Re: $0.03 microcontroller

From	Philipp Klaus Krause <pkk@spth.de>
Newsgroups	comp.arch.embedded
Subject	Re: $0.03 microcontroller
Date	2018-11-08 21:56 +0100
Organization	solani.org
Message-ID	<ps27tg$2t6$1@solani.org> (permalink)
References	<nfcvD.142609$MN2.62078@fx02.iad> <pppldh$thf$1@solani.org> <66q1sd9b3vvic0jfc14ei1g1ua97iqpksj@4ax.com> <ps1bks$eaj$1@solani.org> <gr29udt5koa6bu0t5vu9bu8qntsktah8ns@4ax.com>

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Am 08.11.18 um 20:52 schrieb upsidedown@downunder.com:
>>
>> But static memory allocation would require one copy of each function per
>> thread. 
> 
> For a foreground/background monitor, the worst case would be two
> copies of static data, if both threads use the same rubroutine.
> 
>> And the linker would have to analyze the call graph to always
>> call the correct function for each thread. 
> 
> Linker for such small target ?

Of course. The support routines the compiler uses reside in some
library, the linker links them in if necessary. Also, the larger
variants are not that small, with up to 256 B of RAM and 8 KB of ROM.
One might want to e.g. have one .c file for handling I²", one for the
soft UART, etc.

> 
> With such small processor, just track any dependencies manually.

See above.

> 
>> Function pointers get complicated.
> 
> Do you really insist of using function pointer with such small
> targets?
> 

I want to have C, function pointers are part of it.

>>
>> Unfortunately, reentrancy becomes even harder with
>> hardware-multithreading: 
> 
> With two hardware threads, you would need at most two copies of static
> data.

Padauk still makes one chip with 8 hardware threads (and it looks to me
as if there were more in the past, though they are not currently listed
on their website, one can find them e.g. in their IDE).

> 
>> TO access the stack, one has to construct a
>> pointer to the stack location in a memory location. 
> 
> Why would you want to access the stack ?

For reentrency, so I can use one function implementation for all
threads. It would also be useful to dynamically assign threads to
hardware threads (so no thread is tied to specific hardware, and some OS
schedules them).

> 
> The stack is usable for handling return addresses, but I guess that a
> hardware thread must have its own return address stack  pointer.

Each hardware thread has its flag register (4 bits) accumulator (8
bits), pc (12 bits) and stack pointer (8 bits).

> 
>> That memory location
>> (as any pseudo-registers) is then shared among all running instances of
>> the function. So it needs to be protected (e.g. with a spinlock), making
>> access even more inefficient. And that spinlock will cause issues with
>> interrupts (a solution might be to heavily restrict interrupt routines,
>> essentially allowing not much more than setting some global variables).
> 
> Disabling all interrupts for the duration of some critical operations
> is often enough, but of course, the number of instructions executed
> during interrupt disabled should be minimized.

Disabling interrupts any time a spinlock is held or a thread is wating
for one might be too much, especially if there are many threads, so the
spinlock is held often.

Philipp

Thread

$0.03 microcontroller Clifford Heath <no.spam@please.net> - 2018-10-10 12:05 +1100
  Re: $0.03 microcontroller lasselangwadtchristensen@gmail.com - 2018-10-10 16:12 -0700
  Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-10 17:51 -0700
    Re: $0.03 microcontroller lasselangwadtchristensen@gmail.com - 2018-10-10 18:56 -0700
  Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-10 19:29 -0700
    Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-11 11:39 +0300
      Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-11 16:08 -0700
        Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-12 08:50 +0200
          Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-12 09:44 +0200
            Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-12 21:30 +0300
              Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-12 22:06 +0200
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-12 23:45 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-13 21:47 +0200
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-14 11:58 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-15 08:14 +0200
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-11 09:27 +0100
                Re: $0.03 microcontroller Klaus Kragelund <klauskvik@hotmail.com> - 2018-12-26 02:23 -0800
              Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-15 10:44 +0200
                Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-15 07:29 -0700
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-16 09:19 +0200
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-16 13:48 +0200
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-15 21:34 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-16 09:29 +0200
                Re: $0.03 microcontroller Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2018-10-15 21:22 +0200
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-16 10:00 +0200
                Re: $0.03 microcontroller Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2018-10-16 22:52 +0200
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-16 14:01 -0700
                Re: $0.03 microcontroller Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2018-10-17 00:03 +0200
                Re: $0.03 microcontroller Clifford Heath <no.spam@please.net> - 2018-10-17 09:22 +1100
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-16 15:29 -0700
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-17 00:46 +0200
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-17 09:35 +0300
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-17 09:31 +0200
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-17 07:08 -0700
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-17 18:37 +0300
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-17 10:04 -0700
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-17 23:07 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-17 08:23 +0200
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-17 19:43 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-17 20:24 +0200
                Re: $0.03 microcontroller George Neuner <gneuner2@comcast.net> - 2018-10-17 11:31 -0400
            Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-05 12:41 +0100
          Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-12 09:11 -0700
            Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-13 12:46 +0200
              Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-13 05:06 -0700
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-13 18:00 +0300
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-13 18:27 +0200
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-13 20:50 +0300
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-14 14:26 +0200
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-13 18:20 -0700
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-14 08:53 +0200
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-14 08:55 +0200
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-14 14:32 +0200
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-13 18:21 +0200
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-13 18:32 -0700
                Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-13 19:02 -0700
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-14 14:37 +0200
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-14 14:59 +0200
                Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-13 11:06 -0700
            Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-13 18:31 +0300
              Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-13 19:46 +0300
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-13 19:59 +0300
                Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-13 21:31 +0300
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-13 22:19 +0300
                Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-13 21:24 +0200
                Re: $0.03 microcontroller Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-10-13 22:50 +0300
                Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-14 14:39 +0200
                Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-15 05:11 -0700
              Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-13 21:03 +0300
              Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-13 18:25 -0700
          Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-15 14:20 +0200
    Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-21 16:27 +0300
      Re: $0.03 microcontroller jim.brakefield@ieee.org - 2018-10-21 07:47 -0700
        Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-21 08:08 -0700
          Re: $0.03 microcontroller jim.brakefield@ieee.org - 2018-10-21 09:31 -0700
            Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-21 10:51 -0700
              Re: $0.03 microcontroller jim.brakefield@ieee.org - 2018-10-21 12:44 -0700
                Re: $0.03 microcontroller Brett <ggtgp@yahoo.com> - 2018-10-22 00:28 +0000
          Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-21 21:43 +0200
      Re: $0.03 microcontroller Phil Martel <pomartel@comcast.net> - 2018-10-21 11:03 -0400
      Re: $0.03 microcontroller George Neuner <gneuner2@comcast.net> - 2018-10-21 20:59 -0400
  Re: $0.03 microcontroller Michael Kellett <mk@mkesc.co.uk> - 2018-10-11 14:04 +0100
    Re: $0.03 microcontroller David Brown <david.brown@hesbynett.no> - 2018-10-11 15:56 +0200
      Re: $0.03 microcontroller Michael Kellett <mk@mkesc.co.uk> - 2018-10-13 09:35 +0100
        Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-13 13:06 -0700
          Re: $0.03 microcontroller Michael Kellett <mk@mkesc.co.uk> - 2018-10-14 11:30 +0100
  Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-12 10:18 +0200
    Re: $0.03 microcontroller upsidedown@downunder.com - 2018-10-12 21:39 +0300
      Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-08 13:53 +0100
        Re: $0.03 microcontroller Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-11-08 15:08 +0200
          Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-08 14:34 +0100
        Re: $0.03 microcontroller upsidedown@downunder.com - 2018-11-08 21:52 +0200
          Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-08 21:56 +0100
            Re: $0.03 microcontroller upsidedown@downunder.com - 2018-11-09 00:35 +0200
              Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-11-09 09:00 +0100
    Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-15 14:19 +0200
  Re: $0.03 microcontroller Tim <cpldcpu+usenet@gmail.com> - 2018-10-14 01:46 +0200
    Re: $0.03 microcontroller Theo <theom+news@chiark.greenend.org.uk> - 2018-10-14 10:55 +0100
      Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-24 15:57 +0200
  Re: $0.03 microcontroller Philipp Klaus Krause <pkk@spth.de> - 2018-10-15 14:35 +0200
    Re: $0.03 microcontroller raimond.dragomir@gmail.com - 2018-10-15 06:05 -0700
      Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-15 07:19 -0700
        Re: $0.03 microcontroller Paul Rubin <no.email@nospam.invalid> - 2018-10-15 07:26 -0700
          Re: $0.03 microcontroller gnuarm.deletethisbit@gmail.com - 2018-10-15 07:30 -0700

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