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From: tim@crackle.amd.com (Tim Olson)
Newsgroups: comp.arch
Subject: Re: RISC & context switches
Message-ID: <24431@amdcad.AMD.COM>
Date: 13 Feb 89 19:46:26 GMT
References: <784@atanasoff.cs.iastate.edu> <7239@june.cs.washington.edu> <89Feb12.125852est.10867@ephemeral.ai.toronto.edu> <1101@wasatch.UUCP>
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In article <1101@wasatch.UUCP> moore%cdr.utah.edu.UUCP@wasatch.UUCP (Tim Moore) writes:
| In article <89Feb12.125852est.10867@ephemeral.ai.toronto.edu> bradb@ai.toronto.edu (Brad Brown) writes:
| 
| )There is a somewhat related problem when you make a subroutine call --
| )the calling function usually has to save its registers so it gets it's
| )"context" restored when the function returns.  Machines like MIPS have
| )made use of their very large number of registers (192?) by having a pointer
| )to one of the registers that is effectively the base pointer for the
| )stack of registers that the currently executing function can use.
| 
| You're confusing MIPS and SPARC here. The MIPS chips have a fairly
| conventional set of general registers; SPARC has a large file of
| registers that are divided into "windows" in the manner you describe.

I think he was talking about the Am29000 (192 registers).  The 29k has
64 globals and 128 locals, all of which are accessible by the
instructions.  An internal stack pointer allows a register-window
implementation that uses variable-sized windows (tailored to the size of
each individual function's needs), rather than the fixed-sized windows
of the SPARC.


	-- Tim Olson
	Advanced Micro Devices
	(tim@crackle.amd.com)