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Re: 7 lessons for embedded developers from ESC Boston 2015

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On 6/5/15 4:55 AM, Raimond Dragomir wrote:
> vineri, 5 iunie 2015, 13:48:15 UTC+3, Stephen Pelc a scris:
>> On Fri, 05 Jun 2015 03:15:54 -0400, rickman <gnuarm@gmail.com> wrote:
>>
>>> I don't know this is strictly true.  I believe there are some forths out
>>> there that incorporate an RTOS or at least multitasking/multiuser and
>>> not necessarily cooperative.  I don't recall any names, but I recall
>>> this being discussed.
>>
>> What stops a cooperative scheduler from being (hard) real time?
>>
> It's just crazy even to try to reach hard real time requirements with
> a cooperative rtos. Even a 10Hz task (100ms sharp, or ok take it with
> a +100us jitter). Unless your system has almost nothing to do and waits
> for the 100ms to schedule the "hard" real time task...

Certainly you need interrupts to do hard real-time. But there's no 
inconsistency between having a simple cooperative scheduler and 
interrupts not only from a clock but also the devices you're controlling.

>> Im my experience, two things. Program bugs and assumptions leading
>> to program bugs. In both cases, a simple cooperative scheduler with
>> a timeout interrupt is good enough.
>>
> Good enough is another thing. The interrupt can meet the hard real time
> requirement. I'm using such systems for almost twenty years. Hard realtime
> only with interrupts. Anything else is soft real-time with cooperative
> tasks.

The rule in FORTH, Inc. multitaskers is that a task that initiates I/O 
then sleeps until the I/O is complete. Whether completion is signaled by 
an interrupt or polling (1 or 2 instructions per poll, and the task is 
back to sleep again, so not very intrusive), that means in practice most 
tasks are asleep most of the time. In the rare case where there is some 
very intensive CPU-intensive activity (e.g. a big sort of stuff all in 
memory) it's very easy to insert a PAUSE in convenient spots in the process.

>> Since bare-metal Forths do not have buried code, the distinction
>> between tools such as the multitasker and the application code
>> is only one of name, not of availability. Whether these tools
>> form an RTOS or not is simply a question of whether there is a
>> consistent and documented API over a range of processors and/or
>> implementations.
>>
>> Stephen

Agreed.

Cheers,
Elizabeth

-- 
==================================================
Elizabeth D. Rather   (US & Canada)   800-55-FORTH
FORTH Inc.                         +1 310.999.6784
5959 West Century Blvd. Suite 700
Los Angeles, CA 90045
http://www.forth.com

"Forth-based products and Services for real-time
applications since 1973."
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7 lessons for embedded developers from ESC Boston 2015 visualforth@rocketmail.com - 2015-05-19 15:44 -0700
  Re: 7 lessons for embedded developers from ESC Boston 2015 "Elizabeth D. Rather" <erather@forth.com> - 2015-05-19 14:55 -1000
    Re: 7 lessons for embedded developers from ESC Boston 2015 visualforth@rocketmail.com - 2015-05-20 10:04 -0700
  Re: 7 lessons for embedded developers from ESC Boston 2015 Mark Wills <markwills1970@gmail.com> - 2015-05-20 00:29 -0700
    Re: 7 lessons for embedded developers from ESC Boston 2015 djc <ciesinger@gmx.net> - 2015-05-20 03:47 -0700
    Re: 7 lessons for embedded developers from ESC Boston 2015 hughaguilar96@gmail.com - 2015-06-04 21:02 -0700
      Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-04 23:31 -0700
        Re: 7 lessons for embedded developers from ESC Boston 2015 rickman <gnuarm@gmail.com> - 2015-06-05 03:15 -0400
          Re: 7 lessons for embedded developers from ESC Boston 2015 stephen@mpeforth.com (Stephen Pelc) - 2015-06-05 10:48 +0000
            Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-05 07:55 -0700
              Re: 7 lessons for embedded developers from ESC Boston 2015 stephen@mpeforth.com (Stephen Pelc) - 2015-06-05 15:54 +0000
                Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-05 09:32 -0700
                Re: 7 lessons for embedded developers from ESC Boston 2015 "Elizabeth D. Rather" <erather@forth.com> - 2015-06-05 07:46 -1000
                Re: 7 lessons for embedded developers from ESC Boston 2015 hughaguilar96@gmail.com - 2015-06-06 16:28 -0700
                Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-06 21:00 -0700
                Re: 7 lessons for embedded developers from ESC Boston 2015 visualforth@rocketmail.com - 2015-06-09 10:04 -0700
                Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-09 10:58 -0700
                Re: 7 lessons for embedded developers from ESC Boston 2015 Paul Rubin <no.email@nospam.invalid> - 2015-06-07 20:40 -0700
              Re: 7 lessons for embedded developers from ESC Boston 2015 "Elizabeth D. Rather" <erather@forth.com> - 2015-06-05 07:40 -1000
          Re: 7 lessons for embedded developers from ESC Boston 2015 "Elizabeth D. Rather" <erather@forth.com> - 2015-06-05 07:31 -1000
        Re: 7 lessons for embedded developers from ESC Boston 2015 Mark Wills <markwills1970@gmail.com> - 2015-06-05 05:35 -0700
          Re: 7 lessons for embedded developers from ESC Boston 2015 foxaudioresearch@gmail.com - 2015-06-05 06:05 -0700
            Re: 7 lessons for embedded developers from ESC Boston 2015 Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-06-05 07:43 -0700
              Re: 7 lessons for embedded developers from ESC Boston 2015 rickman <gnuarm@gmail.com> - 2015-06-05 14:47 -0400
              Re: 7 lessons for embedded developers from ESC Boston 2015 albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-06-06 09:28 +0000
            Re: 7 lessons for embedded developers from ESC Boston 2015 Mark Wills <markwills1970@gmail.com> - 2015-06-05 10:43 -0700
              Re: 7 lessons for embedded developers from ESC Boston 2015 Paul Rubin <no.email@nospam.invalid> - 2015-06-07 20:03 -0700

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