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Elasticity Buffer Merged with Start of Message Detection

IP.com Disclosure Number: IPCOM000249845D
Publication Date: 2017-Apr-17
Document File: 4 page(s) / 198K

Publishing Venue

The IP.com Prior Art Database

Related People

Kevin Raymond Driscoll: INVENTOR

Abstract

Most serial communication systems contain receivers, repeaters, and transmitters, each of which may use its own clock that is not completely synced to the other clocks. Elasticity buffers are used to account for differences in frequency between the transmitter's and the receiver's clocks. Further, as the transmitter's clock may be slower than a receiver's or a repeater's, the elasticity buffer is partially filled (typically 50% filled) before the output of the buffer can start being used. In many of these systems, and in particular those that don't maintain Direct Current (DC) balances code such as Twisted Pair Ethernet(10BASE-T) during idle period, the first few bits of a message can be lost due to distortion of the bits immediately following an idle period, or by phase lock loop startup delay, and/or by related problems. Because of these bit losses, detecting and synchronizing to the beginning of a message can require the examination of several bits by receivers or repeaters. The existence of random bit errors and signals that are not messages (e.g., "heartbeat" pulses such as the Link Test Pulse (LTP) used in 10BASE-T) can increase the number of bits that must be examined to reliably detect the beginning of a message. Thus, message delays are incurred by both the time that it takes to load the elasticity buffer and the time it takes to detect and synchronize to the beginning of a message. The proposed solution is a method to minimize the sum of these two delays and to fix some of the corruptions that may have occurred to the beginning of the message.

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Elasticity Buffer Merged with Start of Message

Detection

Kevin Raymond Driscoll

ABSTRACT

Most serial communication systems contain receivers, repeaters, and transmitters,

each of which may use its own clock that is not completely synced to the other

clocks. Elasticity buffers are used to account for differences in frequency between

the transmitter's and the receiver's clocks. Further, as the transmitter's clock may be

slower than a receiver's or a repeater's, the elasticity buffer is partially filled (typically

50% filled) before the output of the buffer can start being used. In many of these

systems, and in particular those that don't maintain Direct Current (DC) balances

code such as Twisted Pair Ethernet(10BASE-T) during idle period, the first few bits

of a message can be lost due to distortion of the bits immediately following an idle

period, or by phase lock loop startup delay, and/or by related problems. Because of

these bit losses, detecting and synchronizing to the beginning of a message can

require the examination of several bits by receivers or repeaters. The existence of

random bit errors and signals that are not messages (e.g., “heartbeat” pulses such

as the Link Test Pulse (LTP) used in 10BASE-T) can increase the number of bits

that must be examined to reliably detect the beginning of a message. Thus,

message delays are incurred by both the time that it takes to load the elasticity

buffer and the time it takes to detect and synchronize to the beginning of a message.

The proposed solution is a method to minimize the sum of these two delays and to

fix some of the corruptions that may have occurred to the beginning of the message.

1. Introduction

Serial data communication is commonly used for transmission for high speed data. At

the receiver end, transmitted data has to be retrieved without losing its integrity with the

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accompanied timing information. This process is called Clock and Data Recovery

(CDR).

Figure 1- Typical processing for incoming serial data messages

Figure1 above shows the typical processing of incoming serial data messages. In order

to sample received serial data messages, the receiver (or repeater) needs to recover

incoming clock. A reference clock is aligned with the transitions in the incoming serial

data messages to recover the incoming clock. A bit stream is generated by sampling of

incoming serial data signal with the recovered clock for recovering data. Hence, the

CDR is used to recover data from incoming data stream in the absence of any

accompanying clock signal, without any bit errors due to over/under sampling.

When the repeater’s (or receiver’s) use a clock which uses a clock of different frequency

with respect to the frequency of the transmitter clock, a means to recover data

accurately includes the addition of the elasticity buffer. The elasticity buffer adds a delay

to the received data stream. Based on the added delay, a fixed total delay can be

computed. The elasticity buffer needs to be filled...