Article View: comp.arch
Article #11118Re: Relatively long cycle time in 486 LOOP instruction
From: Eliot Moss
Date: Thu, 17 Dec 1992 12:31
Date: Thu, 17 Dec 1992 12:31
16 lines
1590 bytes
1590 bytes
A guess as to why a decrement-and-branch instruction might take longer than you expect is that if the processor is pipelined, they may stall instruction issue until this instruction has resolved whether or not it is going to branch. I don't know the instruction set in detail, but if these are instructions where the branch target is in a register or computed (i.e., not absolute in the instruction, or PC relative), you can also lose cycles in getting the branch target fetched. -- J. Eliot B. Moss, Associate Professor Visiting Associate Professor Department of Computer Science School of Computer Science Lederle Graduate Research Center Carnegie Mellon University University of Massachusetts 5000 Forbes Avenue Amherst, MA 01003 Pittsburgh, PA 15213-3891 (413) 545-4206, 545-1249 (fax) (412) 268-6767, 681-5739 (fax) Moss@cs.umass.edu Moss@cs.cmu.edu
Technical Details
Message-ID:
<MOSS.92Dec17073124@CRAFTY.cs.cmu.edu>Path:
arc1-ca.pugleaf.net!sparky!uunet!usc!rpi!usenet.coe.montana.edu!news.u.washington.edu!ogicse!das-news.harvard.edu!cantaloupe.srv.cs.cmu.edu!netnews-2.srv.cs.cmu.edu!mossReferences:
<fWFHrqe@quack.sac.ca.us>Show Full Headers
Complete Article Headers
Path: arc1-ca.pugleaf.net!sparky!uunet!usc!rpi!usenet.coe.montana.edu!news.u.washington.edu!ogicse!das-news.harvard.edu!cantaloupe.srv.cs.cmu.edu!netnews-2.srv.cs.cmu.edu!moss From: moss@cs.cmu.edu (Eliot Moss) Newsgroups: comp.arch Subject: Re: Relatively long cycle time in 486 LOOP instruction Message-ID: <MOSS.92Dec17073124@CRAFTY.cs.cmu.edu> Date: 17 Dec 92 12:31:24 GMT Article-I.D.: CRAFTY.MOSS.92Dec17073124 References: <fWFHrqe@quack.sac.ca.us> Sender: news@cs.cmu.edu (Usenet News System) Reply-To: moss@cs.cmu.edu Organization: Dept of Comp and Info Sci, Univ of Mass (Amherst) Lines: 16 In-Reply-To: dfox@quack.sac.ca.us's message of 16 Dec 1992 06:02:51 UTC Nntp-Posting-Host: crafty.fox.cs.cmu.edu