[time-nuts] Re: Can Anyone Help Me Get PPS Into This Mini PC?

Magnus Danielson magnus at rubidium.se
Wed Feb 14 17:22:43 UTC 2024 

Hi,

Speaking of which. Many have realized that normal PCs and servers don't 
have any aspect of stellar timing performance. Several have developed 
time cards, and now Facebook/META initiated IEEE standardization as IEEE 
P3335. Me and Joe Gwinn is time-nuts active there, maybe some more.

Cheers,
Magnus

On 2024-02-13 21:13, Bob Camp via time-nuts wrote:
> Hi
>
> Like it or not, pretty much all these small (and many not so small)  MCU’s are a bit challenged in terms of single digit nanosecond time capture. It simply isn’t a design priority for these folks. If the hardware is challenged, then whatever goes on top of that will simply add more issues.
>
> If you really need single digit sort of accuracy, some sort of outboard “gizmo” is likely to be part of the design.
>
> At this point it is a bit unclear if the goal is +/- 1 ns accuracy. +/- 10 ns resolution, or something else entirely different. There’s a really wide range between those two limits. Both *might* be called “I need nanoseconds”.
>
> If the goal is something like the PPS pulse out of a typical modern GPS module, a goal below 200ps accuracy just might be what somebody would look for. That (at least to me) would be well outside the “I need nanoseconds” range. Once you add a TDC, it’s not that much harder than 2 ns accuracy.
>
> Bob
>
>> On Feb 12, 2024, at 7:17 PM, Ed Marciniak via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> Depending on the exact architecture of an embedded PC, a serial port might have hundreds of nanoseconds jitter added by a PCIe switch or things like an LPC interface that maps to a 16 bit 8.33 MHz bus in between.
>>
>> In an ideal world, a network interface with IEEE-1588 PTP support would directly get a PPS to synchronize a counter
>> ________________________________
>> From: Denis Dowling via time-nuts <time-nuts at lists.febo.com>
>> Sent: Monday, February 12, 2024 5:14:06 PM
>> To: time-nuts at lists.febo.com <time-nuts at lists.febo.com>
>> Cc: Denis Dowling <dpd at opsol.com.au>
>> Subject: [time-nuts] Re: Can Anyone Help Me Get PPS Into This Mini PC?
>>
>> Hi Ed,
>>
>> I can see how you would want something like this to replace the RPi as
>> it looks a lot more capable. There does not seem to be a lot of
>> information about the GPIO port on this board. From previous experience
>> with Advantech equipment the GPIO ports can be difficult to find
>> information on. A better option would be to use the COM port also on the
>> board. This is likely mapped to /dev/ttyS0 on boot. You might have to
>> enable it in the BIOS first. It should then be possible to use the RS232
>> handshake lines for the PPS input to the Linux pps-tools. You can also
>> feed in GPS NMEA to this same communication port that will mean no
>> external NTP connections are needed.
>>
>> Regards,
>> Denis
>>
>>
>> On 10/02/2024 9:10 am, Ed Armstrong via time-nuts wrote:
>>> I recently purchased one of these mini PCs to be used as my router.
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__cwwk.net_products_cwwk-2Dx86-2Dp5-2Dsuper-2Dmini-2Drouter-2D12th-2Dgen-2Dintel-2Dn100-2Dddr5-2D4800mhz-2Dfirewall-2Dpc-2D2x-2Di226-2Dv-2D2-2D5g-2Dlan-2Dfanless-2Dmini-2Dpc-3Fvariant-3D44732374352104&d=DwIGaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=JsDsKeR7cZC8wbZhIlxxBQ&m=JBs9b5cAEBCI0RcPG_SBLalBkFpA8vxUbfgk7fZGN1gP2uLM8TTE12Ls33A0gRnn&s=9JUsRvAgIvKeYLFylZeCPkwW7ImbHurHBMg3mbTe4Qo&e=
>>>
>>>
>>>
>>> I am going to be running the new 64-bit Intel release of the excellent
>>> "Tomato" router firmwareTomato64 <https://urldefense.proofpoint.com/v2/url?u=https-3A__tomato64.org_&d=DwIGaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=JsDsKeR7cZC8wbZhIlxxBQ&m=JBs9b5cAEBCI0RcPG_SBLalBkFpA8vxUbfgk7fZGN1gP2uLM8TTE12Ls33A0gRnn&s=HkPJNn78J7mrok__SJQFksbEuxiR87zBhndqPpe8VGo&e=>, which can be
>>> installed either "bare-metal" or as a virtual machine. I am going the
>>> virtual machine route using proxmox v8.1.3. The tiny PC idles at about
>>> 9 W and maxes out around 18 W, and has considerably more power than I
>>> need for my routing purposes. So, I also put my FreePBX on a separate
>>> virtual machine, also located on this mini PC. But that is probably
>>> not very interesting to anyone here, nor is it really part of my
>>> question.
>>>
>>> Proxmox is a Linux based OS which is designed for the express purpose
>>> of running virtual machines. I suspect many of you on this mailing
>>> list may already be using it yourself. I am currently running my own
>>> stratum one NTP server on a Raspberry Pi 3 which is getting its PPS
>>> from a GPSDO. well, proxmox comes with chrony already installed, and
>>> I'm sure I could change it over to ntpd if I wished to do so. If any
>>> of you follow my first link, you will see the little mini PC has a
>>> header for GPIO. It is a 2x5 header with I believe a 2 mm pitch.
>>> According to the listing, there are four input and four output pins. I
>>> assume the other two pins are either both grounds or both positive,
>>> not really sure.
>>>
>>> Now comes my question. Can any of you tell me how to use these GPIO
>>> pins? I can find tons of information very easily on setting this thing
>>> up as a router, NAS, or as a desktop computer. I have not been able to
>>> find a single post related to those GPIO pins. I can't find the pin
>>> out, can't find out what voltage they are supposed to work at, nor any
>>> information about communicating with them in Linux. I queried the
>>> system, hoping I could look up the motherboard online, and this is
>>> what I got:
>>>
>>> root at Proxmox:~# dmidecode -t 2
>>> # dmidecode 3.4
>>> Getting SMBIOS data from sysfs.
>>> SMBIOS 3.6.0 present.
>>> # SMBIOS implementations newer than version 3.5.0 are not
>>> # fully supported by this version of dmidecode.
>>>
>>> Handle 0x0002, DMI type 2, 15 bytes
>>> Base Board Information
>>>         Manufacturer: Default string
>>>         Product Name: Default string
>>>         Version: Default string
>>>         Serial Number: Default string
>>>         Asset Tag: Default string
>>>         Features:
>>>                 Board is a hosting board
>>>                 Board is replaceable
>>>         Location In Chassis: Default string
>>>         Chassis Handle: 0x0003
>>>         Type: Motherboard
>>>         Contained Object Handles: 0
>>>
>>> root at Proxmox:~#
>>>
>>> I also tried dmidecode -t baseboard, this obviously gave more details,
>>> but most devices were just listed as "other". I haven't found this to
>>> be terribly useful.
>>>
>>> My desire is to replace the Raspberry Pi by syncing chrony or ntpd to
>>> the PPS in proxmox and using that instead. It would save a tiny amount
>>> of energy, and would remove the slight jitter caused by the ethernet
>>> port being on USP, I believe. Can anybody on here give me some idea on
>>> how to do this, or perhaps point me in the right direction to find the
>>> information I need.
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