Dennis Lee Bieber  wrote:
> On Sat, 29 Jun 2019 19:24:18 +0100, Folderol 
> declaimed the following:
>
>>
>> This really surprises (and disappoints) me. The debian base is capable of
all
>> sorts of processor optimisations, and the people doing the Pi have the
>> advantage of knowing *exactly* what differences there are between models.
>
>  And would have to maintain different downloads/builds confusing
> neophytes. They already have to create a build different from pure Debian.
> Debian has ARMEL, ARMHF, and 64-bit. The ARMHF is for devices for v7 ARM
> architecture and a hardware floating point (VFP3, as I recall) -- but
> Raspbian isn't the exact same...
>
> https://wiki.debian.org/ArmPorts
> """
> Raspbian - Uses the hard-float version of the "new" ABI (EABI) like Debian
> armhf but targets v6 rather than v7. Currently tracks Debian jessie and
> stretch. Primarily but not exclusively targeted at the Raspberry Pi. GNU
> Triplet: arm-linux-gnueabihf
> """
>
> ARM v6 has a different...
>
> https://en.wikipedia.org/wiki/ARM_architecture
> """
> VFPv2
>     An optional extension to the ARM instruction set in the ARMv5TE,
> ARMv5TEJ and ARMv6 architectures. VFPv2 has 16 64-bit FPU registers.
>
> VFPv3 or VFPv3-D32
>     Implemented on most Cortex-A8 and A9 ARMv7 processors. It is backwards
> compatible with VFPv2, except that it cannot trap floating-point
> exceptions. VFPv3 has 32 64-bit FPU registers as standard, adds VCVT
> instructions to convert between scalar, float and double, adds immediate
> mode to VMOV such that constants can be loaded into FPU registers.
>
> VFPv3-D16
>     As above, but with only 16 64-bit FPU registers. Implemented on
> Cortex-R4 and R5 processors and the Tegra 2 (Cortex-A9).
> """

The work involved to maintain two concurrent releases (with a lot of
customisations) is their main reason apparently, yes, while the vast
majority of the install base (the Pis out there) isn't 64 bit compatible.
But their main software man also keeps saying: give me one good reason why
64 bit is better than 32. See their blog on the new Buster release. Well,
it gets a bit embarrassing with lost optimisations when the current chip is
armv8, for crying out loud. He says it doesn't make a difference but I
wonder.

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