In this video, my trusty Commodore 64 rewrites its own kernal ROM, and I demonstrate how easy it is to build applications that monitor ROM activity using One ROM, the most flexible replacement ROM for your retro system.

Plugins covered:

  • C64 Kernal Mod. A C64 modifies its own kernal with 78 bytes of machine code, and a 116 line One ROM plugin.
  • C64 Character Monitor. One ROM monitors every VIC-II character read, and toggles the status LED in response to a specific character being displayed.

🔗 Links

Discord: https://discord.gg/tq22nJefXr
Buy: https://onerom.org/buy
One ROM Plugin API: https://github.com/piersfinlayson/one-rom/blob/main/sdrr/ora/api.h

⏰ Timestamps

00:00 Introduction
01:02 Demo - C64 rewriting the ROM
03:11 Demo - Character Monitor
04:10 Code - Character Monitor plugin
09:08 Code - Kernal Mod plugin
12:45 Code - Kernal Mod C64 assembly
15:51 Wrap up

Video content copyright (c) 2026 piers.rocks Limited. All rights reserved.

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