Tape and disk loaders for the Commodore 64
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Tape and disk loaders for the Commodore 64

An advanced analysis to support the preservation effort for the most popular 8-bit computer ever

About the Book

This book is an effort to collect technical details about tape and disk loaders for the Commodore 64 in a single place, providing the ultimate reference material for a comprehensive software preservation effort.

About the Author

Luigi Di Fraia
Luigi Di Fraia

I am a DevOps Engineer so I get to work with the latest technologies and open-source software such as Terraform, Ansible, Docker, Kubernetes, Helm, within an AWS-based platform. However, in my private time I enjoy retro-computing: my projects are often related to the Commodore 64. The latter was the first programmable home computer I had when I was a teenager. My passion for this system has only grown over time, to the point that I designed both new hardware interfaces and software for it. You can find a few more details around here and within my WordPress.com blog.

From an education/background perspective I should mention that I hold a Master’s Degree in Electronics Engineering and I am specialized in the design of electronic medical equipment. However, my thesis was worked at within the Department of Electronic Measurements of the University of Naples “Federico II”, where I developed part of the analog interface and the whole firmware for accurate distance measurements by means of ultrasonic echo detection. An accurate detection of the on-set point of the ultrasonic echo was achieved by using a Discrete Kalman Filter, implemented on a Microchip DSP.

After obtaining my Masters Degree I completed a five-month Network and Network Security post-graduate course that gave me a better view of the TCP/IP stack, of the PKI infrastructure, and of Security Hardening methods for computer networks. Most of the Networking material I became familiar with during the course formed the basis of Cisco’s “CCNA” curriculum.

Along with these education experiences, I always enjoyed computer programming: very early in BASIC for my Commodore 64, then using AMOS for my Commodore Amiga 500, through to command-line PC applications written in “C”. I subsequently got exposed to the Win32 API for building GUI applications, and eventually to the GTK+ 2 framework, which I adopted heavily due to its multi-platform support.

Having acquired some experience with embedded system development during the work on my thesis, and having enjoyed it, I also started making plans about designing an embedded device of mine, the DC2N. During the discovery activities I abandoned the red path (Microchip) in order to walk along the blue one (Atmel) and I started using the AVR family of 8-bit micro-controllers: from the ATMega32 onwards. A few years ago I started developing for the Atmel SAM7S and NXP LPC17xx family of 32-bit ARM Cortex processors. Very recently I settled for ST’s low-cost STM32 family of microprocessors that provide good value for price.

Table of Contents

  • Foreword
  • Chapter One: Disk drive hardware
    • How the block-sync and byte-sync signals of a Commodore 1541 drive work
    • How to tell if a disk sector was overwritten by a CBM drive
  • Chapter Two: Digital formats for storing low-level tape and disk contents
    • Disk images (NIB, G64, FDI, RAW)
    • Tape images (TAP)
  • Chapter Three: Disk loaders
    • Vorpal (later)
  • Chapter Four: Tape loaders
    • Data transfer
    • Difference between READ and WRITE signals
    • Digital tape sampling, the TAP format
    • Commercial tape loaders
    • Mega-save instance used in Cauldron (non-IRQ-based loader)
    • Ocean loader instance used in Terminator 2 (IRQ-based)
    • Timing example: decoding 4 bits
    • Pulse threshold for tape loaders
    • CIAs and Vectors

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