Re: $0.03 microcontroller

From	Philipp Klaus Krause <pkk@spth.de>
Newsgroups	comp.arch.embedded
Subject	Re: $0.03 microcontroller
Date	2018-11-08 13:53 +0100
Organization	solani.org
Message-ID	<ps1bks$eaj$1@solani.org> (permalink)
References	<nfcvD.142609$MN2.62078@fx02.iad> <pppldh$thf$1@solani.org> <66q1sd9b3vvic0jfc14ei1g1ua97iqpksj@4ax.com>

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Am 12.10.18 um 20:39 schrieb upsidedown@downunder.com:
> On Fri, 12 Oct 2018 10:18:56 +0200, Philipp Klaus Krause <pkk@spth.de>
> wrote:
> 
>> Am 10.10.2018 um 03:05 schrieb Clifford Heath:
>>> <https://lcsc.com/product-detail/PADAUK_PADAUK-Tech-PMS150C_C129127.html>
>>> <http://www.padauk.com.tw/upload/doc/PMS150C%20datasheet%20V004_EN_20180124.pdf>
>>>
>>>
>>> OTP, no SPI, UART or I²C, but still...
>>>
>>> Clifford Heath
>>
>> They even make dual-core variants (the part where the first digit in the
>> part number is '2'). It seems program counter, stack pointer, flag
>> register and accumulator are per-core, while the rest, including the ALU
>> is shared. In particular, the I/O registers are also shared, which means
>> some multiplier registers would also be - but currently all variants
>> with integrated multiplier are single-core.
>> Use of the ALU is shared byt he two cores, alternating by clock cycle.
>>
>> Philipp
> 
> 
> Interesting, that would make it easy to run a multitasking RTOS
> (foreground/background) monitor, which might justify the use of some
> reentrant library routines :-). But in reality, the available memory
> (ROM/RAM) is so small so that you could easily manage this with static
> memory allocations.
> 
> 

But static memory allocation would require one copy of each function per
thread. And the linker would have to analyze the call graph to always
call the correct function for each thread. Function pointers get
complicated.

Unfortunately, reentrancy becomes even harder with
hardware-multithreading: TO access the stack, one has to construct a
pointer to the stack location in a memory location. 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).

The there is the trade-off of using one such memory location per
function vs. per program (the latter reducing memroy usage, but
resulting in less paralellism).

The pseudo-registers one would want to use are not so much a problem for
interrupt routines (they would just need saving and thus increase
interrupt overhead a bit), but for hardware parallelism. Essentially all
access to them would again have to be protected by a spinlock.

All these problems could have relatively easily been avoided by
providing an efficient stack-pointer-relative addressing mode. Having a
few general-purpose or index registers would have somewhat helped as well.

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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