[time-nuts] Frequency counter questions

Chris Albertson albertson.chris at gmail.com
Mon Apr 24 15:49:44 EDT 2017

On Mon, Apr 24, 2017 at 10:13 AM, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
> Some of the process below is “not trivial”. One example:
> You have a “gate” from the GPSDO and a “signal” from somewhere else. If you
> want the STM to do the whole thing, the “gate” pin needs to get the job
> done in
> X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) isn’t a
> problem. Having a
> > +/- 1 cycle delay *is* a problem. The interrupt servicing structure in
> the MCU
> may or may not be able to hit things +/- 10 ns or even +/- 100 ns.
> Sometimes a
> “lower power” MCU with simple code is better at this than a multi core
> gizmo running
> a high level operating system.



The STM32 is in fact a low level micro controller that does not run an OS.

The chips contain counters and other hardware so most of the real-time
stuff is not done in software.  You need to set this up so the on-chip
hardware outside of the CPU is used.

There are two basic types of ARM computers, the "Cortex A" is what is in
your phone and these have multi cores, GHz class clock speeds, gigabytes
class memories and run an OS.   The other is ARM "Cortex M".  These are
much smaller and run on about 100 uA of current with clocks about 100 MHz
and kilobyte class memories and don't support running an OS.  These are
used in embedded applications such as the throttle control in your car or a
high end battery charger.  These cost about $1 each and the physical chip
is about 3/8 inches square.    I buy them quality one as a "Nucleo" board
for about $12.  It is like an Arduino but about (literally) 100X better
specs and half the cost.  About the same physical size.    But for this
counter project I'd use a generic STM32 board from eBay.  They sell for
about $2 shipped

Take a look at this device.  It has a lot of power.  It can even be
programmed using the Arduino IDE or the gnu toolchain and others.  You
can't beat the price or the size.

hris Albertson
Redondo Beach, California

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