[time-nuts] IEEE 1588 PTP support on raspberry pi 4 compute

[Tim S]

Thanks tvb for your patience,

Hi John,

Yes, I already pre-ordered one and a base-board, I'm hoping someone bulk
buys and then distributes the Lite/8GB version, currently only available if
you order 200x (~$14K-USD total).

I'm very excited about the PCIe being exposed on this version!

        I'm going to seeing about building a variant of this board (
https://www.teradak.com/products/115.html) with improved oscillators for
the CPU (Connor-Winfield TB514-054.0M @ 54MHz), NIC (Connor-Winfield
T604-025.0M 25MHz), and another for I2S audio clocking (IQD Frequency
Products LFTVXO072344 @ 24.576MHz) - IDT 5PB1213's to distribute the clocks
to the FPGA, and others.  For timebase, two ZED-F9T for self referencing
(dual antenna measured/fixed distance, reduce solution error), and an FPGA
to align the 3x clocks to 1PPS and each-other so that the CPU/NIC/Audio
buffers don't get starved.  Large heatsink and active cooling - taking into
account that there is less ground plane in the CM4 so thermal throttling is
more likely.  Primary SMPS ahead of linear LDOs, and then capacitance
multiplier (active RC+BJT low-pass) to snuff power rail noise.  Probably
about 10x the cost for the custom baseboard than the CM4.
        For the sake of he reader's amusement and context, this target is
for a vehicle head unit (car stereo), but I need precise position data and
a stable 24.576MHz master audio sample clock and 30Hz camera frame trigger
clock (I2S LR-clock divided by 6400) for a vehicle data-logger, all content
referenced to a national time standard.  Another (Nvidia) module is
collecting the video data, ambient audio, 3x CAN-bus telemetry, and vehicle
dynamics (gyros/accelerometers).  That module also has an IEEE 1588v2, and
will get a copy of the 25MHz GPSDO clock.  Linux with Preempt-RT on both
modules, CM4 running a VM of Android for display.

I've been working on side-extrication of quantization information from the
F9T unit, this has been a long running RE effort.  Some success in getting
at internal clocks and data lines, which has not been easy at all.  I'm
hoping I'll be able to get at their algorithms and code so that I can
inject some code to feed forward some quantization data over the existing
serial link - but I may have another year or so of poking at uBlox silicon
to get anywhere with that.

-Tim

On Tue, Oct 20, 2020 at 5:10 PM <time-nuts-request at lists.febo.com> wrote:

> From: John De Witt <jhdewitt at gmail.com>
> To: time-nuts at lists.febo.com
> Subject: [time-nuts] IEEE 1588 PTP support on raspberry pi 4 compute
>         module
> Message-ID: <F76219E6-38F1-4119-9C16-4E2745E3C645 at gmail.com>
> Content-Type: text/plain;       charset=utf-8
>
> First post, please be patient with me. Reading the list for a handful of
> years and grateful to the community.
>
> Am interested in low cost GNSS time source to keep clocks during internet
> outage.
>
> Just read that compute module raspberry pi 4 supports IEEE 1588 Precision
> Time Protocol.
>
> Exciting to me ~25usd base for microsecond or better performance over
> network.
>
> Anyone planning on using this? Ethernet is handled by BCM54210 which
> states in data sheet: ?IEEE 1588v2 compliant ? One-step or two-step clock ?
> On-chip timestamping?
>
> Thinking of pairing it with ZED-F9P with PPS would be fun to have PTP GPS
> stratum 1 on LAN for cheap. Ok enough rambling thank you have a nice day.
>
>