Am Samstag, 27. November 2010, 18:16:05 schrieb Chris Tyler: > So I've had a number of conversations with Dennis Gilmore and folks from > other ARM disro ports about v7 support, and particularly with respect to > hardware math. (In addition, one of the Seneca students is currently > investigating v5 vs. v7 support in an attempt to figure out how much of > the Fedora universe needs to be recompiled for optimal benefit). > > Regarding hardfp, though, things are quite unclear. My understanding of > soft/softfp/hardfp was initially wrong. As I understand it now: > > - soft does all the math in software. Function values are passed in CPU > registers where appropriate. > - softfp enables the use of FPU instructions, but continues to pass > function arguments in CPU registers. This mode enables hardware > acceleration of math and interoperability with soft, at the cost of a > CPU->FPU register move in some cases. > - hardfp enables the use of FPU instructions, and function values are > passed in FPU registers where appropriate. This mode is incompatible > with soft and softfp, and cannot be used on CPUs that have an FPU. ... and cannot be used on CPUs that have _no_ FPU (probably same for specialized/external FPU). > According to gcc (docs + error messages), it is also incompatible with > CPUs that use a "vfp" math unit, such as OMAP3xxx CPUs (BeagleBoard) and > (I think) the CPU used in the XO1.75. I'm unclear on which hardware math > units it is compatible with. Hmm, really ? There are different vfp versions (vfp/vfp2/vfp3 and vfp4 upcoming). >From what I see and what was discussed at MeeGo Conference, the least common denominator is hardfp with vfpv3-d16. See: * http://lists.meego.com/pipermail/meego-sdk/2010-November/000449.html * http://wiki.debian.org/ArmHardFloatPort * https://wiki.linaro.org/Linaro-arm-hardfloat > > In terms of hardware support, I think we definitely want to continue to > support armv5tel with software floating-point, since that's what is used > on many current Marvell CPUs, including those used in the > SheevaPlug/GuruPlug/OpenRD. > > hardfp would break compatibility with all of the existing binary > packages, and hardfp can't be compiled by gcc for any of the CPUs I have > got my hands on so far. > > Thus, I recommend that we aim at armv7l softfp to support as an arch > alongside armv5tel. I still think a armv7 hardfloat little with vfpv3-d16 would be a good baseline. Best, Jan-Simon _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
