[time-nuts] First success with very simple, very low cost GPSDO
albertson.chris at gmail.com
Fri Apr 11 04:33:36 UTC 2014
On Thu, Apr 10, 2014 at 4:52 PM, Bob Stewart <bob at evoria.net> wrote:
> FWIW, I set the DAC to midpoint and use a binary search to get to
> frequency. On my system, I start off with a change of 0x80 and work my way
> down to 0x04 in powers of 2 (0x80, 0x40, 0x20, etc). Once I get to 256
> seconds between DAC changes, I light the PLL fuse. I could probably get
> away with less than 256 seconds. Before I built the TIC, I worked down to
> 0x01 which resulted in pretty long times between changes.
The point i not how to search but how to know if the current frequency is
larger or smaller then the desired 10MHz WITHOUT counting all 10,000,000
The proposal was that could let the timer overflow many times, ignore those
overflows and I need to look only at the last 5 or 6 bits of the timer
after the PPS interrupt. I agree now that I can, under tightly limited
conditions, but I claim in your case, while doing a binary search I must
count all 10,000,000 cycles.
So at each cycle in your binary search what data do you need to decide if
the frequency is high or low?
Redondo Beach, California
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