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Groups > comp.lang.forth > #18949

Re: Parallax Propeller

From Les Cargill <lcargill99@comcast.com>
Newsgroups comp.lang.forth, comp.arch.embedded
Subject Re: Parallax Propeller
Date 2013-01-20 18:08 -0600
Organization A noiseless patient Spider
Message-ID <kdi0p6$9ta$1@dont-email.me> (permalink)
References (5 earlier) <qvvjf81u8h341ng3ndmnq48egqhqjf5r9f@4ax.com> <alv9l0Fq8aaU1@mid.individual.net> <tZidnZg9_bafW2fNnZ2dnUVZ8radnZ2d@lyse.net> <kdeuuv$qta$1@dont-email.me> <J5CdnSFtEvLW22HNnZ2dnUVZ8rOdnZ2d@lyse.net>

Cross-posted to 2 groups.

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David Brown wrote:
> On 19/01/13 21:18, Les Cargill wrote:
>> David Brown wrote:
>>> (Please do not snip newsgroups by using "followup to", unless the post
>>> really is off-topic in a group.)
>>>
>>>
>>> On 19/01/13 11:06, Paul E. Bennett wrote:
>>>> Ben Bradley wrote:
>>>>
>>>>> U=In comp.lang.forth,comp.arch.embedded On Sun, 13 Jan 2013 13:55:22
>>>>> GMT, Peter Jakacki <peterjakacki@gmail.com> wrote:
>>>>
>>>> [%X]
>>>>
>>>>>> The P2 which is due to be released soon
>>>>>
>>>>> ... still has zero interrupts.
>>>>>
>>>>> Yes, I first saw the propellor mentioned years ago, the 8 32-bit cores
>>>>> thing sounds nice, but no interrupts was a deal killer for me. A year
>>>>> or two back (with maybe earlier mention of the P2) I looked on the
>>>>> "official" support/discussion forums for the Propellor and saw this
>>>>> longish thread on "why doesn't it have interrupts" and there were
>>>>> posts there that covered every objection I've had or seen to a
>>>>> microcontroller not having interrupts, even  "why not add interrupts?
>>>>> It would take very little silicon and you don't have to use 'em if you
>>>>> don't want to." It's against that designer guru guy's religion or
>>>>> something.
>>>>>
>>>>> As far as I know there's no other microcontroller that doesn't have
>>>>> interrupts, and I can't recall one that didn't. The Apple ][ didn't
>>>>> use interrupts even though the 6502 had them. Maybe there were some
>>>>> 4-bit microprocessors that didn't have any interrupts.
>>>
>>> Were there not small Microchip PIC devices without interrupts?  The
>>> PIC12 series, or something like that (I didn't use them myself).
>>>
>>>>
>>>> One question you should ask yourself is why you think a parallel
>>>> processor
>>>> (particularly the mesh organised ones) really need to include
>>>> interrupts.
>>>> You have many processors, all the same, simple, no frills. You can
>>>> afford to
>>>> dedicate a processor to deal with inputs that need to be responded to
>>>> rapidly without the need for interrupts. I know that, to some, it
>>>> might seem
>>>> a waste of a processor, but with heavily parallel chips you could
>>>> afford to
>>>> think about how you allocate I/O around the processor array.
>>>>
>>>
>>> That argument might have merit /if/ this chip had many processors.  It
>>> only has 8.  I think the idea of splitting a design into multiple
>>> simple, semi-independent tasks that all work on their own
>>> cpu/core/thread, in their own little worlds, is very elegant.  It can
>>> give great modularisation, re-use of software-components, and easy
>>> testing.  But you need /many/ more than 8 threads for such a system with
>>> real-world programs - otherwise you have to combine tasks within the
>>> same thread, and you have lost all the elegance.
>>>
>>
>> You can still design them as if they were in their own thread and
>> run them in "series". The now-old CASE tool ObjecTime  had a separate
>> set of screen widgets for organizing separate "executables" into
>> threads.
>>
>> In non-case-tool systems, you simply run them one after the other.
>> This can be round-robin or through a more sophisticated arrangement.
>>
>
> You can certainly do that - but then you don't get the dedication of a
> core that lets you get low-latency reactions.
>

To be sure.

>>> So then you might have a system with lots more cores - say 64 cores.
>>> Then you have enough to do quite a number of tasks.  But to get that
>>> with a realistic price, power and size, these cores will be very simple
>>> and slow - which means that you can't do tasks that require a single
>>> core running quickly.
>>>
>>> What makes a lot more sense is to have a cpu that has hardware support
>>> for a RTOS, and is able to switch rapidly between different tasks.
>>
>> An RTOS can also be a purely software object. Do mean essentially
>> register bank switching?
>
> Bank switching is part of it, but to make a "hardware RTOS" you need a
> system to switch tasks (register banks) automatically by task.
>

I presume the code store is shared, so it's matter
of assigning the "task" represented by entry point <x> to
core <y>.

>>
>>> That
>>> way demanding tasks can get the cpu time they need, while you can also
>>> have lots of very simple tasks that give you the modularisation in code
>>> without having to dedicate lots of silicon.  The XMOS does a bit of
>>> this, in that it has 8 threads per cpu that can run up to 100 MIPS each
>>> (IIRC), but with a total of 500 MIPS per cpu, and it also has
>>> inter-process communication in hardware.
>>>
>>>
>>
>> Shared memory has been around since System V, so...
>
> There is a lot more to inter-process communication than shared memory.
> The XMOS implements a message passing system with CSP-style
> synchronisation.
>

Very nice indeed, then. CSP is the right abstraction.

>>
>>>> Check back in the history of processors and you will see why the
>>>> interrupt
>>>> was thought to be necessary in the first place. With the world
>>>> heading to
>>>> the much more use of multi-parallel processor I suspect the need for
>>>> interrupts will wane.
>>>>
>>>
>>> Look how many interrupts a modern PC or large embedded system has - they
>>> outnumber the number of cores by 50 to 1 at least.  Interrupts are not
>>> going away.
>>>
>>
>

-- 
Les Cargill

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Thread

Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-13 06:37 +0000
  Re: Parallax Propeller MK <mk@nospam.co.uk> - 2013-01-13 10:26 +0000
    Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-13 12:22 +0000
      Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-13 07:24 -0600
        Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-13 13:55 +0000
          Re: Parallax Propeller mhx@iae.nl (Marcel Hendrix) - 2013-01-13 17:13 +0200
            Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-16 06:23 -0600
              Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 15:01 +0000
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-16 09:12 -0600
                Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 15:36 +0000
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-16 10:59 -0600
                Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 23:38 +0000
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-17 04:04 -0600
                Re: Parallax Propeller Mark Wills <forthfreak@gmail.com> - 2013-01-17 04:52 -0800
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-01-24 22:48 -0800
                Re: Parallax Propeller Mark Wills <forthfreak@gmail.com> - 2013-01-24 23:10 -0800
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-01-28 17:42 -0800
                Re: Parallax Propeller "Rod Pemberton" <do_not_have@notemailnotz.cnm> - 2013-02-05 06:05 -0500
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-02-05 08:41 -0600
                Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-02-05 10:21 -0800
                Re: Parallax Propeller Bernd Paysan <bernd.paysan@gmx.de> - 2013-02-05 21:37 +0100
                Re: Parallax Propeller "Elizabeth D. Rather" <erather@forth.com> - 2013-02-05 10:44 -1000
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-02-05 15:52 -0600
                Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-02-06 00:29 -0800
                Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-02-06 00:31 -0800
                Re: Parallax Propeller Bernd Paysan <bernd.paysan@gmx.de> - 2013-02-06 19:46 +0100
                Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-02-09 00:11 -0800
                Re: Parallax Propeller anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-02-09 10:25 +0000
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-02-06 18:26 -0800
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-02-05 15:07 -0800
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-02-05 15:49 -0800
                Re: Parallax Propeller "Rod Pemberton" <do_not_have@notemailnotz.cnm> - 2013-02-05 06:04 -0500
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-02-05 15:21 -0800
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-16 18:09 -0500
          Re: Parallax Propeller Ben Bradley <ben_u_bradley@etcmail.com> - 2013-01-18 21:07 -0500
            Re: Parallax Propeller "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-01-19 10:06 +0000
              Re: Parallax Propeller Arlet Ottens <usenet+5@c-scape.nl> - 2013-01-19 13:04 +0100
              Re: Parallax Propeller "A. K." <akk@nospam.org> - 2013-01-19 13:22 +0100
                Re: Parallax Propeller Bernd Paysan <bernd.paysan@gmx.de> - 2013-01-19 13:38 +0100
              Re: Parallax Propeller David Brown <david.brown@removethis.hesbynett.no> - 2013-01-19 17:12 +0100
                Re: Parallax Propeller albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-01-19 16:45 +0000
                Re: Parallax Propeller David Brown <david.brown@removethis.hesbynett.no> - 2013-01-20 17:49 +0100
                Re: Parallax Propeller upsidedown@downunder.com - 2013-01-19 20:54 +0200
                Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-01-19 11:04 -0800
                Re: Parallax Propeller upsidedown@downunder.com - 2013-01-19 23:05 +0200
                Re: Parallax Propeller Mark Wills <markrobertwills@yahoo.co.uk> - 2013-01-20 01:05 -0800
                Re: Parallax Propeller Arlet Ottens <usenet+5@c-scape.nl> - 2013-01-20 12:11 +0100
                Re: Parallax Propeller upsidedown@downunder.com - 2013-01-20 13:53 +0200
                Re: Parallax Propeller upsidedown@downunder.com - 2013-01-20 13:26 +0200
                Re: Parallax Propeller Les Cargill <lcargill99@comcast.com> - 2013-01-19 14:23 -0600
                Re: Parallax Propeller Les Cargill <lcargill99@comcast.com> - 2013-01-19 14:18 -0600
                Re: Parallax Propeller David Brown <david.brown@removethis.hesbynett.no> - 2013-01-20 20:32 +0100
                Re: Parallax Propeller Les Cargill <lcargill99@comcast.com> - 2013-01-20 18:08 -0600
                Re: Parallax Propeller Walter Banks <walter@bytecraft.com> - 2013-01-20 17:12 -0500
                Re: Parallax Propeller Mel Wilson <mwilson@the-wire.com> - 2013-01-20 19:19 -0500
                Re: Parallax Propeller Walter Banks <walter@bytecraft.com> - 2013-01-20 21:12 -0500
                Re: Parallax Propeller David Brown <david@westcontrol.removethisbit.com> - 2013-01-21 09:01 +0100
                Re: Parallax Propeller Walter Banks <walter@bytecraft.com> - 2013-01-21 21:11 -0500
                Re: Parallax Propeller upsidedown@downunder.com - 2013-01-22 09:39 +0200
                Re: Parallax Propeller Mel Wilson <mwilson@the-wire.com> - 2013-01-22 10:14 -0500
              Re: Parallax Propeller Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2013-01-20 02:03 +0000
            Re: Parallax Propeller George Neuner <gneuner2@comcast.net> - 2013-01-19 12:29 -0500
              Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-23 12:29 -0500
                Re: Parallax Propeller Mark Wills <markrobertwills@yahoo.co.uk> - 2013-01-24 14:03 -0800
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-01-24 22:55 -0800
                Re: Parallax Propeller Mark Wills <forthfreak@gmail.com> - 2013-01-24 23:03 -0800
                Re: Parallax Propeller Coos Haak <chforth@hccnet.nl> - 2013-01-25 20:02 +0100
                Re: Parallax Propeller Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-01-28 17:13 -0800
                Re: Parallax Propeller David Brown <david@westcontrol.removethisbit.com> - 2013-01-29 09:15 +0100
                Re: Parallax Propeller Anders.Montonen@kapsi.spam.stop.fi.invalid - 2013-01-30 12:19 +0000
                Re: Parallax Propeller David Brown <david.brown@removethis.hesbynett.no> - 2013-01-30 21:18 +0100
                Re: Parallax Propeller Mark Wills <forthfreak@gmail.com> - 2013-01-30 22:57 -0800
                Re: Parallax Propeller Alex McDonald <blog@rivadpm.com> - 2013-01-31 10:38 -0800
                Re: Parallax Propeller Mark Wills <forthfreak@gmail.com> - 2013-01-31 12:34 -0800
            Re: Parallax Propeller Paul Rubin <no.email@nospam.invalid> - 2013-01-19 10:42 -0800
              Re: Parallax Propeller bob@bob.com - 2013-01-19 19:56 -0600
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-23 12:40 -0500
                Re: Parallax Propeller None <vandys@vsta.org> - 2013-01-24 23:26 +0000
                Re: Parallax Propeller Walter Banks <walter@bytecraft.com> - 2013-01-25 11:49 -0500
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-25 09:25 -0500
                Re: Parallax Propeller None <vandys@vsta.org> - 2013-01-25 21:57 +0000
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-26 18:07 -0500
                Re: Parallax Propeller Mark Wills <markrobertwills@yahoo.co.uk> - 2013-01-27 00:50 -0800
                Re: Parallax Propeller Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-27 03:30 -0600
                Re: Parallax Propeller Dombo <dombo@disposable.invalid> - 2013-01-27 12:58 +0100
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-28 21:38 -0500
                Re: Parallax Propeller None <vandys@vsta.org> - 2013-01-27 03:09 +0000
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-28 21:51 -0500
                Re: Parallax Propeller None <vandys@vsta.org> - 2013-01-30 02:10 +0000
                Re: Parallax Propeller rickman <gnuarm@gmail.com> - 2013-01-30 18:32 -0500
            Re: Parallax Propeller David Schultz <abuse@127.0.0.1> - 2013-01-20 11:21 -0600
      Re: Parallax Propeller albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-01-13 16:24 +0000
      Re: Parallax Propeller David Brown <david@westcontrol.removethisbit.com> - 2013-01-14 10:51 +0100
        Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 06:06 +0000
          Re: Parallax Propeller David Brown <david@westcontrol.removethisbit.com> - 2013-01-16 13:43 +0100
            Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 15:27 +0000
      Re: Parallax Propeller Rafael Deliano <rafael_deliano@arcor.de> - 2013-01-15 21:10 +0100
        Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-16 06:26 +0000
      Re: Parallax Propeller gavino_himself <visploveslisp@gmail.com> - 2013-01-22 06:26 -0800
    Re: Parallax Propeller Peter Jakacki <peterjakacki@gmail.com> - 2013-01-13 12:44 +0000

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