Date: Fri, 4 Oct 2019 16:05:20 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: Poul-Henning Kamp <phk@phk.freebsd.dk>, Warner Losh <imp@bsdimp.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, Bruce Evans <brde@optusnet.com.au>, FreeBSD <freebsd-hackers@freebsd.org> Subject: Re: Why is tc_get_timecount() called two times in tc_init()? Message-ID: <141ee0af-2ff4-50fc-b4e4-6d1fc47e04f3@embedded-brains.de> In-Reply-To: <47834.1570116246@critter.freebsd.dk> References: <0e27fb3e-0f60-68e1-dbba-f17c3d91c332@embedded-brains.de> <20191002140040.GA44691@kib.kiev.ua> <20191003013314.O2151@besplex.bde.org> <20191002163946.GE44691@kib.kiev.ua> <20191003030837.C2787@besplex.bde.org> <20191003084021.GI44691@kib.kiev.ua> <CANCZdfpcOBJiYAKafhiWZS2g4vnLGVvzqhaOXetSSnU2Hj91nw@mail.gmail.com> <47834.1570116246@critter.freebsd.dk>
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On 03/10/2019 17:24, Poul-Henning Kamp wrote: > -------- > In message <CANCZdfpcOBJiYAKafhiWZS2g4vnLGVvzqhaOXetSSnU2Hj91nw@mail.gmail.com> > , Warner Losh writes: > >> I think this is a good fix. I recall phk saying it was more paranoia for >> edge cases than really needed in a private email to me, but it's in the >> 'gap' of email that I lost in a disk crash 12 years ago so I can't find it >> for sure. > > I think the original reason for this was (locked) delta-based > timecounters, (ie counters which roll over rapidly) in order that > their first "real" use would not return truly bogus values. Ok, this explanation makes sense. When I ported the FreeBSD timecounter implementation to RTEMS I was a bit surprised how many chips (even a Cortex-M has nothing out of the box) lack a simple free running counter. Maybe it should be added as a comment to these two tc_get_timecount() calls? -- Sebastian Huber, embedded brains GmbH Address : Dornierstr. 4, D-82178 Puchheim, Germany Phone : +49 89 189 47 41-16 Fax : +49 89 189 47 41-09 E-Mail : sebastian.huber@embedded-brains.de PGP : Public key available on request. Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.help
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