Re: 64-bit embedded computing is here and now

From	Don Y <blockedofcourse@foo.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: 64-bit embedded computing is here and now
Date	2021-06-08 16:00 -0700
Organization	A noiseless patient Spider
Message-ID	<s9osrt$5fa$1@dont-email.me> (permalink)
References	<7eefb5db-b155-44f8-9aad-7ce25d06c602n@googlegroups.com> <87lf7kexbp.fsf@nightsong.com> <s9n10p$t4i$1@dont-email.me> <Iyz*Vc+ly@news.chiark.greenend.org.uk>

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On 6/8/2021 7:46 AM, Theo wrote:
> David Brown <david.brown@hesbynett.no> wrote:
>> But for microcontrollers - which dominate embedded systems - there has
>> been a lot to gain by going from 8-bit and 16-bit to 32-bit for little
>> cost.  There is almost nothing to gain from a move to 64-bit, but the
>> cost would be a good deal higher.  So it is not going to happen - at
>> least not more than a very small and very gradual change.
> 
> I think there will be divergence about what people mean by an N-bit system:
> 
> Register size
> Unit of logical/arithmetical processing
> Memory address/pointer size
> Memory bus/cache width

(General) Register size is the primary driver.

A processor can have very different "size" subcomponents.
E.g., a Z80 is an 8b processor -- registers are nominally 8b.
However, it support 16b operations -- on register PAIRs
(an implicit acknowledgement that the REGISTER is smaller
than the register pair).  This is common on many smaller
processors.  The address space is 16b -- with a separate 16b
address space for I/Os.  The Z180 extends the PHYSICAL
address space to 20b but the logical address space
remains unchanged at 16b (if you want to specify a physical
address, you must use 20+ bits to represent it -- and invoke
a separate mechanism to access it!).  The ALU is *4* bits.

Cache?  Which one?  I or D?  L1/2/3/?

What about the oddballs -- 12b?  1b?

> I think we will increasingly see parts which have different sizes on one
> area but not the other.
> 
> For example, for doing some kinds of logical operations (eg crypto), having
> 64-bit registers and ALU makes sense, but you might only need kilobytes of
> memory so only have <32 address bits.

That depends on the algorithm chosen and the hardware support available.

> For something else, like a microcontroller that's hung off the side of a
> bigger system (eg the MCU on a PCIe card) you might want the ability to
> handle 64 bit addresses but don't need to pay the price for 64-bit
> registers.
> 
> Or you might operate with 16 or 32 bit wide external RAM chip, but your
> cache could extend that to a wider word width.
> 
> There are many permutations, and I think people will pay the cost where it
> benefits them and not where it doesn't.

But you don't buy MCUs with a-la-carte pricing.  How much does an extra
timer cost me?  What if I want it to also serve as a *counter*?  What
cost for 100K of internal ROM?  200K?

[It would be an interesting exercise to try to do a linear analysis of
product prices with an idea of trying to tease out the "costs" (to
the developer) for each feature in EXISTING products!]

Instead, you see a *price* that is reflective of how widely used the
device happens to be, today.  You are reliant on the preferences of others
to determine which is the most cost effective product -- for *you*.

E.g., most of my devices have no "display" -- yet, the MCU I've chosen
has hardware support for same.  It would obviously cost me more to
select a device WITHOUT that added capability -- because most
purchasers *want* a display (and *they* drive the production economies).

I could, potentially, use a 2A03 for some applications.  But, the "TCO"
of such an approach would exceed that of a 32b (or larger) processor!

[What a crazy world!]

> This is not a new phenomenon, of course.  But for a time all these numbers
> were in the range between 16 and 32 bits, which made 32 simplest all round.
> Just like we previously had various 8/16 hybrids (eg 8 bit datapath, 16 bit
> address) I think we're going to see more 32/64 hybrids.
> 
> Theo
>

Thread

64-bit embedded computing is here and now James Brakefield <jim.brakefield@ieee.org> - 2021-06-07 07:47 -0700
  Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-07 14:13 -0700
  Re: 64-bit embedded computing is here and now Paul Rubin <no.email@nospam.invalid> - 2021-06-07 22:31 -0700
    Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-08 07:59 +0200
      Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 00:39 -0700
        Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-08 13:04 +0200
          Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 17:30 -0700
            Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-09 09:17 +0200
              Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 03:12 -0700
                Re: 64-bit embedded computing is here and now George Neuner <gneuner2@comcast.net> - 2021-06-12 12:58 -0400
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-12 12:40 -0700
              Re: 64-bit embedded computing is here and now Paul Rubin <no.email@nospam.invalid> - 2021-06-09 09:41 -0700
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 10:12 -0700
                Re: 64-bit embedded computing is here and now DJ Delorie <dj@delorie.com> - 2021-06-09 13:16 -0400
                Re: 64-bit embedded computing is here and now Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-09 13:44 -0400
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 22:03 +0300
                Re: 64-bit embedded computing is here and now Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-09 15:22 -0400
                Re: 64-bit embedded computing is here and now Paul Rubin <no.email@nospam.invalid> - 2021-06-09 12:58 -0700
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 16:26 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 23:12 +0300
        Re: 64-bit embedded computing is here and now James Brakefield <jim.brakefield@ieee.org> - 2021-06-08 12:38 -0700
          Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-08 22:11 +0200
            Re: 64-bit embedded computing is here and now James Brakefield <jim.brakefield@ieee.org> - 2021-06-08 14:25 -0700
            Re: 64-bit embedded computing is here and now George Neuner <gneuner2@comcast.net> - 2021-06-09 00:16 -0400
              Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-09 10:40 +0200
                Re: 64-bit embedded computing is here and now Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2021-06-09 22:52 +0200
                Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-10 09:37 +0200
          Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 01:01 +0300
            Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 18:29 -0700
              Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 20:56 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 17:12 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-10 13:45 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-10 06:55 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-10 18:32 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-10 14:09 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-11 01:13 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-10 21:55 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-11 14:14 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-11 05:10 -0700
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-11 16:35 +0300
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-11 16:24 -0700
              Re: 64-bit embedded computing is here and now George Neuner <gneuner2@comcast.net> - 2021-06-14 05:41 -0400
          Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 16:51 -0700
          Re: 64-bit embedded computing is here and now Paul Rubin <no.email@nospam.invalid> - 2021-06-08 18:20 -0700
            Re: 64-bit embedded computing is here and now Theo <theom+news@chiark.greenend.org.uk> - 2021-06-09 18:07 +0100
              Re: 64-bit embedded computing is here and now Paul Rubin <no.email@nospam.invalid> - 2021-06-09 10:34 -0700
                Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 16:37 -0700
              Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 16:43 -0700
      Re: 64-bit embedded computing is here and now Theo <theom+news@chiark.greenend.org.uk> - 2021-06-08 15:46 +0100
        Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-08 22:18 +0200
          Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-08 23:39 +0300
            Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 18:33 -0700
            Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-09 10:59 +0200
              Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 21:00 +0300
                Re: 64-bit embedded computing is here and now David Brown <david.brown@hesbynett.no> - 2021-06-09 20:55 +0200
                Re: 64-bit embedded computing is here and now Dimiter_Popoff <dp@tgi-sci.com> - 2021-06-09 22:06 +0300
        Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-08 16:00 -0700
          Re: 64-bit embedded computing is here and now Theo <theom+news@chiark.greenend.org.uk> - 2021-06-09 13:10 +0100
            Re: 64-bit embedded computing is here and now Don Y <blockedofcourse@foo.invalid> - 2021-06-09 06:19 -0700

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