[time-nuts] First success with very simple, very low cost GPSDO, under $8

Orin Eman orin.eman at gmail.com
Wed Apr 9 23:25:46 EDT 2014


On Wed, Apr 9, 2014 at 11:03 AM, Chris Albertson
<albertson.chris at gmail.com>wrote:

> On Wed, Apr 9, 2014 at 2:08 AM, Hal Murray <hmurray at megapathdsl.net>
> wrote:
>
> >
> > > Also any code that accesses them needs to do so with interrupts turned
> > > off...  otherwise you can wind up with corrupted values.
> >
>
> Forgot if I made this point but in a GPSDO when the interrupt is caused by
> the PPS, the interrupts are in effect off for 0.99999 seconds after each
> interrupt.   The software can assume an interrupt will never happen less
> then one second after an interrupt.  So the software does all the variable
> access within millisecond after each interrupt.
>
> These micro controllers are actually much easier to deal with than a
> general purpose multi-tasking operating system.  There is far less
> non-determinism.



Indeed.  I was just thinking the same thing.  It's much easier to deal with
an interrupt routine updating variables than multiple threads fighting over
them...   I just had to replace a mutex lock with an atomic exchange to
avoid a deadlock in my code at work.

Orin.


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