From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by oss.sgi.com (8.11.3/8.11.3) id f2GHrU910424 for linux-mips-outgoing; Fri, 16 Mar 2001 09:53:30 -0800 Received: from dea.waldorf-gmbh.de (u-210-18.karlsruhe.ipdial.viaginterkom.de [62.180.18.210]) by oss.sgi.com (8.11.3/8.11.3) with ESMTP id f2GHrRM10417 for ; Fri, 16 Mar 2001 09:53:27 -0800 Received: (from ralf@localhost) by dea.waldorf-gmbh.de (8.11.1/8.11.1) id f2GE4NL04861; Fri, 16 Mar 2001 15:04:23 +0100 Date: Fri, 16 Mar 2001 15:04:23 +0100 From: Ralf Baechle To: "Kevin D. Kissell" Cc: Subject: Re: Can't build a CONFIG_CPU_NEVADA kernel Message-ID: <20010316150423.A3529@bacchus.dhis.org> References: <20010314084633.A25674@nevyn.them.org> <20010314195919.A1911@bacchus.dhis.org> <20010314140529.A29525@nevyn.them.org> <20010314202058.B1911@bacchus.dhis.org> <00fc01c0acd3$c881ca80$0deca8c0@Ulysses> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <00fc01c0acd3$c881ca80$0deca8c0@Ulysses>; from kevink@mips.com on Wed, Mar 14, 2001 at 11:11:47PM +0100 X-Accept-Language: de,en,fr Sender: owner-linux-mips@oss.sgi.com Precedence: bulk On Wed, Mar 14, 2001 at 11:11:47PM +0100, Kevin D. Kissell wrote: > > Don't think of the r8000; the kernel only uses the -mcpu=r8000 option > > because the Nevada CPUs have _somewhat_ similar scheduling properties > > to the R8000. This of it as an independant ISA expension which can > > be used with an arbitrary MIPS processor - even a R3000 processor. > > In the interests of historical accuracy and general pedantry, > let me point out that -mcpu=r8000 is in effect a rather klugy > way of saying "-mips4" to compilers that predate official > MIPS IV ISA support. The R8000 was the first MIPS IV > CPU, followed by the R10000 and the R5000. The "Nevada" > processors added three implementation specific instructions > to the MIPS IV ISA: MAD, MADU, and MUL (targeted multiply). > "Correct" usage would be to enable those three instructions > with a "-mcpu=nevada", or better still, "-mcpu=r5200" (for > consistency), and to enable the rest of the MIPS IV ISA > with "-mips4" instead of the archaic r8000 hack. Your historic facts may be right but the GCC fact aren't. -mcpu=xxx tell GCC to schedule instructions for a certain processor xxx. This does not enable the full use of it's instruction set. Back in time when I choose these options I choose because GCC didn't know -mcpu=r5000 but the R8000 was supported and it was the closest fit. Gcc 1.1.2 knows this option so I just changed all instances of -mcpu=r8000 into -mcpu=r5000. > Note, furthermore, that -mmad needs to be handled with care: > Prior to MIPS standardizing the instruction as part of > MIPS32, there were four or five subtly (or not so subltly) > different definitions of integer multiply-accumulate for MIPS. > Most use the same opcode, but even those can differ in side > effects (is the rd field interpreted, etc.). A R4650 madd operation > will probably behave equivalently on a Nevada CPU, > but certainly not on a Vr41xx part, for example. Unfortunately true but there is a reason that QED's manual marks it as an proprietary extension ... Ralf From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 16 Mar 2001 15:04:23 +0100 From: Ralf Baechle Subject: Re: Can't build a CONFIG_CPU_NEVADA kernel Message-ID: <20010316150423.A3529@bacchus.dhis.org> References: <20010314084633.A25674@nevyn.them.org> <20010314195919.A1911@bacchus.dhis.org> <20010314140529.A29525@nevyn.them.org> <20010314202058.B1911@bacchus.dhis.org> <00fc01c0acd3$c881ca80$0deca8c0@Ulysses> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00fc01c0acd3$c881ca80$0deca8c0@Ulysses>; from kevink@mips.com on Wed, Mar 14, 2001 at 11:11:47PM +0100 Sender: owner-linux-mips@oss.sgi.com To: "Kevin D. Kissell" Cc: linux-mips@oss.sgi.com Message-ID: <20010316140423.2kQnGg66Gl6ZPcovhVglPdU6rrbviU3Ve7a3EfyDDqg@z> On Wed, Mar 14, 2001 at 11:11:47PM +0100, Kevin D. Kissell wrote: > > Don't think of the r8000; the kernel only uses the -mcpu=r8000 option > > because the Nevada CPUs have _somewhat_ similar scheduling properties > > to the R8000. This of it as an independant ISA expension which can > > be used with an arbitrary MIPS processor - even a R3000 processor. > > In the interests of historical accuracy and general pedantry, > let me point out that -mcpu=r8000 is in effect a rather klugy > way of saying "-mips4" to compilers that predate official > MIPS IV ISA support. The R8000 was the first MIPS IV > CPU, followed by the R10000 and the R5000. The "Nevada" > processors added three implementation specific instructions > to the MIPS IV ISA: MAD, MADU, and MUL (targeted multiply). > "Correct" usage would be to enable those three instructions > with a "-mcpu=nevada", or better still, "-mcpu=r5200" (for > consistency), and to enable the rest of the MIPS IV ISA > with "-mips4" instead of the archaic r8000 hack. Your historic facts may be right but the GCC fact aren't. -mcpu=xxx tell GCC to schedule instructions for a certain processor xxx. This does not enable the full use of it's instruction set. Back in time when I choose these options I choose because GCC didn't know -mcpu=r5000 but the R8000 was supported and it was the closest fit. Gcc 1.1.2 knows this option so I just changed all instances of -mcpu=r8000 into -mcpu=r5000. > Note, furthermore, that -mmad needs to be handled with care: > Prior to MIPS standardizing the instruction as part of > MIPS32, there were four or five subtly (or not so subltly) > different definitions of integer multiply-accumulate for MIPS. > Most use the same opcode, but even those can differ in side > effects (is the rd field interpreted, etc.). A R4650 madd operation > will probably behave equivalently on a Nevada CPU, > but certainly not on a Vr41xx part, for example. Unfortunately true but there is a reason that QED's manual marks it as an proprietary extension ... Ralf