Software Defined ROM's Newest Version: One ROM Unveiled
In a recent development, a developer known as [Piers] has unveiled the latest version of the One ROM, a compact solution designed to breathe new life into old Commodore gear. The One ROM is built on a two-layer PCB and uses a cost-effective microcontroller, the RP2350.
The One ROM is not just a replacement for failing ROMs in vintage Commodore equipment; it also emulates the basic ROM, kernel ROM, and character ROM in a Commodore 64 (C64). Given the performance-critical nature of the One ROM's firmware, [Piers] employs a number of tricks to meet its speed requirements.
One of the challenges faced by [Piers] was the size constraints of the original form factor used by the C64. The RP2350, while offering several advantages, uses large power and ground pads underneath the IC, making the area originally used for signal routing unavailable. To overcome this, the PCB layout for the RP2350 required extensive changes from the larger STM32 used in the previous version.
Despite these challenges, the One ROM's design no longer requires 23 level shifters due to the A4 stepping. This not only makes the One ROM 5V capable but also allows it to fit on a smaller board.
The One ROM's firmware is crucial in converting requests quickly, a task it handles efficiently. For those interested in delving deeper into the design process and the trade-offs made in the project, an accompanying video from [Piers] provides valuable insights.
The One ROM code is now available on GitHub, allowing enthusiasts and developers to tinker and contribute to this exciting project. With the One ROM, old Commodore gear can now perform as good as new, providing a new lease of life for these vintage machines.
