If you are interested to start a homebrew project on CD-i, one of the things you want to do is understanding the CD-i's operating system: Microware's OS-9.
The first version ("OS-9 Level One"), which dates back to 1979–1980, was written in assembly language for the Motorola 6809 CPU, and all of its processes ran within the 64KB address space of the CPU without a memory management unit. In 1983, OS-9/6809 was ported to Motorola 68000 assembly language. In mid 1980s, OS-9 was selected for the CD-i operating system. Around the same time, Microsoft approached Microware for acquisition of the company primarily because it was attracted by CD-RTOS, the CD-i operating system. The negotiation failed and no deal was made; Microware decided to remain independent. The best known hardware (due to its low price and broad distribution) was the TRS-80 Color Computer (CoCo) and the similar Dragon series. This Tandy CoCo might be one of the very few consumer editions of OS-9. The benefit behind this is that the CoCo archive holds a large archive of OS-9 material.
While the CoCo uses the 8-bit version of OS-9, this info is very valuable for anyone who wants to develop on CD-i and wants to know more of CD-i's OS-9 operating system.
In this OS-9 Projects archive, you can find the following documents:
[Thanks, OS-9 Projects, CoCo Archive, CD-i Fan, Jorg Kennis]