[time-nuts] precision timing pulse

Chris Albertson albertson.chris at gmail.com
Wed Nov 16 22:30:43 EST 2016

On Wed, Nov 16, 2016 at 1:03 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> chris at chriscaudle.org said:
> > but once you get to most of the ARM processors it is harder to make them
> > deterministic because of caches.
> There are many ARM SOC chips that are half way between an Arduino and a
> Raspberry Pi.  They have GPIO and various serial ports and counter/timers.
> They don't have USB, Ethernet, or a display controller.  They do have
> on-chip
> RAM and Flash.

The big divide with ARM is the "A" and "M" kind.    The ARM A is what you
have inside your cell phone and what is used in the Raspberry Pi and most
counters and set top boxes and the like.   Typically this run an operating
system mostly Linux.

The Arm Cortex M is a micro controller.  There are different kinds, they
are 32 bits and some have floating point hardware, some don't but they are
all designed for low power use.   You can buy an ARM Cortex M0 on a PCB
that is almost as easy to use as an Arduino for about $4.00 shipped.

ARM has a huge range of performance, one of mine is a quad core A7 running
at 1.4GHz and uses about 1.5 amps of power another is an M0 that runs at
8Mhz nominal but I can make it sleep (stop the clock) and run it off
battery power for a long time.     The performance range is about the
largest I know of

The low power Cortex M chips are sized as described below.  But the A chips
can have a gigabyte of RAM and almost zero flash

One reason for this is the at the ARM architecture is licensed to many
manufacti=urers and they all need to "be different"

> The ones I worked with didn't have a cache.  The on-chip SRAM was good
> enough.
> They typically came with 3 sizes of on-chip memory, growing by a factor of
> 2
> each step.  So you get things like
>   16K RAM, 64K Flash
>   32K RAM, 128K Flash
>   64K RAM, 256K Flash
> That was 5-10 years ago, so things have probably changed.  I'd be surprised
> if something similar wasn't available today.  I haven't looked for eBay
> style
> low cost boards.
> --
> These are my opinions.  I hate spam.
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Chris Albertson
Redondo Beach, California

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