When flag REG_VMIO is set, printing/parsing are done through the user-supplied print/parse routines, a special switch is set, and the normal UNIT pointer argument is left as null.

For the REG_VMIO case ONLY, scp could fill in the UNIT pointer argument with a pointer to the register data structure (cast to pointer to unit), which would allow fprint/fparse to know what register is being referenced and to pick up any additional information that might be necessary for printing and parsing, including flags added to their proper spot, the flags field.

The problem, of course, is that (REG *(UNIT *(reg structure)) may not be idempotent on some hosts (like word-oriented machines), not that many of these exist anymore. However, I think it's cleaner, in general, to put flags where they belong and find a way to let the print/parse routines know what register they're working on if REG_VMIO is set.

/Bob
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