All of lore.kernel.org
 help / color / mirror / Atom feed
From: Lars-Peter Clausen <lars@metafoo.de>
To: Gregor Boirie <gregor.boirie@parrot.com>,
	Jonathan Cameron <jic23@jic23.retrosnub.co.uk>,
	Jonathan Cameron <jic23@kernel.org>,
	linux-iio@vger.kernel.org
Subject: Re: using monotonic clok for timstamping
Date: Tue, 9 Feb 2016 21:52:06 +0100	[thread overview]
Message-ID: <56BA5176.6020108@metafoo.de> (raw)
In-Reply-To: <56B9C826.1090309@parrot.com>

On 02/09/2016 12:06 PM, Gregor Boirie wrote:
> To sump up, implementing timestamping clock selection support in IIO
> should be based on the following principles.
> 
> Selected timestamping clock is a per-device attribute which the userspace
> may access through a sysfs file.
> 
> It must be applicable to both buffered samples and events.

Just playing out ideas here to make sure we have everything covered, but
could be there be a setup where you'd want different timestamps for events
and buffers?

> 
> Userspace may choose amongst a subset of available POSIX clocks. A good
> starting point would be: CLOCK_REALTIME, CLOCK_MONOTONIC,
> CLOCK_MONOTONIC_RAW, CLOCK_REALTIME_COARSE,
> CLOCK_MONOTONIC_COARSE, CLOCK_BOOTTIME and CLOCK_TAI.
> Please delete as appropriate if needed and see clock_gettime(2).
> 
> One remaining question is : how do we ensure sample and event timestamps
> consistency with respect to clock changes ? 2 suggestions:
> * reject the ability to select a new clock as long as an events chardev is
> opened
>   or a buffered samples channel is enabled ;
> * clock may be changed at any time since it could be implemented in an atomic
>   way (a simple atomic_t can hold an int / clockid_t if I'm no wrong).

Not sure if we need to prevent it. If somebody changes it during an active
measurement it is their problem I'd say.


  parent reply	other threads:[~2016-02-09 20:52 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-03 10:55 Gregor Boirie
2016-02-03 11:22 ` Lars-Peter Clausen
2016-02-06 18:33   ` Jonathan Cameron
2016-02-08  9:55     ` Lars-Peter Clausen
2016-02-08 17:15       ` Jonathan Cameron
2016-02-09 11:06         ` Gregor Boirie
2016-02-09 14:19           ` Gregor Boirie
2016-02-09 20:49             ` Jonathan Cameron
2016-02-09 20:52           ` Lars-Peter Clausen [this message]
2016-02-09 21:02             ` Jonathan Cameron
2016-02-10  9:46             ` Gregor Boirie

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=56BA5176.6020108@metafoo.de \
    --to=lars@metafoo.de \
    --cc=gregor.boirie@parrot.com \
    --cc=jic23@jic23.retrosnub.co.uk \
    --cc=jic23@kernel.org \
    --cc=linux-iio@vger.kernel.org \
    --subject='Re: using monotonic clok for timstamping' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.