Re: Broadcom BCM2709, ARMv8, and missing CPU features

[Alan Corey <alan01346@gmail.com>]

Are you sure they don't boot?  Something in the way you need to set up
your HDMI changed, the video mode I had set on my B didn't work on my
3B so I got a blank screen.  Watch your LEDs, if they're flickering
it's booting.  I had a post on it at
https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=146684&p=966321#p966321
 I was able to boot into 640x480 mode once I edited my
/boot/config.txt on a different machine.

There are only 2 Raspbian images in their download area, one with X,
Mathematica, Libre Office, the works, and a "Lite" image with no X.
They still support all models with those images.  And they've sold
over 8 million of them.

I don't think I use big enough numbers to need 64 bit really, it's
more appealing to load 8 characters at once.  I'm not planning a Mars
mission.  If I can't fsck a 1 TB drive that's a problem.

freebie# calc '2^32'
        4294967296
freebie# calc '2^64'
        18446744073709551616



On 7/28/16, Lennart Sorensen <lsorense@csclub.uwaterloo.ca> wrote:
> On Thu, Jul 28, 2016 at 12:22:23PM -0400, Alan Corey wrote:
>> Huh?  I thought they claimed they were interchangeable.  I had an
>> image from my model B days 3 years ago that I booted on my 3B.  And I
>> cloned a working current 3B SD card and booted a Zero from it.  There
>> isn't a different Debian image for every brand of motherboard and CPU,
>> they probe to see what hardware is there.  I wouldn't expect older
>> images to contain drivers for newer hardware maybe.
>>
>> I guess I wouldn't make too much of the jump to 64 bit just yet.  I
>> remember when i386 jumped to 32 bit.  16 bit had a messy segmented
>> memory addressing scheme I was glad to get away from.  I can't afford
>> more than 32 bits worth of RAM anyway, especially since I've usually
>> got about 4 machines running.
>
> Well it isn't actually just a question of memory (most 8bit CPUs had 16
> bit address space, and many 16 bit CPUs had 24 or 32 bit address space,
> and some 32 bit x86 and arm chips can do 36 or 40 bit address space
> physically).  What you often gain going to a 64 bit CPU is the ability
> to do 64 bit arithmetic in one instruction, and store the variables
> in one register rather than two, rather than a bunch of stuff the
> compiler generates for you.  After all if you take two 64 bit integrs
> and try to multiply them on a 32 bit CPU, most of the time you end up
> with numerous multiply, shift, add, mask, instructions to implement
> the calculation using 32 bit only instructions, while on a 64 bit CPU
> usually it is just one instruction.  So the 64 bit CPU will probably do
> the calculation faster than the 32 bit CPU.  Of course if you only need
> 32 bit calculations, then it doesn't matter, so in many cases it isn't an
> issue, but when it matters it can really make a difference in performance.
>
> --
> Len Sorensen
>


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