Re: Delayed "printf"

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.arch.embedded
Subject	Re: Delayed "printf"
Date	2017-04-25 10:58 +0200
Organization	A noiseless patient Spider
Message-ID	<odn2t2$f4m$1@dont-email.me> (permalink)
References	<R6WdnUr9KJ3rBmPFnZ2dnUU7-K2dnZ2d@giganews.com>

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On 25/04/17 02:42, Tim Wescott wrote:
> Sometimes it's necessary to float a notion just so that someone can 
> affirm your suspicion that yes, you really are an idiot.
> 
> On the off chance that I'm a genius, though, here goes:
> 
> I don't like putting "printf" in fast tasks for obvious reasons -- even 
> with infinite spooling, it can take time to process a format string.  In 
> my usual context, this can result in audible sounds from motors when I 
> print some bit of debugging information from a high-priority task.  The 
> problem can't be alleviated by spooling the output of the printf, because 
> it's the execution time of the printf itself that's the problem.
> 
> Just how dumb is it to have "printf" queue up the format string AND the 
> parameters into a buffer, to be printed out in some low-priority task?  
> For a system with sufficient memory, this seems like an astonishingly 
> sensible thing to me.
> 
> Clearly you'd have to wrap it up somehow so that if the buffer was full 
> no printf at all would happen -- but I'm kinda liking the notion.
> 
> So -- whatcha think?
> 

printf is a horrible function for such purposes - with its variable
arguments, etc.  Consider having delayed_print_string(),
delayed_print_int(), delayed_print_hex(), etc., so that you can have a
queue with of structs with a fixed format (a tag for the type to be
printed, a union of the data types, etc.).  It is a lot easier to keep
control of a fixed set of types of a specific number, than a general
variable argument set.

If you have a C11 compiler and can grok _Generic, you can wrap the whole
thing in variable argument macros and get a programming interface such as:

delayed_print("Current pos: ", position, " register: 0x", hex(reg, 4),
endline);

But if you do go for a printf-style function, don't forget gcc's
"format" __attribute__ on your function to check that the formatting and
the arguments match up - it will save much wailing and gnashing of teeth.

Thread

Delayed "printf" Tim Wescott <seemywebsite@myfooter.really> - 2017-04-24 19:42 -0500
  Re: Delayed "printf" Don Y <blockedofcourse@foo.invalid> - 2017-04-24 18:51 -0700
    Re: Delayed "printf" Tim Wescott <tim@seemywebsite.com> - 2017-04-24 21:54 -0500
      Re: Delayed "printf" Don Y <blockedofcourse@foo.invalid> - 2017-04-24 21:27 -0700
  Re: Delayed "printf" Paul Rubin <no.email@nospam.invalid> - 2017-04-24 19:53 -0700
  Re: Delayed "printf" Clifford Heath <no.spam@please.net> - 2017-04-25 13:01 +1000
    Re: Delayed "printf" Theo Markettos <theom+news@chiark.greenend.org.uk> - 2017-04-25 18:51 +0100
      Re: Delayed "printf" Clifford Heath <no.spam@please.net> - 2017-04-26 12:59 +1000
        Re: Delayed "printf" Theo Markettos <theom+news@chiark.greenend.org.uk> - 2017-04-26 13:24 +0100
  Re: Delayed "printf" Robert Wessel <robertwessel2@yahoo.com> - 2017-04-25 00:19 -0500
    Re: Delayed "printf" David Brown <david.brown@hesbynett.no> - 2017-04-25 10:44 +0200
      Re: Delayed "printf" Robert Wessel <robertwessel2@yahoo.com> - 2017-04-25 09:22 -0500
        Re: Delayed "printf" David Brown <david.brown@hesbynett.no> - 2017-04-25 16:37 +0200
    Re: Delayed "printf" Tim Wescott <tim@seemywebsite.com> - 2017-04-25 10:49 -0500
  Re: Delayed "printf" Jack <jack4747@gmail.com> - 2017-04-24 23:33 -0700
  Re: Delayed "printf" Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-04-25 08:09 +0100
  Re: Delayed "printf" John Devereux <john@devereux.me.uk> - 2017-04-25 08:14 +0100
  Re: Delayed "printf" David Brown <david.brown@hesbynett.no> - 2017-04-25 10:58 +0200
  Re: Delayed "printf" Stefan Reuther <stefan.news@arcor.de> - 2017-04-25 18:46 +0200
  Re: Delayed "printf" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-04-25 21:03 +0200
  Re: Delayed "printf" Tim Wescott <seemywebsite@myfooter.really> - 2017-04-25 16:11 -0500
    Re: Delayed "printf" Les Cargill <lcargill99@comcast.com> - 2017-04-25 17:28 -0500
    Re: Delayed "printf" Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-04-26 10:03 +0300
  Re: Delayed "printf" Dave Nadler <drn@nadler.com> - 2017-04-25 14:31 -0700
  Re: Delayed "printf" Les Cargill <lcargill99@comcast.com> - 2017-04-25 17:25 -0500
  Re: Delayed "printf" mac <acolvin@efunct.com> - 2017-04-26 17:22 +0000
    Re: Delayed "printf" Grant Edwards <invalid@invalid.invalid> - 2017-04-26 17:37 +0000
      Re: Delayed "printf" Grant Edwards <invalid@invalid.invalid> - 2017-04-26 17:38 +0000

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