[time-nuts] Re: Network interface cards that support timestamping

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Hey John,

as far as I'm aware, there are a few Ethernet ICs which do have hardware 
pins for PTP purposes. The Broadcom BCM54210PE comes to mind as used on 
the Raspberry Pi CM4 (not the regular Raspberry Pi 4, the Compute 
module, they use different Ethernet PHYs). I believe the Intel i225 also 
has dedicated Pins for PTP, but can't find the datasheet I once obtained 
to make sure. IF these pins however are accessible on the typical NIC 
(as in plugin card, not just the silicon chip itself) depends very much 
on who did the design. The abovementioned Raspberry pi CM4 has two 
dedicated pins available, directly wired to the appropriate pins of the 
PHY chip, but driver support is not entirely there yet last I heard.

For generic off-the-shelf i210/i225 cards, I have yet to come across one 
which has documented hardware pins for PTP purposes, but the sample size 
is rather small (four or five different cards in total...).

Judging from a "grep -r TX_HARDWARE ./*" in Linux kernel tree there seem 
to be a few drivers which support hardware timestamping of some sort, so 
my first guess would be that those coming up there could potentially 
have pins which can be used for timestamping purposes. There might be 
more as not everyone is publicly documenting their chips in a way that's 
actually useful, but at least it's a start.

HTH,
Florian

On 30.01.23 19:15, John Miller via time-nuts wrote:
> Hey All,
> I'm curious as to what the collective experience is amongst this group when it comes to feeding a timestamp signal into a NIC, either for PTP purposes or for as a normal PPS refclock. The Intel i210 PCIe network card has a few software defined pins that can be used for this purpose, and the chrony documentation has some information about it:
> 
> https://chrony.tuxfamily.org/examples.html#_server_using_reference_clock_on_nic
> 
> I imagine most of us here use traditional RS232 serial ports to get this signal into an x86 computer, usually using the DCD pin. I've found some implementations of RS232 on PCs don't implement all of the additional signaling pins, so sometimes DCD is flat out missing. In other cases - especially with smaller embedded-type boards only UARTs with Rx/Tx are available to the user. (I'm fiddling with using GPIO pins on a few such systems, but it's quite a struggle.) So, there is a need for getting PPS signals into systems.
> 
> There are also highly specialized network interface cards, such as this one: https://www.ebay.com/itm/404117321209
> 
> ... which does explicitly support PTP timestamping, but it's not clear to me if it could pull in a "standard" PPS signal to be made available to chrony or NTPsec. I haven't found much documentation on the NT20E2 yet, unfortunately, and it may simply not exist for hobbyists.
> 
> Does anyone here know if any other network cards that support software defined pins, like the i210 does, or any other methods for getting a PPS signal to be fed into a PC, and of course interpreted correctly?
> 
> Thanks!
> John
> 
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