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From: mslater@cup.portal.com (Michael Z Slater)
Newsgroups: comp.sys.mips
Subject: Re: What are the new features in MIPS-II instruction set?
Message-ID: <38533@cup.portal.com>
Date: 27 Jan 91 18:03:45 GMT
References: <k2.664739175@woodstock>
Organization: The Portal System (TM)
Lines: 24

>I'm interested in the differences between MIPS-I and MIPS-II
>instruction sets. The assembler manual doesn't mention it.
>Are there any advantages compiling a program with "-mips2"
>for the CD4680 (RC6280)?

I assume someone from MIPS will answer in more detail, but here's a quick
summary.

Loads are interlocked; you don't need a no-op if the next instruction uses
the data from the load.

Annulling branches and conditional traps are added.

FP additions include 64-bit load and store, square root, and float-to-fixed
conversion with rouding mode (ceiling, floor, etc.) explicitly specified.

Code should be faster and smaller if compiled for the MIPS-II instructions set,
but of course it won't work on anything but an R6000-based machine. I expect
double-precision FP code would see the biggest improvement.

Rumors are that the R4000 will support the same MIPS-II instructions, but it's 
going to be a while before you see R4000-based machines.

Michael Slater, Microprocessor Report   mslater@cup.portal.com