Software-Defined ROM's Latest Version: The Newest Manifestation of the Programmable Read-Only Memory

In a groundbreaking development, Piers Finlayson, the mastermind behind the project "One ROM to rule them all," has unveiled a new product that promises to revolutionise the retro computing world.

The One ROM, built with an RP2350 microcontroller, is a highly configurable and low-cost flexible ROM replacement for retro computers. Piers, who plays a central role in its development and maintenance, has employed a number of tricks to meet the performance requirements of the One ROM's firmware.

One of the key improvements in the One ROM is its 5V capability, making it suitable for replacing failing ROMs in old Commodore gear. This was made possible by the A4 stepping, which added 5V tolerance, allowing Piers to reformulate the One ROM's design.

Interestingly, the One ROM can emulate all three ROMs in the Commodore 64 (C64), including the basic ROM, kernel ROM, and character ROM, as demonstrated in a C64 demo.

Piers' video, serving as a valuable resource for understanding the design process and compromises made in the development of the One ROM, provides insights into the functional requirements and solutions implemented in the One ROM. The video offers a detailed look into the design process, highlighting the tradeoffs, compromises, and hacks made to meet the performance requirements.

The One ROM's code and the accompanying video from Piers can be found on GitHub, providing easy access for those interested in delving deeper into the project. The One ROM is built on a two-layer PCB and uses a cheap microcontroller, making it a cost-effective solution for retro computer enthusiasts.

However, the PCB layout for the RP2350 microcontroller in the One ROM required extensive changes compared to the larger STM32 in the previous version. The RP2350 microcontroller uses large power and ground pads underneath the IC, which previously served as an area for dropping vias to the other side of the board, but is no longer available for signal routing due to the size constraints of the board needing to fit in the original form factor used by the C64.

Despite these challenges, Piers has managed to create a product that not only meets the functional requirements but also offers a fascinating glimpse into the design process of a modern ROM replacement for retro computers. The One ROM is set to make a significant impact on the retro computing community, offering a highly configurable, low-cost, and performance-optimised solution for retro computer enthusiasts.