Re: Getting started with AVR and C

From	John Devereux <john@devereux.me.uk>
Newsgroups	comp.arch.embedded, comp.lang.c
Subject	Re: Getting started with AVR and C
Date	2012-11-30 08:29 +0000
Message-ID	<87hao7h4t2.fsf@devereux.me.uk> (permalink)
References	(7 earlier) <JaGdnWKCkdElJyvNnZ2dnUVZ_oOXnZ2d@web-ster.com> <k97v17$jpg$4@reader1.panix.com> <87boegicx9.fsf@devereux.me.uk> <v8hfb8p4eppqeqe52rr3ngemub6jcsd1ao@4ax.com> <k98lsr$60d$1@reader1.panix.com>

Cross-posted to 2 groups.

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Grant Edwards <invalid@invalid.invalid> writes:

> On 2012-11-29, upsidedown@downunder.com <upsidedown@downunder.com> wrote:
>> On Thu, 29 Nov 2012 16:36:34 +0000, John Devereux
>><john@devereux.me.uk> wrote:
>>
>>>Grant Edwards <invalid@invalid.invalid> writes:
>>>
>>>> On 2012-11-29, Tim Wescott <tim@seemywebsite.com> wrote:
>>>>
>>>>> It's certainly what I would expect from gcc-avr.  There's no reason you 
>>>>> can't make a beautifully compliant, reasonably efficient compiler that 
>>>>> works well on the AVR.
>>>>
>>>> avr-gcc does indeed work very nicely as long as you don't look at the
>>>> code generated when you use pointers.  You'll go blind -- especially
>>>> if you're used to something like the msp430.  It's easy to forget that
>>>> the AVR is an 8-bit CPU not a 16-bit CPU like the '430, and use of
>>>> 16-bit pointers on the AVR requires a lot of overhead.
>>>
>>>Other problem with it is the separate program and data memory
>>>spaces. Fine for small deeply embedded things but started to show strain
>>>when I wanted a LCD display, menus etc. I would not use it for a new
>>>project unless there was a very good reason, ultra-low power
>>>perhaps. Cortex M3 is much nicer but the chips are much more complicated
>>>of course.
>>
>> Except for self modifying code, why would one want data (program)
>> access into program space (unless you are writing a linker or
>> debugger) ??
>
> The "program" space was flash (non-volatile).  The "data" space was
> registers and RAM (volatile).  All non-volatile data (strings, screen
> templates, lookup tables, menu structures, and so) has to be in flash
> memory (IOW "program space").  It makes a _lot_ of sense to just use
> directly from flash instead of copying it all to RAM when RAM is so
> scarce.

Yes, that is precisely it. The AVRs especially tended to have lots of
flash but little RAM. Access to program memory is possible on the AVR,
but you have to use special attribute modifiers everywhere and the
resulting objects become incompatible with the standard libraries, so
you have to write special versions of these...

Another thing is that, being an 8 bit machine, int and short operations
are not atomic. So you have to be very careful about protecting
variables shared with interrupt handlers (or other tasks in a preemptive
system). Good practice anyway of course but a modern CPU like Cortex M3
is a lot more forgiving since even 32 bit load/store operations are
atomic.

[...]


-- 

John Devereux

Thread

Getting started with AVR and C Robert Roland <fake@ddress.no> - 2012-11-24 17:41 +0100
  Re: Getting started with AVR and C hamilton <hamilton@nothere.com> - 2012-11-24 09:55 -0700
    Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 10:39 +0100
  Re: Getting started with AVR and C Rene <a@b.c> - 2012-11-24 18:03 +0100
    Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-10 13:21 +0100
      Re: Getting started with AVR and C Christopher Head <chead@is.invalid> - 2012-12-10 18:33 -0800
        Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-11 12:34 +0100
  Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-24 12:44 -0600
  Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:12 -0800
  Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-24 11:28 -0800
    Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:42 -0800
      Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-25 07:01 -0800
    Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 20:14 +0100
  Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 03:18 +0700
  Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 04:18 +0700
    Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-11-24 17:09 -0500
    Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-24 22:12 +0000
      Re: Getting started with AVR and C Dave Nadler <drn@nadler.com> - 2012-11-24 21:01 -0800
        statement / expression contexts in C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 12:54 +0700
      Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 13:37 +0700
        Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-28 14:49 +0000
        Re: Getting started with AVR and C Frank Miles <fpm@u.washington.edu> - 2012-11-28 17:53 +0000
          Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 18:05 +0000
            Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 12:56 -0600
              Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-28 21:45 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 15:55 -0600
                Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-29 01:35 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 01:47 +0100
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:24 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 01:18 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 20:07 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:23 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 11:01 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 19:19 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 14:32 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 11:44 -0800
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 21:23 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:15 -0800
                Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-30 09:26 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 13:22 -0800
                Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-30 14:10 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:16 -0800
                Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-11-30 17:36 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:18 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 10:08 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 00:45 -0800
                Re: Getting started with AVR and C Ed Beroset <beroset@mindspring.com> - 2012-12-01 08:00 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 13:22 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-01 17:33 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 17:43 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-02 14:13 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-04 20:34 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-04 18:25 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 07:55 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:11 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-05 07:52 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 11:02 -0500
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 21:28 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:21 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:05 +0200
                Re: Getting started with AVR and C Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2012-12-05 23:22 +0200
                Re: Getting started with AVR and C Niklas Holsti <niklas.holsti@tidorum.invalid> - 2012-12-06 00:00 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:17 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:10 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-06 07:15 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 21:52 -0800
                Re: Getting started with AVR and C Lanarcam <lanarcam1@yahoo.fr> - 2012-12-06 20:59 +0100
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-06 12:38 -0800
                Re: Getting started with AVR and C George Neuner <gneuner2@comcast.net> - 2012-12-06 20:39 -0500
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 22:31 -0500
                Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-12-05 16:32 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-05 17:04 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 22:01 -0800
                Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-12-06 14:05 +0000
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-06 10:28 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 16:58 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 07:34 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 10:55 -0500
                Re: Getting started with AVR and C Rich Webb <bbew.ar@mapson.nozirev.ten> - 2012-12-06 11:11 -0500
                Re: Getting started with AVR and C Rocky <RobertGush@gmail.com> - 2012-12-06 21:38 -0800
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-07 03:49 -0800
                Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 02:58 -0600
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 17:28 +0200
                Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 11:55 -0600
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:17 +0200
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 12:36 -0800
                Re: Getting started with AVR and C Stephen Sprunk <stephen@sprunk.org> - 2012-11-29 16:22 -0600
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:36 -0800
                Re: Getting started with AVR and C "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2012-12-11 10:53 +0100
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-11 14:53 +0000
                Unicode Ivan Shmakov <oneingray@gmail.com> - 2012-12-14 23:25 +0700
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 14:30 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 12:24 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 18:02 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 15:45 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-16 22:55 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-16 23:20 -0800
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:27 +0200
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-17 11:17 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:07 +0000
                Re: Getting started with AVR and C Nobody <nobody@nowhere.com> - 2012-12-16 03:28 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-16 10:40 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 02:31 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 03:36 +0000
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 03:55 +0000
                Re: Getting started with AVR and C Christopher Head <chead@is.invalid> - 2012-11-28 23:24 -0800
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:37 +0100
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:31 +0000
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 13:44 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 13:22 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:32 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:28 -0800
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:20 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:07 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:17 -0500
                Re: Getting started with AVR and C pete <pfiland@mindspring.com> - 2012-11-29 18:25 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 22:46 -0500
                Re: Getting started with AVR and C lawrence.jones@siemens.com - 2012-11-30 11:47 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:38 -0800
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 15:21 -0500
              Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 22:26 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 17:32 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 19:02 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 18:29 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:39 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-29 00:59 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 07:57 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-29 13:02 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:19 +0000
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-11-29 12:03 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:39 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 08:04 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:17 +0000
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:19 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:44 -0500
          Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 13:15 -0500
            Re: Getting started with AVR and C Arlet Ottens <usenet+5@c-scape.nl> - 2012-11-28 19:17 +0100
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:30 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:29 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-29 16:36 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:40 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 13:55 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 22:06 +0000
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 14:22 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 21:59 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-30 08:29 +0000
    Re: Getting started with AVR and C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:41 -0800
    Re: Getting started with AVR and C Rosario1903 <Rosario@invalid.invalid> - 2012-11-27 10:21 +0100
  Re: Getting started with AVR and C dbr@kbrx.com - 2012-11-24 21:49 +0000
    Re: Getting started with AVR and C MK <mk@nospam.co.uk> - 2012-11-25 12:24 +0000
      Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-11-26 00:08 +0000

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