to be very different from my imagined 'couple of hours to integrate the IP'.I found some example code for my board.  I...


StrangeCPU #4. Microcode

Victor Yurkovsky May 13, 20137 comments
Summary:

Sliding windows containing runs of microcode.

Table of Contents:

Homebrew CPUs: Messing around with a J1

Victor Yurkovsky May 29, 2015

In this article I will examine James Bowman's excellent J1 CPU; I will then proceed to mess around with various parts of it, making it smaller, more appropriate to my particular application, and possibly faster.  I hope this will show you how easy it is to fiddle around with homemade CPUs and encourage you to make something weird and wonderful.

J1 CPU

My hat is off to James Bowman.  J1 is pretty cool.  It is a stack machine; it executes instructions in one cycle, it is...


FPGA Assemblers and Time Machines

Victor Yurkovsky September 3, 20121 comment

Flashback to 1986. A young man has a crazy idea - he wants to make a CPU all by himself. He is reading early Xilinx manuals cover to cover as if they were novels. Yes, you are quick - this is indeed a (mostly) true story about me and my dream, suddenly made possible by this new FPGA technology.

Sadly more than 20 years went by before my first CPU ran in a Xilinx FPGA. Why did it take so long? Every few years I set up the tools and every time I walked away, scared silly. As the years...


Windows XP and Win32 - the Platform of the Future!

Victor Yurkovsky October 7, 20132 comments

Over the past decade I often wondered why anyone uses Windows.  It's just so... proprietary.  And pedestrian.  As I grew up my OS of choice went nothing to CPM to DOS (on Apple ][), GEM on Atari ST,  MS-DOS, DOS extenders, Mac OS, Windows NT, Windows XP, Linux...  Now, I again find myself a fan of Windows XP, the platform of the future.  (I am still a fan of bare metal, of course).Maybe I am not totally serious, but I, a self-proclaimed freedom lover and...