Re: [Linuxptp-users] Linuxptp - Supported Hardware

[Wolfgang H. <wh...@xi...>]

Just as a data point, I used the DP83640 PHY in the past and got about 
10ns, measured as the uncertainty in time-of-flight style physics 
experiments. The PHY only supports 10/100M Ethernet, but is working with 
LinuxPTP and can output synchronized clocks and triggers.

Best regards,

Wolfgang


On 9/27/2023 3:34 AM, Fernando Gomes wrote:
> Hi Richard,
>
> Thank you very much for your reply! We currently have a PTP 
> implementation done on an FPGA but we are looking for an alternative 
> without using an FPGA on simpler products. With the current 
> implementation, we usually have an accuracy better than 100ns (most of 
> the time at around 60ns), this is why I was considering the PHY 
> tagging, to try to have the best possible accuracy when using a CPU to 
> implement PTP, but I don't know what accuracy is possible when the 
> timestamping is done at the MAC level and at the PHY level, do you 
> know if there is any benchmark about that? I saw some numbers on a 
> discussion saying that they had an accuracy of about 200ns with MAC 
> level timestamping, but having more consistent data will be great, 
> 200ns might not be acceptable for our application, we are going to do 
> a proof-of-concept to validate the results, but if we know beforehand 
> the achievable accuracy it could avoid to do extra effort if the 
> required accuracy is not achievable.
>
> Regarding the CPU we are currently evaluating, the ethtool -T results 
> are different on the two ethernet ports, which should be according to 
> their spec since they say they only support TSN in eth0:
>
> ethtool -T eth0
> Time stamping parameters for eth0:
> Capabilities:
>         hardware-transmit
>         software-transmit
>         hardware-receive
>         software-receive
>         software-system-clock
>         hardware-raw-clock
> PTP Hardware Clock: 1
> Hardware Transmit Timestamp Modes:
>         off
>         on
> Hardware Receive Filter Modes:
>         none
>         all
>         ptpv1-l4-event
>         ptpv1-l4-sync
>         ptpv1-l4-delay-req
>         ptpv2-l4-event
>         ptpv2-l4-sync
>         ptpv2-l4-delay-req
>         ptpv2-event
>         ptpv2-sync
>         ptpv2-delay-req
>
>
> ethtool -T eth1
> Time stamping parameters for eth1:
> Capabilities:
>         hardware-transmit
>         software-transmit
>         hardware-receive
>         software-receive
>         software-system-clock
>         hardware-raw-clock
> PTP Hardware Clock: 0
> Hardware Transmit Timestamp Modes:
>         off
>         on
> Hardware Receive Filter Modes:
>         none
>         all
>
> From the ethtool -T results, the eth1 MAC doesn't have PTP-specific 
> Hardware Receive Filter Modes, but it still is capable of 
> doing hardware timestamping at the MAC level, right?
>
> Is it possible to use linuxptp to implement a one-step transparent 
> clock? For example, when using both eth0 and eth1 ports to implement 
> HSR we need the PTP messages passing by the device to be correctly 
> adjusted to have a precise time synchronization of all devices in the 
> network (HSR ring).
>
> Best regards
>
> Fernando
>
>
>
> On Wed, Sep 27, 2023 at 3:47 AM Richard Cochran 
> <ric...@gm... <mailto:ric...@gm...>> wrote:
>
>     On Mon, Sep 25, 2023 at 02:36:35PM +0100, Fernando Gomes wrote:
>
>     > Is there a list of hardware that can be used with linuxptp to do
>     > timestamping at the hardware level (on PHY or on MAC)? There are
>     some phys
>     > that support it, like the Vitesse / Microchip, etc., but is there a
>     > compatibility list available?
>
>     I used to maintain a list of hardware, but I gave that up years ago
>     when the number of products became too large.  Nowadays most new MACs
>     have PTP support.
>
>     The easiest way to find out your MAC's capabilities is:
>
>             ethtool -T eth0
>
>     For PHYs, the main issue is that the Linux networking stack doesn't
>     treat MACs and PHYs equally.  If you really need to use a PTP PHY,
>     then you will likely have to configure and even patch your kernel
>     specifically for your hardware.
>
>     HTH,
>     Richard
>
>
>
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-- 
Wolfgang Hennig, Ph.D.
XIA LLC
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Oakland, CA 94601