Re: [Linuxptp-users] Question about meanPathDelay (possible bug?)

[Wolfgang W. <wol...@gm...>]

On Tue, 30 Jul 2013 17:46:58 +0200, Miroslav Lichvar <mli...@re...>  
wrote:

> On Tue, Jul 30, 2013 at 03:06:28PM +0200, Wolfgang Wallner wrote:
>> I'm not sure, but I think the "receiveTimestamp of Delay_Resp
>> message"-part is not implemented correctly in LinuxPTP.
>>
>> The function process_delay_resp() calls clock_path_delay() as follows:
>>
>> 	clock_path_delay(p->clock, p->delay_req->hwts.ts, m->ts.pdu,
>> m->header.correction);
>>
>> The third argument is used by clock_path_delay() as what is called t4 in
>> the standard.
>> As far as I understand the code, the third argument (m->ts.pdu) is the
>> ingress timestamp on the slave of the DelayResp-message.
>> But I think what should be passed here should be the ingress timestamp  
>> on
>> the master of the DelayReq-message, which is contained in the
>> "receiveTimestamp"-field of the DelayResp-message  
>> (rsp->receiveTimestamp).
>
> To me, it seems it's the DelayResp receiveTimestamp in the ts.pdu
> field and used as t4 in the delay calculation. It's filled by the
> following code in the msg_post_recv() function.
>
>         case DELAY_RESP:
> 		timestamp_post_recv(m, &m->delay_resp.receiveTimestamp);

Oh, thanks for making this clear :)

>
> Why do you think it's the ingress time of the DelayResp message?

Because at first I misinterpreted the standard. When it says  
"receiveTimestamp of Delay_Resp message" I thought of the Ingress  
timestamp of DelayResp.
I was confused, and had a look at the source code of LinuxPTP. I found  
"m->ts.pdu", which at first looks like a timestamp assigned by a lower  
layer, e.g. the ingress timestamp.
I did not think of the possibility that the lower layer puts the value of  
delay_resp.receiveTimestamp into this field.

Sorry for broadcasting my confusion, I should have dug deeper in the code  
:)

Thanks for clearing this up,
Wolfgang