850 IMMR SPR?

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I'm trying to make some sense out of a machine apparently based on the
850, with an eye to eventually getting NetBSD on it.  I found
http://fnapcf.fnal.gov/~ron/doc/motorola/PPC-see/850um_2.pdf, which
describes much of the 850, but I'm seeing code accessing SPR 638.
Table 4-9 (on page 4-9) in that PDF includes an entry for register 639,
calling it the IMMR.  It refers to "Section 10.4.1", which is not
present in the PDF as far as I can tell.

I've been noodling around trying to find stuff on the Web, with no
success (not surprising; using the Web is difficult and unpleasant for
me, so I'm not much good at it).  Anyone know where I could find the
rest of the document that 850um_2.pdf is apparently just a part of, or
any other reasonably complete documentation on the 850?  Failing that,
is there by any chance someone up for explaining the IMMR and how it
works?

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