Method for synchronizing clocks in a distributed communication system

Abstract

The invention refers to one of a number of nodes of a communication system. The nodes are connected to a communication media for transmitting data among the nodes. Said one node comprises a communication controller, across which the node is connected to the communication media, and a bus guardian for controlling access of the communication controller to the communication media. In order to provide a cheap but nevertheless reliable way for monitoring the synchronized clock signal of a node of a communication system and in particular for detecting deviations of the synchronized clock signal it is suggested that a synchronized clock signal from the communication controller is made available to the bus guardian, and that the bus guardian comprises means for monitoring the synchronized clock signal using a bus guardian internal clock signal, which is generated by means of an electronic circuit and which is less accurate than the synchronized clock signal to be monitored.

Description

[0001] This application is a continuation of PCT / EP03 / 03992 filed on Apr. 16, 2003 and also claims Paris Convention priority of EP 02 008 171.7 and DE 102 16 984.5 both filed on Apr. 16, 2002, the entire disclosures of which are all hereby incorporated by reference.BACKGROUND OF THE INVENTION [0002] The present invention refers to one of a number of nodes of a communication system. The nodes are connected to a communication media for transmitting data among the nodes. Said one node comprises a communication controller, across which the node is connected to the communication media, and a bus guardian for controlling access of the communication controller to the communication media. [0003] Furthermore, the invention refers to a method for monitoring a synchronized clock signal from a communication controller of a node making part of a number of nodes of a communication system. The nodes are connected to a communication media for transmitting data among the nodes. Said node comprises a...

AI Technical Summary

Benefits of technology

[0015] According to the present invention it is suggested to effect a clock signal monitoring using an internal clock signal having a lower accuracy than the clock signal to be monitored. Of course, according to the present invention only a coarse monitoring of the synchronized clock signal can be achieved. But the achievable accuracy is accurate enough in order to determine larger deviations of the monitored clock signal from a nominal signal and is for example + / −50%. Large deviations may be caused by a crystal that is oscillating at a different harmonic or a frequency divider inside the communication controller that is operating at an incorrect ratio. These defects of the communication controller can be reliably detected with the present invention.

[0016] The bus guardian comprises an electronic circuit for monitoring the received synchronized clock signal. This has the advantage that the bus guardian does not need its own oscillator for generating a reference signal and for monitoring the synchronized clock signal. Other than an oscillator which serves for creating a reference signal with as high a precision as possible, the electronic circuit is much simpler and cheaper and serves for roughly monitoring the macroticks received from the communication controller.

[0030] According to another preferred embodiment of the present invention it is suggested that the means for monitoring the additional clock signal count the number of internal clock signal periods (local clock periods) during multiple additional clock signal periods (bus guardian tick periods). Preferably, the means for monitoring the synchronized clock signal count the number of additional clock signal periods (bus guardian tick periods) during multiple synchronized clock signal periods. By counting the number of local clock periods or bus guardian tick periods respectively over multiple periods of the bus guardian tick or the synchronized clock signal respectively, the precision of the monitoring can be improved.

Problems solved by technology

However, the use of oscillators for generating the signals used for monitoring the clock signal in a bus guardian of a node in a communication system is inefficient and expensive.

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