Date: Sun, 12 Nov 2006 23:53:12 +0000 From: Nicholas Clark <nick@ccl4.org> To: Olivier Houchard <mlfbsd@cognet.ci0.org> Cc: arm@freebsd.org, Giorgos Keramidas <keramida@freebsd.org>, Joseph Koshy <joseph.koshy@gmail.com> Subject: Re: [head tinderbox] failure on arm/arm Message-ID: <20061112235312.GV6501@plum.flirble.org> In-Reply-To: <20061112234412.GA12998@ci0.org> References: <20061112133929.9194773068@freebsd-current.sentex.ca> <20061112140010.GA47660@rambler-co.ru> <20061112144230.GC2331@kobe.laptop> <20061112145151.GC49703@rambler-co.ru> <20061112151150.GA2988@kobe.laptop> <84dead720611120758r4f1cc6e8l8ca4432ba56f3f7f@mail.gmail.com> <20061112170711.GQ6501@plum.flirble.org> <20061112233434.GA12739@ci0.org> <20061112232742.GU6501@plum.flirble.org> <20061112234412.GA12998@ci0.org>
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On Mon, Nov 13, 2006 at 12:44:12AM +0100, Olivier Houchard wrote: > On Sun, Nov 12, 2006 at 11:27:42PM +0000, Nicholas Clark wrote: > > On Mon, Nov 13, 2006 at 12:34:34AM +0100, Olivier Houchard wrote: > > > > > No, we're not using the mixed endian IEEE 64bits representation. We're > > > defaulting to softfloat VFP. What would be te point of switching ? > > > > >From my limited understanding of these things (mostly observing on the > > ARM Linux lists) absolutely none. The mixed endian IEEE representation > > is a complete pain, I'm unaware of any reason why it was chosen over a > > conventional little endian representation (probably back some time in > > 1987). > > > > I thought so :) > I think FPA is used for historical reasons, because that's what some older > arm cpus used when they had a FPU. And of course using a kernel FPE was a > great idea for linux too. But I think that the FPA (the external floating point unit) only was only actually produced to used with the 25 Mhz ARM 3s (*), which I think was 1990 or so, which I think would be the first time that mixed endian layout was set in silicon. But the mixed endian layout would have had to have been chosen before RISC OS 2 shipped in 1989, as it had bundled applications written in C, which uses the (emulated) floating point instructions. Hence as far as I know there was no hardware reason to choose that layout - hardware came later. Nicholas Clark * because at the time I upgraded my parents' Archimedes to an ARM 3, I asked about this, and the 30 Mhz CPU-on-a-daughterboards then available would not suitable for adding an FPA, not that it mattered, as the run of FPAs was now all sold)
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