Re: [time-nuts] precision timing pulse
chris@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 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.
On Wed, Nov 16, 2016 at 1:03 PM, Hal Murray hmurray@megapathdsl.net wrote:
chris@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
On 11/16/16 1:03 PM, Hal Murray wrote:
chris@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 teensy from PJRC is a good example - uses the Arduino dev
environment and has all the easy to use libraries, but is a LOT faster
and has better peripherals. Or you can use other dev environments. It's
an ARM Cortex something or other.
<$20
The BeagleBoard Black is a bigger, more capable example.. You can
actually run a *nix on it, but has device drivers and such for lots of
GPIO and timers.
On Wed, 16 Nov 2016 20:47:52 -0800
jimlux jimlux@earthlink.net wrote:
The BeagleBoard Black is a bigger, more capable example.. You can
actually run a *nix on it, but has device drivers and such for lots of
GPIO and timers.
And additionally has two PRU units, which are basically uC's with
cycle exact execution, that can toggle all their GPIO (up to 16 IIRC)
at each cycle and run with up to 200MHz.
But then, for most things, the BBB is a bit of an overkill :-)
Attila Kinali
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the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson