From: Lars-Peter Clausen <firstname.lastname@example.org> To: Gregor Boirie <email@example.com>, Jonathan Cameron <firstname.lastname@example.org>, Jonathan Cameron <email@example.com>, firstname.lastname@example.org Subject: Re: using monotonic clok for timstamping Date: Tue, 9 Feb 2016 21:52:06 +0100 [thread overview] Message-ID: <56BA5176.email@example.com> (raw) In-Reply-To: <56B9C826.firstname.lastname@example.org> 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.
next prev 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
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