# US 2014/0156892 A1 · Method, system, and apparatus for link latency management

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- Number: US 2014/0156892 A1
- Document ID: US20140156892A1
- Status: Published application
- Kind: A1
- Application number: 13/913,774
- Filed: 2013-06-10
- Published: 2014-06-05
- Earliest claimed: 2004-12-13
- Inventors: Tim Frodsham; Michael J. Tripp; David J. O'Brien; Navada Herur Muraleedhara; Naveen Cherukuri; Sanjay Dabral; David S. Dunning; Theodore Z. Schoenborn
- Web page: https://patentgrep.com/patent/US20140156892A1

## CPC

- G06F 1/06: Clock generators producing several clock signals {(G06F1/08 - G06F1/14 take precedence)}
- G06F 13/362: with centralised access control
- H04L 43/50: Testing arrangements
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A link latency management for a high-speed point-to-point network (pTp) is described The link latency management facilitates calculating latency of a serial interface by tracking a round trip delay of a header that contains latency information. Therefore, the link latency management facilitates testers, logic analyzers, or test devices to accurately measure link latency for a point-to-point architecture utilizing a serial interface.

## Claims

### Claim 1

An apparatus to calculate latency of a serial interface by tracking a delay of a header for a point-to-point architecture comprising:
a reference clock;
a transmitter from a master agent, coupled to a network fabric of the point to point architecture, to enter a mode of operation with a known latency from the reference clock to a header packet; and
a receiver from a slave agent, coupled to a network fabric of the point to point architecture, to align a plurality of incoming lanes from the master agent and to calculate a latency based on a clock.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the clock for the slave agent to calculate the latency is a system reference clock that is the closest to the slave agent.

### Claim 3

An apparatus to calculate latency of a serial interface by tracking a round trip delay of a header for a point-to-point architecture comprising:
a reference clock;
a transmitter from a master agent, coupled to a network fabric of the point to point architecture, to enter a loop back mode of operation with a known latency from the reference clock to a header packet;
a receiver from a slave agent, coupled to a network fabric of the point to point architecture, to align a plurality of incoming lanes from the master agent and to calculate a latency based on a clock and to insert a latency calculation into a loop back start packet data payload; and
a master receiver in the master agent to calculate a latency from a reference clock to a header received from the slave.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein the clock for the slave agent to calculate the latency is a system reference clock that is the closest to the slave agent.

### Claim 5

An apparatus to calculate latency of a serial interface comprising:
a master agent to determine a latency of its transmitter based on a reference clock and a header packet;
a slave receiver to determine a latency based on a closest system reference clock; and
a round trip latency to be calculated based on half of a total of the latency for the master latency and a master round trip receive

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the clock for the slave receiver to calculate the latency is a system reference clock that is the closest to the slave receiver and is not the same as the reference clock used by the master agent.

### Claim 7

A system that adheres to a pTp architecture and facilitates calculation of latency for a serial interface comprising:
a dynamic memory, coupled to the serial interface to store data for the system;
a master agent to determine a latency of its transmitter based on a reference clock and a header packet;
a slave receiver to determine a latency based on a closest system reference clock; and
a round trip latency to be calculated based on half of a total of the latency for the master latency and a master round trip receive

### Claim 8 (depends on 7)

The system of claim 7, wherein the pTp architecture adheres to a layered protocol scheme.

### Claim 9

A system that adheres to a pTp architecture and facilitates calculation of latency for a serial interface for outbound and inbound latency comprising:
a master agent to determine a latency of its transmitter based on a reference clock and a header packet;
a slave receiver to determine a latency based on a closest system reference clock; and
a round trip latency to be calculated based on half of a total of the latency for the master latency and a master round trip receive

### Claim 10 (depends on 9)

The system of claim 9, wherein the pTp architecture adheres to a layered protocol scheme.

### Claim 11

An apparatus to calculate latency of a serial interface by tracking a cycle of a packet header for a point to point architecture comprising:
a reference clock;
a transmitter from a master agent, coupled to a network fabric of the point to point architecture, to enter a loop back mode of operation with a known latency from the reference clock to a header packet;
a receiver from a slave agent, coupled to a network fabric of the point to point architecture, to align a plurality of incoming lanes that were received from the transmitter of master agent and to calculate a latency based on a clock and to insert a latency calculation into a loop back start packet data payload; and
a master receiver in the master agent to calculate a latency from a reference clock to a header received from the receiver of the slave agent.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the clock for the slave receiver to calculate the latency is a system reference clock that is the closest to the slave receiver and is not the same as the reference clock used by the master agent.