time synchronization service interface and preemptiongrouper.ieee.org/groups/802/3/br/public/2014-09...

│ mobile automation │ embedded systemsautomotive │ mobile automation │ embedded systemsautomotive

Time Synchronization Service Interface

and Preemption

Christian Boiger

[email protected]

IEEE 802.1 Interim

September 2014

Ottawa, Canada

│ mobile automation │ embedded systemsautomotive

Overview

• The first version of this presentation is outdated due to discussion

happening during the IET meeting on Tuesday.

• This is an updated version. The last slides try to reflect some of

the discussed solutions.

11 September 2014 IEEE 802.1 TSN TG - Ottawa, Canada 2

http://www.ieee802.org/1/files/public/docs2014/as-boiger-TSSI-and-Preemption-0914-v01.pdf


Overview

• The Time Synchronization Service Interface (TSSI) was defined in IEEE 802.3bf.

• IEEE 802.1AS is currently not using the TSSI features.

• It was explicitly mentioned in the IEEE 802.1ASbt PAR to add this interface to IEEE 802.1AS („Incorporation of the interfaces specified in IEEE Std 802.3bf into the IEEE 802.3 full-duplex media-dependent layer model.”)

• TSSI indicates the reception or transmission of a SFD to the higher layer.

• It is currently not defined how this indication is exactly used by IEEE 802.1AS.

• It seems to be necessary to modify the TSSI specification in order to support preemption.

• As Preemption and time synchronization will be used in the same network they need to interoperate.



Assumptions

• TSSI currently seems to indicate only the reception of “normal” SFDs. In order to

interoperate with preemption, TSSI would need to indicate IET SMDs.

• The IET SMDs also include non initial fragment SMDs (SMD-Cx). There seems to

be no need to indicate the start of non initial fragments, therefore this

presentation assumes that non initial fragments are not indicated by the TSSI



Transmit


MAC Merge Layer

eMAC(high priority)

pMAC(low priority)

TimeSync Client

gRS

PLS_DATA.request

PLS_DATA.request

MA_DATA.requestMA_DATA.request

PLS_DATA.request

TS_TX.in

dicatio

n

MAC Client


Transmit Example

Without Preemption:

MA_DATA.request:

Transmitted:

TS_TX.indication:

With Preemption:

eMAC:MA_DATA.request:

pMAC:MA_DATA.request:

Transmitted:

TS_TX.indication:


1 2 Sync3 4

1 2 3 S4

1 2 Sync3 4

1 23

S4

1 2 3 S4

1 2 3 S4


Receive


MAC Merge Layer

eMAC(high priority)

pMAC(low priority)

TimeSync Client

gRS

PLS_DATA.indication

PLS_DATA.indication

MA_DATA.indicationMA_DATA.indication

PLS_DATA.indication

TS_RX

.ind

ication

MAC Client


Receive Example

Without Preemption:

MA_DATA.indication:

Received:

TS_RX.indication:

With Preemption:

eMAC:MA_DATA.indication:

pMAC:MA_DATA.indication:

Received:

TS_RX.indication:


1 2 Sync3

1 2#1 Sync3 2#2

1 23

S

1 2 S3

1 2 3 S

1 32 S


Issue

• IET provides two MAC interfaces, but TSSI provides only one set of TSSI indications. This makes the TSSI indications ambiguous.

• Indications of frames transmitted by the pMAC might arrive after one or more indications of eMAC frames.

In order to match the corresponding frames and indications, it would be necessary to check if the pMAC has finished its transmission and is ready to transmit another frame. In that case the last indication would correspond with this frame (as long as the pMAC frame is not preempted)

• Indications of frames received by the eMAC (and pMAC if the frames get preempted) cannot be associated with each other.

• The solution to this might not be within our scope, if we decide that this is a real issue, we might need to talk to 802.3.



Possible Solutions

• It is guaranteed that PTP event frames

• are never preempted,

• use only the pMAC and

• the knowledge of the status of the transmission (transmission

finished) is available.

• TSSI only indicates the transmission of SMDs of one MAC (configurable

or only pMAC?)

• There are two sets of TSSI indications, one for each MAC

• Other?



Solutions Discussed in IET (1)

Two sets of indications, one for each MAC.


MAC Merge Layer

eMAC(high priority)

pMAC(low priority)

TimeSync Client

PHY

TS_RX

.ind

ication

MAC Client

TSSI

TS_TX.in

dicatio

n

TS_RX

.ind

ication

TS_TX.in

dicatio

n


Solutions Discussed in IET (2)


MAC Merge Layer

eMAC(high priority)

pMAC(low priority)

TimeSync Client

PHY

TS_RX

.ind

ication

MAC Client

TSSI

TS_TX.in

dicatio

n

One set of indications with parameters distinguishing between eMAC and pMACframes.

TS_TX.indication(SMD)

TS_RX.indication(SMD)

SMD:

SMDE_DETECTED

SMDS_DETECTED


Transmit Example

Without Preemption:

MA_DATA.request:

Transmitted:

TS_TX.indication:

With Preemption:

eMAC:MA_DATA.request:

pMAC:MA_DATA.request:

Transmitted:

pMAC:TS_TX.indication:

eMAC:TS_TX.indication:


1 2 43

1 2 43

1 2#1 43 2#2

1 23

4

1 2 43

3

1 2 4


Receive Example

Without Preemption:

MA_DATA.indication:

Received:

TS_RX.indication:

With Preemption:

eMAC:MA_DATA.indication:

pMAC:MA_DATA.indication:

Received:

pMAC:TS_RX.indication:

eMAC:TS_RX.indication:


1 2 43

1 2#1 43 2#2

1 23

4

1 2 43

3

1 32 4

1 2 4


automotive │ mobile automation │ embedded systems

Thank You


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