From: Grant Grundler <grundler@cup.hp.com>
To: Ryan Bradetich <rbradetich@uswest.net>
Cc: Parisc Linux <parisc-linux@thepuffingroup.com>
Subject: Re: [parisc-linux] Questions understanding exec_kernel
Date: Tue, 21 Sep 1999 21:26:50 -0700 [thread overview]
Message-ID: <199909220426.VAA27105@milano.cup.hp.com> (raw)
In-Reply-To: Your message of "Tue, 21 Sep 1999 19:12:06 PDT." <37E82CE6.3A5DFFB0@uswest.net>
Ryan Bradetich wrote:
> [Question: Page 5-149 from the PA-RISC 1.1 Architecture and Instruction
> Set Reference Manual states: "Level 0: If the target control register
> is CR 8, 9, 12, 13, 17, or 20, this instructin executes as a null
> instruction." I am assuming we are running at level 0 since the rfi
> command required running at level 0, so what is the difference between a
> null instruction and a nop?]
That's an easy one:
Nullfied instructions are simple ignored - output discarded.
Branch instructions have a "nullify" flag - the PA1.1 book
probably talks more about details here.
NOP is an instruction which is executed but does nothing useful.
(eg OR R0, R0, R0) Often used to get precise timing in a loop
or patch out unwanted instructions for self modifing code.
Someone else will have to tackle the RFI question....
grant
next prev parent reply other threads:[~1999-09-22 4:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-09-22 1:12 [parisc-linux] Questions understanding exec_kernel Ryan Bradetich
1999-09-22 4:26 ` Grant Grundler [this message]
1999-09-22 6:45 ` [parisc-linux] C360 boot problem Hannu Martikka
1999-09-22 13:34 ` Philipp Rumpf
1999-09-22 13:32 ` [parisc-linux] Questions understanding exec_kernel Philipp Rumpf
1999-09-22 12:46 ` Hai Vo-Ba
1999-09-22 13:36 ` Philipp Rumpf
1999-09-22 13:29 ` Philipp Rumpf
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