Date: Wed, 7 Jul 1999 21:36:50 +0200 (SAT) From: John Hay <jhay@mikom.csir.co.za> To: davids@webmaster.com (David Schwartz) Cc: stable@FreeBSD.ORG Subject: Re: PPS API change assert/clear Message-ID: <199907071936.VAA06015@zibbi.mikom.csir.co.za> In-Reply-To: <000f01bec8aa$bc9bb870$021d85d1@youwant.to> from David Schwartz at "Jul 7, 1999 11:58:44 am"
next in thread | previous in thread | raw e-mail | index | archive | help
Do you mean that if you measure the voltage on the DCD pin and it go from negative to positive (ASSERT) you get a CLEAR from the software? That is wrong and not what I see here. Do you have version 1.224.2.6 of sio.c? I know it has been broken in versions before that in stable and versions before 1.246 in current. John -- John Hay -- John.Hay@mikom.csir.co.za > > Wow. It seems you're right. This still makes no sense to me, but it does > seem to be the standard! > > When DCD is asserted, you will get a clear event. When DCD is cleared, you > will get an assert event. Go figure: > > A PPS signal consists of a series of pulses, each with an > ``asserted'' (logical true) phase, and a ``clear'' (logical false) > phase. The two phases may be of different lengths. The API may > capture an ``assert timestamp'' at the moment of the transition into > the asserted phase, and a ``clear timestamp'' at the moment of the > transition into the clear phase. > > The specific assignment of the logical values ``true'' and ``false'' > with specific voltages of a PPS signal, if applicable, is outside the > scope of this specification. However, these assignments SHOULD be > consistent with applicable standards. Implementors of PPS sources > SHOULD document these assignments. > > --------- > Reminder to implementors of DCD-based PPS support: TTL and > RS-232C (V.24/V.28) interfaces both define the "true" state as > the one having the highest positive voltage. TTL defines a > nominal absence of voltage as the "false" state, but RS-232C > (V.24/V.28) defines the "false" state by the presence of a > negative voltage. > --------- > > DS > > > > > > > > > It seems that the logic of assert and clear have changed. > > > Now an assertion > > > > of DCD is considered a clear, and vice-versa. Why was the > > logic broken? > > > > > > > > > > The PPSAPI draft was clarified and we were the odd ones out, so > > we changed > > > to be compatable to the rest. > > > > That makes no sense. I know Linux is currently the same way > > FreeBSD was. > > Can you send me a copy of this 'clarification'? > > > > I can't understand how this can possibly make sense. I now > > get a 'CLEAR' > > event whenever I assert DCD and an 'ASSERT' event whenever I clear DCD. > > > > DS To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199907071936.VAA06015>