Precise time synchronization via wifi interface (intel AX201 iwlwifi driver)

Precise time synchronization via wifi interface (intel AX201 iwlwifi driver)

[Wei Liu]

Hi,

I am trying to achieve precise time synchronization via wifi interface.

I used intel AX201 card, certified with TimeSync, 802.11v, mc. So I 
assume it has the capability to do hardware time stamp when running 
applications like linux ptp (http://linuxptp.sourceforge.net/) and gptp 
(https://github.com/Avnu/gptp). However I get error that seems to 
suggest the timestamp mode is not supported.

After reading some source code, I discover that the /ptp4l/ application, 
or /gptp/, or /ethtool/ /-T/ , they all use a system call /ioctl/, which 
uses ethtool_ops call back to determine whether the hardware can do 
software/hardware timestamp.

However when searching in the driver/net/wireless/iwlwifi directory, I 
don't see anywhere /ethtool_ops/ is being implemented in the driver. So 
this most likely is why all user space tools I tried seem to determine 
the card cannot do hardware and also software (driver level) transmit 
timestamp.

Can someone tell me how I could run ptp like application to fully make 
use of the Timesync feature of intel card?

Some more details below:

root@localhost:/debug/tracing# ethtool -i wlp2s0
driver: iwlwifi
version: 5.4.6-050406-generic
firmware-version: 48.4fa0041f.0
expansion-rom-version:
bus-info: 0000:02:00.0
supports-statistics: yes
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

root@localhost:/debug/tracing# ethtool -T wlp2s0
Time stamping parameters for wlp2s0:
Capabilities:
         software-receive      (SOF_TIMESTAMPING_RX_SOFTWARE)
         software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
PTP Hardware Clock: none
Hardware Transmit Timestamp Modes: none
Hardware Receive Filter Modes: none

Re: Precise time synchronization via wifi interface (intel AX201 iwlwifi driver)

[Toke Høiland-Jørgensen]

Wei Liu <wei.liu1011@gmail.com> writes:

> Hi,
>
> I am trying to achieve precise time synchronization via wifi
> interface.

Erm, good luck with that? :)

You do realise that there's a whole bunch of stuff going on below the
driver level (listen-before-send, etc) that makes 'precise' timing (as
in microsecond-accuracy like ptp)... shall we just say challenging?

-Toke

Re: Precise time synchronization via wifi interface (intel AX201 iwlwifi driver)

[Wei Liu]

Hi Toke,

Yes, it is challenging, but IEEE802.1AS already takes consideration of 
IEEE802.11 MAC. So I count on the standardization to take care of the 
challenge :)

Point being that the Intel AX201 card claims Timesync feature 
(https://www.mouser.com/pdfDocs/wi-fi-6-ax201-module-brief.pdf), which 
is based on IEEE802.1AS. So there must be some way to run gptp like 
application on the AX201 intel card.

I appreciate any help here if someone has relevant experiences.

Best,

Wei

On 3/5/2020 12:29 PM, Toke Høiland-Jørgensen wrote:
> Wei Liu <wei.liu1011@gmail.com> writes:
>
>> Hi,
>>
>> I am trying to achieve precise time synchronization via wifi
>> interface.
> Erm, good luck with that? :)
>
> You do realise that there's a whole bunch of stuff going on below the
> driver level (listen-before-send, etc) that makes 'precise' timing (as
> in microsecond-accuracy like ptp)... shall we just say challenging?
>
> -Toke
>