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Re: Regarding branch delay instructions in R4000

To: Michael Uhler <uhler@mips.com>
Subject: Re: Regarding branch delay instructions in R4000
From: karthikeyan natarajan <karthik_96cse@yahoo.com>
Date: Sat, 20 Dec 2003 09:53:12 +0000 (GMT)
Cc: linux-mips@linux-mips.org
In-reply-to: <1071816092.30316.8.camel@gmu-linux>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Hi gmu,

    Have got a one more doubt...
MIPS stands for Microprocessor without Interlocked
Pipeline Stages.
    But, in the "R4400_Uman_book_Ed2.pdf" doc, it is
mentioned that the CPU general registers are 
interlocked. I am bit confused after reading this doc.
    Would be great if you clarify this doubt too...

Thanks much,
-karthi

> The MIPS architecture specifies a single delay slot
> after a branch
> or jump.  The fact that the R4000 implementation
> (and pretty much
> any of the ones following) had a pipeline in which
> more instructions
> had already entered the pipe before the branch is
> resolved is not
> relevant to the architecture specification.  In the
> case you
> mention, a single instruction is executed after the
> branch, as
> architecturally required, and any subsequent
> instructions in the
> pipe are killed.
> 
> /gmu
> 
> On Thu, 2003-12-18 at 22:01, karthikeyan natarajan
> wrote:
> > Hi All,
> > 
> >     If this is not a right forum to ask this
> Question,
> > 
> > please redirect me to the appropriate one...
> >     Since R4000 is using the 8 stage pipeline,
> three
> > instructions are already entered into the pipeline
> > when the branch instruction is executed. Out of
> these
> > three instructions, the first instruction will be 
> > executed for sure.
> > 
> > My question is:
> >     What happens to the other two instruction that
> are
> > in the delay slots? are they nullified?
> >     Could anyone please shed some light on this.
> > 
> > Thanks much,
> > -karthi
> > 
> > =====
> > The expert at anything was once a beginner
> > 
> >
>
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> -- 
> Michael Uhler, Chief Technology Officer
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=====
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