[time-nuts] Frequency counter questions

Bob kb8tq kb8tq at n1k.org
Mon Apr 24 18:42:16 EDT 2017


> On Apr 24, 2017, at 3:49 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> 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.
> -- 
> C
> The STM32 is in fact a low level micro controller that does not run an OS.

The STM being discussed is what they call an F7 part. A representative 
board running it is (= the one here on my desk):

http://www.st.com/en/evaluation-tools/32f769idiscovery.html <http://www.st.com/en/evaluation-tools/32f769idiscovery.html>

It’s a board with 128 Mb of RAM and 512 Mb of flash. Among the other stuff on 
there is an RJ-45 ethernet jack There are a variety of RTOS options available
along with some cut down Linux versions. Trying to do ethernet without at least
an RTOS does not make much sense. It’s what they are calling an Cortex-M7 rather than
a Cortex M4. There are a number of similar boards. If it’s an STM 32F7, the features
on the board will be similar to the one sitting here. 

Indeed the term STM32 covers a lot of ground and we have zigged and zagged 
a bit. Repeating all of the details from every earlier post in the thread makes
things even longer than they already are. Some amount of abbreviation is


> 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.
> ...ebay.com/itm/New-STM32F103C8T6-ARM-STM32...
> <http://www.ebay.com/itm/New-STM32F103C8T6-ARM-STM32-Minimum-System-Development-Board-Module-For-Arduino-/272546586490?hash=item3f750adf7a:g:RakAAOSwUKxYlyHv>
> hris Albertson
> Redondo Beach, California
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