The kernal of REX source code is now available on both the Diablo LU0 and LU7 in the downloads section.
This is interesting reading for anyone who wants to know how IRIS did its thing internally.
This includes memory locations 0-177 and 600-7777, the heart of IRIS. What is NOT included is SIR (system initialization routine) or DBUG (a memory-resident process similar to DSP) both of which are embedded in the IRIS REX file.
The source was reverse engineered from a DSP listing of REX. But In order to provide a fresh assembly listing of the source, it was necessary to update the assembler ASM.
Turns out that ASM reads the data blocks directly from a source text file, rather than use READITEM to read line by line. However, it does not have the logic for extended textfiles, which is any file over 128 data blocks, or 64KB of text. REX was way past that.
So ASM was modified to work with extended files as well, and that version is called ASMX. The new version also suppressed the form-feed and headings that ASM puts out every 59 lines. That makes it easier to read the listing in modern text editors.