[time-nuts] Designing an embedded precision GPS time server

Iain Young iain at g7iii.net
Thu Oct 26 17:26:02 EDT 2017


On 26/10/17 22:11, Chris Caudle wrote:

> The processor you mentioned has a Cortex-M7 at 300MHz.  BBBB has a
> Cortex-A8 running at 1GHz plus a Cortex-M processor available as a
> coprocessor. Peripheral set is pretty comparable, and you can buy BBB at
> retail for $50 which gets you the faster higher class processor, 512MB of
> DRAM and 4GB of flash.  It runs linux right out of the box so you
> basically  power it on and have NTP running.

The BB Green is even better value for money, and why would we need HDMI
for timing apps ? (It also simplifies doing my Poor man's TIC!)

> On my list of projects to work on is a cape for BeagleBone Black that
> takes 10MHz and 1PPS inputs along with a couple of RS232 converters for
> the UARTs so you can connect a GPSDO to a BBB to make a time server.  In
> my estimation that seemed like the best return on effort.

Wheen you get around to it, *Please* consider:

    1) multiplying that 10MHz up to 24 MHz as an option
    2) RS422 option instead of RS232 (for the Lucent/HP GPS/Rb boxes)
    3) PPS routed to TIMER4/5/6/7 rather than any old GPIO
    4) Cover _all_ UARTS, even if serial headers are needed, rather than
9-pin D connectors
    5) Some method of dropping a 5V PPS down to 3.3V (2N2222 comes to
mind, as does a /2 voltage divider [2.5V is sufficient to trigger the
GPIO pins], I have done both - and yes measured the delay through the
2N2222!)

(Sorry Chris, I was looking at the serial cape options earlier today
to try an santise my lash-ups, and was most disappointed!)


Iain



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