On 5/17/09 9:24 AM, "Hal Murray" <hmur...@megapathdsl.net> wrote: > > >> In which case, if you're saddled with 32 bit (or 8 bit!) reads, you >> have to do multiple reads, so that by the end of the process, you can >> assure yourself it's consistent. > >> E.g read high, read low, read high, read low So you can check low #1 >> against low #2, and figure out if you had a roll over. > > Why read the low twice? > > I though the normal recipe was to read high, low, high. If the two highs are > the same you know a carry didn't happen so a high/low pair is a valid reading. Yes, but then, if it did happen, then you need to read low again. If you do the 4 reads as a block (say, with interrupts disabled), then you get a nice deterministic timing for the code. In practice, it's just a design decision which way one does it. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-III? Poul-Henning Kamp
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-III? Chuck Harris
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-III? Lux, James P
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-I... Chuck Harris
- Re: [time-nuts] FreeBSD, NetBSD, or Min... Lux, James P
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-III? Poul-Henning Kamp
- Re: [time-nuts] FreeBSD, NetBSD, or Minix-I... Hal Murray
- Re: [time-nuts] FreeBSD, NetBSD, or Min... Poul-Henning Kamp
- Re: [time-nuts] FreeBSD, NetBSD, o... Lux, James P
- Re: [time-nuts] FreeBSD, NetBSD, o... Hal Murray
- Re: [time-nuts] FreeBSD, NetBSD, o... Lux, James P
- Re: [time-nuts] FreeBSD, NetBSD, o... Magnus Danielson
- Re: [time-nuts] FreeBSD, NetBSD, o... Hal Murray
- Re: [time-nuts] FreeBSD, NetBSD, o... Magnus Danielson
- Re: [time-nuts] FreeBSD, NetBSD, o... Hal Murray
- Re: [time-nuts] FreeBSD, NetBSD, o... M. Warner Losh
- Re: [time-nuts] FreeBSD, NetBSD, o... Hal Murray
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- Re: [time-nuts] FreeBSD, NetBSD, o... Tom Van Baak
- Re: [time-nuts] FreeBSD, NetBSD, o... Magnus Danielson
- Re: [time-nuts] FreeBSD, NetBSD, o... Stanley Reynolds