EP0827659A1

EP0827659A1 - Process for the time managing of a multiplex bus according to norm arinc 629

Info

Publication number: EP0827659A1
Application number: EP97900641A
Authority: EP
Inventors: Patrice Eudeline; Franck Gansmandel; Patrice Toillon
Original assignee: Thales Avionics SAS
Current assignee: Thales Avionics SAS
Priority date: 1996-01-19
Filing date: 1997-01-14
Publication date: 1998-03-11
Also published as: US6757252B1; FR2743966B1; FR2743966A1; WO1997026738A1

Abstract

According to the standard ARINC 629 the management process of the invention is particularly intended to the time management of an ARINC 629 bus for avionic equipments and it is characterized in that equipments which do not have new information or which have only incoherent information, are caused to emit substituted information (WS(2), WS(3)) provided with characteristic identifications (S1, S2) at the emission times which are assigned thereto (TA).

Description

PROCESS FOR THE TIME MANAGING OF A MULTIPLEX BUS ACCORDING TO NORM ARINC 629

The present invention relates to a time management method for a multiplex bus. In current aircraft, the various electromechanical and electronic devices are connected to a bus on which the information transmitted by this equipment is time multiplexed and concatenated. The management of this bus currently meets the ARINC 629 standard. This standard imposes, in particular, a time mask for the transmission times of the various devices, in order to avoid, in particular, overlapping of information of different devices.

In order to guarantee compliance with the transmission times assigned to the various items of equipment, it is known to make them systematically transmit, in turn, information on the bus. If, at the moment when they have to transmit, this equipment does not have new information, they re-transmit old information, which unnecessarily overloads the destination receivers.

The subject of the present invention is a method which makes it possible, in a system with several items of equipment connected to a time multiplex bus, to manage optimally and securely the transmissions of the items of equipment without unnecessarily overloading the receivers.

The method in accordance with the invention consists in having equipment substituted by new information, or having only inconsistent information, transmit substituted information provided with labels characteristic of the transmission times assigned to them. The present invention will be better understood on reading the detailed description of an embodiment taken by way of nonlimiting example and illustrated by the appended drawing, in which:

FIG. 1 is a diagram explaining the method of the invention in the transmission phase, and

- Figure 2 is a diagram explaining the method of the invention in reception phase.

The present invention is described below with reference to a standardized ARINC 629 bus avionics system, but it is understood that it is not limited to this application, and that it can be implemented in systems with time multiplex buses in which at at least some of the equipment attached to this bus does not have new information for each transmission cycle.

The information sent by the devices on the bus to which they are attached are grouped into word strings (WORDSTRING "in English, or WS for short in the drawing), at the rate of at least one word string per device and per occurrence d The length of a chain can be variable, without however exceeding a certain predefined maximum value so as not to disturb the sequencing of the time multiplexing. Each chain is essentially associated with two blocks in the data area corresponding to each WORDSTRING : a first block, called label, containing the various identification and management data of the chain, and a second block, informative, containing the information proper communicated by the transmitting equipment corresponding to one or more receiving equipment.

According to the invention, the information blocks transmitted on the bus only include refreshed and coherent information or alternatively substituted information preceded by a specific identification of the content ("Label" in English). Of course, the label blocks include a field R indicating the nature of this information (refreshed or not). Since these tag blocks are relatively short and can be easily processed upstream of the information processing circuits of the destination equipment, these processing circuits are not unnecessarily busy processing information which is not refreshed or not consistent. The refreshed state of an informative block is defined here as the state of this block after an update of its content by the equipment which generates it, before any transmission on the bus. Once issued, this information block is considered to be consumed, because the recipient equipment (s) will have taken it into account (whether the original information block or a substituted block due non-refresh or non-coherent access).

The consistency of an informative block, or more exactly the consistency of access to this block, is defined as the positive result of checking the actual location of this block in the area of the data to be transmitted in relation to the predefined address. of this block in the table of transmission command from the control unit attached to the transmitting equipment. The label block includes, in addition to the aforementioned field R indicating whether the corresponding informative block includes refreshed information or not, a field L making it possible to check the consistency of this informative block. Each device in the system cooperating with the ARINC bus

629 is connected to this bus via a control unit and its environment comprising, in a manner known per se, an exchange memory for transmission / reception and transmission and reception control tables making it possible to check the consistency of the chains of words issued. The switchgear with its control unit forms a unit called equipment. This control unit carries out, before the transmission of each chain of words, inter alia, the checks of refreshment of the information to be transmitted and their consistency (thanks to the consultation of said control tables and of the label block). When these checks have been carried out, it commands the transmission on the multiplex bus of the selected information (refreshed or substituted) with the corresponding identification. On reception, the control unit "filters" the incident word chains thanks to the identification received at the head of each word chain. If this identification indicates that the information block which it accompanies contains refreshed information, this is transmitted to the corresponding receiving equipment. Otherwise, the substituted information is not transmitted to this receiving device. Consequently, the apparatus only has to process updated and honest information.

We will now explain in detail the implementation of the method of the invention with reference to Figures 1 and 2 (transmission and reception, respectively).

The diagram in FIG. 1 shows, in an arbitrary conventional manner, an area 1 of data to be transmitted by any equipment A. This zone 1 comprises, for example, three data blocks (informative blocks) to be sent, respectively referenced 2, 3 and 4. To each of these blocks is associated a control structure, respectively 5, 6 and 7 (label blocks). These control structures are binary words which each contain data indicating whether the corresponding information in blocks 2 to 4 is refreshed or not, and explicitly identify the content of these blocks of information, which allows you to check their access consistency according to their content (label-address consistency mechanism). All the blocks 2 to 7 are processed by the control unit 8 relating to the apparatus considered.

In the transmission phase, when the system in which said apparatus is installed determines its instant of transmission on the multiplex bus, the control unit 8 consults the transmission control table 9. This control table includes the different addresses @ 1, @ 2, @ 3 of blocks 2 to 4 respectively. The current pointer of this table indicates among these addresses that of the block to be transmitted, and the unit 8 deduces therefrom the address of the control structure associated with the information block located at this address. The content of this control structure provides the unit 8 with the refresh state of the selected block. This content essentially comprises, as specified above, an R field and an L field.

In the simplified example of FIG. 1, block 2 comprises refreshed and consistent data as to their content (with respect to the transmission control table 9). On the other hand, block 3 has not been refreshed, and block 4 has been refreshed, but its data is inconsistent with what has been programmed in table 9. Consequently, unit 8, which must transmit an information block at the transmission time TA which is assigned to it, transmits a first chain WS (1) containing the refreshed information of block 2, a second chain WS (2) containing information substituted for that of block 3 and a third chain WS (3) also containing substituted information which are chosen from a predefined list known to all the equipment connected to the ARINC 629 bus. This list can include one or more specific substitution information, depending on the specifications of the system 629 considered. The length of the substituted block is strictly equal to that of the original block (block 3 or 4 in this example), so that from the temporal point of view no disturbance is caused for the equipment connected to the bus whatever the information that they emit. The content of the substituted block may for example include, after the identification field, a set of words identical to each other, of value equal to the length of the original block. In addition, since each piece of equipment "listens" to the bus, that is to say receives via the bus what it has just transmitted, it can control its emissions, and in particular it can control the content of the blocks substituted. On reception (FIG. 2), it is assumed that a remote device N transmits, at a time of transmission TN, four word strings (WS (W) to WS (Z)) intended for the device B, of which l control unit 8 is also shown in FIG. 2. It will be noted that the number of word strings transmitted by a given piece of equipment may be different from that of other equipment, in particular because certain pieces of equipment of an ARINC 629 system have little information to send, and others much more. The unit 8 is associated with a reception control table 10 in which are programmed the addresses of the data that it is capable of receiving, namely, in this case, @W, @X, @Y and @Z. Thus, when data passes over the bus, the control unit 8 consults the table 10 to filter it, that is to say to determine whether it is intended for it or not.

Assuming that the strings WS (W) and WS (Z) contain refreshed information, indicated by their respective identifications (labels W and Z), and the strings WS (X) and WS (Y) substitution information signaled by their specific identifications (labels S1 and S2), the unit 8 discards the data of WS (X) and WS (Y) of the zone 11 from the data to be received because they cannot be used by its equipment, which discharges the latter from the analysis of this data. On the other hand, the data of WS (W) and WS (Z) are transmitted to the area 11 of data to be received in order to be subsequently processed at addresses @W and @Z determined by the table 10. For this purpose, the unit 8 uses the control structure associated with each block of informative data (label blocks). As specified above, this control structure includes an R field with refreshed data if necessary, which is then processed by the corresponding equipment, and an L field for explicit identification of the block of informative data (consistency by content by a consistency check of the content and the address) which allows the use of the block to validate the integrity of the received block and therefore to process it later in the corresponding equipment.

Claims

1. - Time management method for a multiplex bus to which several pieces of equipment are connected, characterized in that the pieces of equipment which do not have new information, or which have only inconsistent information, transmit substituted information (WS (2), WS (3)) provided with characteristic identifications (S1, S2) at the transmission times assigned to them (TA).

2. - Method according to claim 1, characterized in that the information sent by the equipment is grouped into word strings (WS (1) to WS (3)), each of these strings comprising a block of refreshed or substituted informative data and an identification block (Label).

3. - Method according to claim 2, characterized in that the word strings containing substituted information have the same length as the strings they replace.

4. - Method according to one of the preceding claims, characterized in that on reception the substituted information is discarded by the control units (8) of the recipient equipment without being processed by them.

5. - Method according to one of the preceding claims, characterized in that it is intended for the management of an ARINC 629 type bus.