Hi To make things play nice, you would like to have the timer counters reset at a specified point. That way the math all works out nicely.
Bob On Dec 7, 2012, at 12:18 AM, Hal Murray <hmur...@megapathdsl.net> wrote: > > li...@rtty.us said: >> That would be an input capture rather than an interrupt. > > Thanks. Yes, that's the term I was trying to remember. > > > li...@rtty.us said: >> To be useful, you need an input capture that: >> 1) Runs at a fast enough clock (1 GHz would be nice) >> 2) Has enough bits to get to 1 pps (say 32 bits) >> 3) Has a built in period set, so the hardware works without a lot of silly >> stuff > > What do you mean by "period set"? > > (I did a bit of googling, but didn't hit anything close to pay dirt.) > > My expectation is that the counter/timer just counts on the local/CPU clock > or some sub-multiple of that. When the external signal makes a low-to-high > transition, the value in the counter is copied into a holding register and > sets a status bit that may generate an interrupt. The counter just keeps > counting through overflows and such. > > ---------- > > The enough-bits from [2] above can be partially implemented in software. > When the counter overflows, it sets a status bit and maybe generates an > interrupt. The software keeps the high bits in memory. When it sees that > status bit, it bumps that counter. > > Getting everything right is not simple. > > There is a standard recipe for reading a hardware counter that lives in two > registers. You read high, low, high. If the two high readings match, the > answer is (either) high and low. If not, try again. > > Some hardware supports a hack to latch the high when you read the low. > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > 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. _______________________________________________ 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.