brownell@harvard.ARPA (Dave Brownell) (08/16/84)
[Headline: "Mac II with 68020 outperforms VAX 11/780!!"]
The CALLM instruction on the 68020 has some rather intriguing looking
features; I'm wondering if any hardware wizards have looked at it
with any thought to designing a nifty object oriented 68020 machine.
A brief summary of what happens -- user issues a CALLM instruction,
referencing a module descriptor which we'll assume resides in protected
memory. This activates (optionally) access level updating hardware,
which is external to the 68020. (256 access levels, meaning determined
solely by hardware.) The external hardware may allow the increase in
access level, or refuse it (in which case you get a "format error"
exception). If the CALLM is successful, a special stack frame is
created and additional magic may happen. RETM undoes all this.
I'm no expert on capability based architectures, or on object based
architectures, but I don't think I'm far off in thinking this is what
Motorola has in mind. Is someone out there who could give an example
of how these features might be used? Got any suggestions for books/articles
to read?
Dave Brownell
Sequoia Systems Inc.
{allegra,floyd,ihnp4,seismo}!harvard!sequoia!brownell