Patent Publication Number: US-9424100-B2

Title: Monitoring and validating the coordinated execution of sequenced tasks by an electronic card with two processors synchronized to different clocks

Description:
TECHNICAL FIELD 
     The present invention relates to the general field of electronic systems comprising several processors for executing functional tasks. The invention applies more particularly to an electronic system taking the form of an electronic computer onboard an aircraft. 
     In a conventional manner, with reference to  FIG. 1 , a flight computer comprises a main printed circuit card CP and two auxiliary printed circuit cards CA 1 , CA 2 . In a traditional manner, each main card CP and auxiliary card CA 1 , CA 2  comprises a processor PP 1 , PA 1 , PA 2  adapted for carrying out functional tasks defined in a program PROG communicated to the main card CP and interpreted by the processor PP 1  of the main card CR 
     The processors PP 1 , PA 1 , PA 2  of the various cards CP, CA 1 , CA 2  are linked by communication links L 1 , L 2 , for example, communication buses. By way of example, each auxiliary card CA 1 , CA 2  comprises an auxiliary processor PA 1 , PA 2  one of the functions of which consists in managing the input and output data of the computer. Hereinafter, the input/output data are designated I/O data. For example, the auxiliary processor PA 1 , PA 2  of the auxiliary card CA 1 , CA 2  reads data arising from the aircraft and dispatches orders to devices of the aircraft. The reading of data and the emission of orders are examples of functional tasks carried out by the auxiliary processor PA 1 , PA 2  of the auxiliary card CA 1 , CA 2 . 
     Stated otherwise, the main processor PP 1  of the main card CP interprets the functional tasks of the program and communicates some of them, via the communication links L 1 , L 2 , to the auxiliary processors PA 1 , PA 2  of the auxiliary cards CA 1 , CA 2  so that these latter carry out a reading of data or issue an order. 
     In a conventional manner, the functional tasks of the program PROG are sequenced and must be carried out in a determined order. To allow ordered execution of the tasks of the program PROG, the main card CP possesses a clock which makes it possible to synchronize the execution of the tasks. Instructions of the functional tasks are thereafter communicated to an auxiliary processor PA 1 , PA 2  of one of the auxiliary cards. 
     To ensure the reliability of the computer, it is necessary to have means for checking the coordination of the execution of the tasks of the main processor PP 1  with those of the auxiliary processors PA 1 , PA 2 . In practice, the clock of the auxiliary processors PA 1 , PA 2  is substantially faster than that of the main processor PP 1 , given that the auxiliary cards CA 1 , CA 2  must be highly reactive to monitor the inputs/outputs. Stated otherwise, the main processor PP 1  and the auxiliary processor PA 1  are asynchronous. 
     To allow the coordination of asynchronous processors, the prior art discloses a DMA (for “Direct Memory Access”) method between a main processor PP 1  and an auxiliary processor PA 1 , PA 2  which makes it possible to verify that the two processors PP 1 , PA 1  or PP 1 , PA 2  communicate in a coordinated manner. 
     This DMA link allows reciprocal monitoring of the asynchronous processors but remains complex to implement since it must, on the one hand, ensure that the main processor PP 1  is healthy and on the other hand, that the auxiliary processor PA 1  or PA 2  is healthy. Such synchronization means are difficult to implement and are no longer appropriate to current specifications, thereby constituting a first drawback. 
     Furthermore, having regard to the number of functional tasks to be executed by the main card CP of the computer, it has been proposed to resort to a main card CP comprising two main processors PP 1 , PP 2  which are linked together by a main communication link LP in such a way that the functional tasks are executed in a distributed manner between the two main processors PP 1  and PP 2  while making it possible to carry out several tasks in parallel. Furthermore, each main processor PP 1 , PP 2  is linked to the auxiliary processors PA 1 , PA 2  by an auxiliary communication link L 11 , L 12 , L 21 , L 22  as illustrated in  FIG. 2 . 
     Thus, for a program PROG comprising sequenced functional tasks S 1 , S 2  and S 3 , the tasks S 1  and S 3  can be carried out by the first main processor PP 1  while the task S 2  is carried out by the second main processor PP 2 . It follows that it is necessary to synchronize the operation of the two main processors PP 1 , PP 2  so as to detect in an immediate manner a possible malfunction of one of the main processors PP 1 , PP 2  or of the main communication link LP. 
     Indeed, in the absence of synchronization, the malfunction can only be observed late by a coherence checking device, thereby exhibiting a drawback. Furthermore, to coordinate the two main processors PP 1 , PP 2 , a DMA link according to the prior art cannot be implemented since it is adapted only for asynchronous operations. 
     An immediate solution for carrying out the coordination would consist in having a main processor PP 1  control the second main processor PP 2  according to the “master-slave” principle. Nonetheless, the reliability of such a solution is not satisfactory, given that a malfunction of the “master” processor would give rise directly to a malfunction of the “slave” processor. Hence, there exists a need to ensure the coordination of the tasks executed by an onboard system comprising a plurality of processors so as to monitor in a reliable manner and be able to toggle to an onboard backup system in a reactive manner in case of malfunction. 
     SUMMARY OF THE INVENTION 
     For this purpose, an aspect of the invention relates to a method for monitoring the coordinated execution of sequenced tasks by an electronic device comprising a main electronic card comprising at least one main processor synchronized to a main clock of main time period and at least one auxiliary electronic card comprising at least one auxiliary processor synchronized to an auxiliary clock of auxiliary time period, the auxiliary clock being faster than the main clock, the sequenced tasks having to be carried out simultaneously by the processors, in which method:
         over a determined main time period, the main processor executes a first sequenced task while the auxiliary processor executes instructions of the first sequenced task over a plurality of auxiliary time periods;   over the consecutive main time period, the main processor executes a second sequenced task;       

     the method comprising:
         a step of emission by the main processor of a coordination marker to the auxiliary processor at the start of each main time period;   a step of emission by the auxiliary processor of a response word formed on the basis of the last coordination marker received to the main processor at the end of each auxiliary time period;   a step of validation by the main processor of the response word received with respect to the first coordination marker emitted, the validation step being carried out at the start of the consecutive time period before the emission of a new coordination marker; and   a step of signaling by the main processor if the response word received is not valid so as to signal a defect of coordination of the auxiliary processor.       

     The method advantageously allows the main processor to monitor the auxiliary processor in a simple and reactive manner, the coordination markers being dispatched systematically and in a regular manner. This is particularly advantageous for two asynchronous processors belonging to different cards. As the monitoring is carried out only by the main processor, the detection of a malfunction is very reactive (for example less than 10 ms), the main processor being monitored by other means. The monitoring method is easy to implement, thereby facilitating its installation and its application to a plurality of different cards. 
     Preferably, the signaling step comprises a step of emitting an alarm. 
     Preferably, the auxiliary card and the main card are linked by at least one auxiliary communication link. During the monitoring, any defect of the communication link is manifested by a delay or a deformation of the coordination markers and results in an emission of an alarm. Stated otherwise, the monitoring method is reliable and covers any malfunction of the electronic device. 
     Preferably still, the nature of the coordination marker is defined as a function of the topology of the auxiliary communication link so as to allow a highlighting of a current defect of said auxiliary communication link, preferably, a sticking of two consecutive bits of said auxiliary communication link. 
     Thus, for a communication link taking the form of a communication bus comprising 8 wires, the coordination marker is a hexadecimal integer coded on 32 bits. 
     Preferably, the coordination markers are dispatched in an alternate manner so as to distinguish two main time periods. Preferably still, the dispatched coordination markers are two in number. 
     According to one aspect of the invention, the response word is the complement of the last coordination marker received. Such a response word is, on the one hand, simple for the auxiliary processor to form and, on the other hand, simple for the main processor to compare. This is particularly advantageous for the auxiliary processor which has an auxiliary time period of short duration in which to form the response word. 
     Preferably, the main processor keeps only the last response word received so as to accelerate the monitoring method. 
     According to a preferred aspect, the electronic device comprising two auxiliary electronic cards comprising at least one auxiliary processor synchronized to an auxiliary clock of auxiliary time period, the main processor monitors the coordination of the execution of sequenced tasks on each auxiliary processor. Thus, the number of auxiliary cards can be increased without affecting the reliability of the monitoring. 
     According to another preferred aspect, the main electronic card comprising at least two main processors synchronized to one and the same main clock of main time period, each main processor monitors the coordination of the execution of sequenced tasks on the auxiliary processor. Thus, each auxiliary processor is monitored in two independent ways, the main processors being able to monitor one another reciprocally. 
     The invention relates furthermore to a method for monitoring the coordinated execution of sequenced tasks by an electronic card comprising at least one first processor and one second processor synchronized to one and the same clock of determined time period, the execution of the sequenced tasks being distributed between the processors, in which method:
         over a determined time period, the first processor executes a first sequenced task while the second processor executes a first accessory task;   over the consecutive time period, the second processor executes a second sequenced task subsequent to the first sequenced task;       

     the method comprising:
         a step of recording in memory means by the first processor of a first identifier characterizing the time period in the course of which the first sequenced task has been executed, the recording step being carried out in the course of the determined time period after execution of the first sequenced task;   a step of recording in the memory means by the second processor of a second identifier characterizing the time period in the course of which the first accessory task has been executed, the recording step being carried out in the course of the determined time period after execution of the first accessory task;   a step of comparison by the first processor of the first identifier and of the second identifier recorded in the memory means, the comparison step being carried out in the course of the consecutive time period; and   a step of signaling by the first processor in the case of failure of the comparison so as to signal a defect of coordination of the processors.       

     By virtue of the monitoring method according to an aspect of the invention, the first processor can guarantee that the second processor executes the sequenced task in a coordinated manner over the determined time period. Thus, the sequenced tasks can be executed one after another in an optimal manner without risk of error. In an advantageous manner, the monitoring method makes it possible to detect a large number of malfunctions related to the processors and/or to the memory means. Moreover, this detection is reactive since a malfunction is detected in the time period in which it arises, this being advantageous by comparison with the prior art. This reactivity makes it possible during the signaling to transfer the functional tasks to a backup electronic card which deputizes for the failed electronic card and thus guarantee the reliability of the execution of the functional tasks. 
     Preferably, the first processor executing a second accessory task over the consecutive time period, the comparison step is carried out in the course of the consecutive time period before the execution of the second accessory task. Thus, it is determined in a reactive manner at the start of the consecutive time period whether a defect of coordination has occurred, this being advantageous. 
     According to one aspect of the invention, the accessory tasks (that is to say tasks that are not necessarily sequenced) can be mute tasks and not comprise any instructions. Stated otherwise, such accessory tasks correspond to rest periods of the processor. 
     Preferably, the consecutive time period is the time period which directly follows the determined time period but it goes without saying that the consecutive time period could be several clock cycles distant temporally from the determined time period. 
     Preferably, the method comprises a step of comparison by the second processor of the first identifier and of the second identifier recorded in the memory means, the comparison step being carried out in the course of the consecutive time period before the execution of the second sequenced task and a step of signaling by the second processor if the identifiers are not equal so as to signal a defect of coordination of the processors. 
     Advantageously, the second processor can guarantee that the first processor executes the sequenced task at the right moment, in tune with the synchronization of the processors. Stated otherwise, the processors monitor one another in a reciprocal manner, thereby improving the reliability of the execution of the functional tasks. 
     Preferably, the recording steps are implemented directly after the execution of the first accessory task and of the first sequenced task. Thus, the processors execute the recording instructions directly after having executed the instructions of the functional tasks so that the memory means comprise the most recent information. 
     Preferably still, the steps of the monitoring method are implemented at each time period. Thus, the electronic card is monitored in real time in the course of time, for example, throughout the duration of flight of an aircraft comprising said electronic card. 
     Preferably, the identifiers are integer numbers so as to distinguish the consecutive time periods. 
     According to a preferred aspect of the invention, the memory means take the form of a RAM memory linked to the two processors. Such a RAM memory is simple to implement on an electronic card and makes it possible to serve as intermediary, given that the recording steps can occur at different instants. 
     Preferably, each processor is linked to the RAM memory by a communication link. During the monitoring, any defect of the communication link is manifested by a delay or a deformation of the identifiers and results in a signaling, for example, an emission of an alarm. Stated otherwise, the monitoring method is reliable and covers any malfunction of the electronic card. 
     According to embodiments of the invention, the memory means belong to at least one of the processors or are independent of the processors. 
     Preferably, the electronic card being a main electronic card of an electronic device comprising at least two main processors synchronized to a main clock of determined main time period, the electronic device furthermore comprising at least one auxiliary electronic card comprising at least one auxiliary processor synchronized to an auxiliary clock of determined auxiliary time period, the auxiliary clock being faster than the main clock, sequenced tasks having to be carried out simultaneously by one of the main processors and the auxiliary processor, in which method:
         over a determined main time period, the first main processor executes a first sequenced task while the auxiliary processor executes instructions of the first sequenced task over a plurality of auxiliary time periods;   over the consecutive main time period, the first main processor executes a second sequenced task;       

     the method comprising:
         a step of emission by the first main processor of a coordination marker to the auxiliary processor at the start of each main time period;   a step of emission by the auxiliary processor of a response word formed on the basis of the last coordination marker received to the first main processor at the end of each auxiliary time period;   a step of validation by the first main processor of the response word received with respect to the first coordination marker emitted, the validation step being carried out at the start of the consecutive main time period before the emission of a new coordination marker; and   a step of signaling by the first main processor if the response word received is not valid so as to signal a defect of coordination of the auxiliary processor.       

     In an advantageous manner, each main processor monitors the auxiliary processor, thereby guaranteeing great reliability of the method. Furthermore, as the main processors monitor one another in a reciprocal manner, a complete and redundant monitoring method is afforded which allows reactive (for example less than 10 ms) and systematic detection of any malfunction. The monitoring method is easy to implement, thereby facilitating its installation and its application to a plurality of different cards. 
     Preferably, the electronic device comprising at least two auxiliary electronic cards, each main processor of the main electronic card monitors the coordination of the execution of the sequenced tasks by each of the auxiliary processors. Such a monitoring method is advantageously generalizable to several auxiliary cards while guaranteeing the same level of reliability and the same level of complexity. 
     The invention is particularly advantageous for the monitoring of an electronic device of the onboard computer type, aboard an aircraft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the description which follows, given solely by way of example, and referring to the appended drawings in which: 
         FIG. 1  is a schematic representation of a computer according to the prior art with a main card comprising only a single main processor; 
         FIG. 2  is a schematic representation of a computer according to the prior art with a main card comprising two main processors; 
         FIG. 3  is a schematic representation of a computer according to an embodiment of the invention with a main card comprising two main processors; 
         FIG. 4  is a schematic chart of a method for coordinating the two main processors of  FIG. 3 ; 
         FIG. 5A  is a first exemplary implementation of the coordination of the two synchronized main processors according to an aspect of the invention; 
         FIG. 5B  represents the state of the RAM memory during the implementation of the first example of  FIG. 5A ; 
         FIG. 6A  is a second exemplary implementation of the coordination of the two synchronized main processors during a defect of coordination according to an aspect of the invention; 
         FIG. 6B  represents the state of the RAM memory during the implementation of the second example of  FIG. 6A ; 
         FIG. 7  is a schematic chart of a method for coordinating a main processor with an auxiliary processor; 
         FIG. 8  is a first exemplary implementation of the coordination of a main processor with an auxiliary processor according to an aspect of the invention; 
         FIG. 9  is a second exemplary implementation of the coordination of a main processor with an auxiliary processor during a defect of coordination according to an aspect of the invention; and 
         FIG. 10  is a schematic representation of a computer, according to an embodiment of the invention, on which the monitoring methods implemented are indicated. 
     
    
    
     It should be noted that the figures set forth the invention in detail so as to implement the invention, said figures being able of course to serve to better define the invention if appropriate. 
     DETAILED DESCRIPTION 
     An embodiment of the invention will be presented for an electronic device which takes the form of an onboard electronic computer aboard an aircraft. It goes without saying that the invention applies to any type of electronic device comprising a plurality of computation processors such as for example an electronic device for use in the railroad sector, mobile telephony, the space or automobile sector. 
     In this example, the computer comprises a main printed circuit card CP and two auxiliary printed circuit cards CA 1 , CA 2  as illustrated in  FIG. 3 . To have significant computation power, the main card CP comprises two main processors PP 1 , PP 2  so as to carry out functional tasks in parallel. As will be presented in detail subsequently, the main processors PP 1 , PP 2  are linked by a communication link so as to allow the exchange of data between the processors PP 1 , PP 2 . 
     For its part, each auxiliary card CA 1 , CA 2  comprises an auxiliary processor PA 1 , PA 2  for processing functional tasks provided by the main processors PP 1 , PP 2 . For this purpose, each auxiliary processor PA 1 , PA 2  is linked by an auxiliary communication link L 11 , L 12 , L 21 , L 22  to each of the main processors PP 1 , PP 2  as illustrated in  FIG. 3 . Preferably, the communication links L 11 , L 12 , L 21 , L 22  take the form of communication buses comprising 8 wires for the communication of data coded on 32 bits. 
     In this exemplary embodiment, the auxiliary processors PA 1 , PA 2  of the auxiliary cards CA 1 , CA 2  are adapted for managing the input and output data of the flight computer. Hereinafter, the input/output data are designated I/O data. For example, the processor PA 1 , PA 2  of the auxiliary card CA 1 , CA 2  reads the data arising from the aircraft and issues orders to devices of the aircraft. 
     These functional tasks are defined in a software program PROG which is provided to the flight computer and interpreted by the main processors PP 1 , PP 2  of the main card CP. To increase the computation power and to load the various main processors PP 1 , PP 2  equitably, the functional tasks are distributed between the two main processors PP 1 , PP 2  for their execution by the main electronic card CP. These functional tasks comprise a set of instructions a part of which can be entrusted to one or more auxiliary processors PA 1 , PA 2  for their execution. The instructions arising from a functional task which are processed by an auxiliary processor PA 1 , PA 2  are subsequently designated functional instructions. 
     The main processors PP 1 , PP 2  are synchronized to one and the same main clock H of time period T so as to allow optimal chaining of the execution of the functional tasks. By way of example, the time period T of the main clock H is 5 ms. 
     Each auxiliary processor PA 1 , PA 2  is synchronized to an auxiliary clock H 1 , H 2  of time period t which is faster than the main clock H. By way of example, the time period t of each auxiliary clock H 1 , H 2  is 500 μs. Stated otherwise, each auxiliary processor PA 1 , PA 2  runs 10 times as quickly as a main processor PP 1 , PP 2 , the main processors PP 1 , PP 2  and auxiliary processors PA 1 , PA 2  being asynchronous. 
     According to an aspect of the invention, the monitoring of the coordination of the various processors PP 1 , PP 2 , PA 1 , PA 2  is carried out by:
         a first monitoring method  10  ( FIG. 4 ) dedicated to the monitoring of synchronous processors and   a second monitoring method  20  ( FIG. 7 ) dedicated to the monitoring of synchronous/asynchronous processors.       

     According to an aspect of the invention, the software program PROG comprises functional tasks S 1 -S 4  which are sequenced, that is to say, that they must be executed according to an ascending order relation. Indeed, the functional task S 3  can comprise parameters which must be computed in the course of the functional task S 2 . 
     As illustrated in  FIG. 3 , the main electronic card CP comprises memory means which take, preferably, the form of a RAM memory  4  linked to the two main processors PP 1 , PP 2 , but it goes without saying that the memory means can take diverse forms, for example, the form of a memory internal to a main processor PP 1 , PP 2 , shared between the two main processors PP 1 , PP 2  or a memory external to the main electronic card CP. Furthermore, the memory means  4  can take the form of a unit memory block or the form of a plurality of memory modules that are connected or independent of one another. 
     Still with reference to  FIG. 3 , in this embodiment of the invention, the first main processor PP 1  is linked to the RAM memory  4  by a first main link LP 1  while the second main processor PP 2  is linked to the RAM memory  4  by a second main link LP 2 . In this example the main links LP 1 , LP 2  take the form of communication buses comprising 8 wires for the communication of data coded on 32 bits. 
     In the example which follows, the functional program comprises four sequenced functional tasks S 1 -S 4  which must be executed by the first main processor PP 1  with the exception of the functional task S 2  which must be executed by the second main processor PP 2 . The functional tasks S 1 -S 4  must be respectively executed over the time periods T 1 -T 4 . 
     When a main processor PP 1 , PP 2  is not occupied by the execution of one of the sequenced functional tasks S 1 -S 4 , it executes accessory tasks (or background tasks) N 1 , N 2 , Q 1 , R 1  as illustrated in  FIG. 5A . These accessory tasks can consist, for example, in the execution of cyclic tasks or functional tasks which do not have any sequencing constraint. 
     The accessory tasks can be mute tasks and not comprise any instructions. According to the latter assumption, such accessory tasks correspond to rest periods of the processor. 
     First Monitoring Method  10   
     By virtue of the first monitoring method  10  according to an aspect of the invention, the coordination of the execution of the sequenced functional tasks S 1 -S 4  by the main processors PP 1 , PP 2  is ensured. 
     With reference to  FIG. 5A , over the determined time period T 1 , the first main processor PP 1  executes a first sequenced task S 1  while the second processor PP 2  executes a first accessory task N 1 . Over the consecutive time period T 2 , the first main processor PP 1  executes a second accessory task N 2  while the second main processor PP 2  executes a second sequenced task S 2  subsequent to the first sequenced task S 1 . 
     According to an aspect of the invention, with reference to  FIG. 4 , the method comprises a step of recording  11  in the RAM memory  4  by the first main processor PP 1  of a first identifier ID 1  characterizing the time period T 1  in the course of which the first sequenced task S 1  has been executed. In this example, the first identifier ID 1  corresponds to the reference of the time period concerned (ID 1 =T 1 ). It goes without saying that the identifier could correspond to any information relating to the time period concerned (name of time period, relative or absolute reference, etc.). 
     As illustrated in  FIG. 5A , the recording step  11  is carried out in the course of the determined time period T 1 , after execution of the first sequenced task S 1 . In this example this recording step  11  takes the form of a step of writing by the first main processor PP 1  to the RAM memory  4 . In this example, with reference to  FIG. 5B , the RAM memory  4  comprises a memory space dedicated to the first identifier ID 1  to which the first main processor PP 1  writes, via the first main communication link LP 1 . 
     In a similar manner, with reference to  FIG. 4 , the method comprises a step of recording  12  in the RAM memory  4  by the second main processor PP 2  of a second identifier ID 2  characterizing the time period T 1  in the course of which the first accessory task N 1  has been executed. As illustrated in  FIG. 5A , the recording step  12  is carried out in the course of the determined time period T 1  after execution of the first accessory task N 1 . In a similar manner, the second identifier ID 2  corresponds to the reference of the time period concerned (ID 2 =T 1 ). 
     In this example this recording step  12  takes the form of a step of writing by the second main processor PP 2  to the RAM memory  4 . In a similar manner, with reference to  FIG. 5B , the RAM memory  4  comprises a memory space dedicated to the second identifier ID 2  to which the second main processor PP 2  writes, via the second main communication link LP 2 . 
     Preferably, the identifiers ID 1 , ID 2  are integers coded on 32 bits and take values lying between 1 and 24, this being sufficient to ensure the differentiation of two consecutive time periods T 1 , T 2 . Nonetheless, it goes without saying that the identifiers ID 1 , ID 2  could take different values. 
     The instants of execution of the recording steps  11 ,  12  depend on the duration of execution of the functional task over the time period concerned. Thus, with reference to  FIG. 5A , the step of writing  12  over the time period T 1  is earlier than the step of writing  11  over the time period T 2 . 
     Still with reference to  FIG. 4 , the method comprises a step of comparison  13  by the first main processor PP 1  of the first identifier ID 1  and of the second identifier ID 2  recorded in the RAM memory  4 . The comparison step  13  is carried out in the course of the consecutive time period T 2  before the execution of the second accessory task N 2  by the first main processor PP 1  so as to avoid any time offset between the two main processors PP 1 , PP 2 . 
     Furthermore, the second accessory task N 2  starts only when the comparison step  13  has terminated so as to take account of the communication lags between the first main processor PP 1  and the RAM memory  4 . 
     With reference to  FIGS. 5A and 5B , during the comparison step  13 , the memory spaces dedicated to the identifiers ID 1 , ID 2  of the RAM memory  4  are read by the first main processor PP 1  and then inter-compared. If the identifiers ID 1 , ID 2  are not equal, the method comprises a signaling step  15 , preferably, an emission of an alarm ALARM by the first main processor PP 1  to signal a defect of coordination of the main processors PP 1 , PP 2 . Still with reference to  FIGS. 5A and 5B , as the identifiers ID 1 , ID 2  both equal T 1 , no alarm is emitted. 
     With reference to  FIG. 4 , the method comprises a step of comparison  14  by the second main processor PP 2  of the first identifier ID 1  and of the second identifier ID 2  recorded in the memory means  4 . In a similar manner, the comparison step  14  is carried out in the course of the consecutive time period T 2  before the execution of the second sequenced task S 2  by the second main processor PP 2  and an alarm is emitted  15  by the second main processor PP 2  to signal a defect of coordination of the main processors PP 1 , PP 2  if the identifiers ID 1 , ID 2  are not equal. 
     If no defect of coordination has occurred, new recording steps  11 ,  12  arise subsequent to the execution of the functional tasks N 2 , S 2  by the main processors PP 1 , PP 2  as illustrated in  FIG. 5A . For a mute accessory task, that is to say, divested of instructions, the recording step is directly carried out subsequent to the comparison step. 
     The example of  FIGS. 5A and 5B  illustrates a coordinated execution of the sequenced functional tasks S 1 -S 4 , the comparison steps  13 ,  14  verifying that the main processors PP 1 , PP 2  execute their tasks in the course of the same temporal instant T 1 -T 4 . For this purpose, no alarm is emitted. 
     The example of  FIGS. 6A and 6B  illustrates an execution of the sequenced functional tasks S 1 -S 4  over the time periods T 1 -T 4  in the course of which a malfunction arises. In this example, the second main processor PP 2  executes the first accessory task N 1  in the course of the first time period T 1  and records its second indicator ID 2 =T 1  in the RAM memory  4  (recording step  12 ). Thereafter, the second main processor PP 2  executes the second sequenced task S 2  in the course of the second time period T 2 . On account of a malfunction, the duration of the time period T 2  is elongated as illustrated in  FIG. 6A . It follows from this that the first main processor PP 1  executes its second accessory task N 2  in a faster manner than the second sequenced task S 2 . 
     At the end of the accessory task N 2 , the first main processor PP 1  writes the first identifier ID 1 =T 2  to the RAM memory  4  (recording step  11 ). At the start of the third time period T 3 , before the execution of the third sequenced task S 3  by the first main processor PP 1 , the first main processor PP 1  compares the first identifier ID 1  and the second identifier ID 2  recorded in the RAM memory  4  (comparison step  13 ). With reference to  FIG. 6B , the first identifier ID 1  of value T 2  and the second identifier ID 2  of value T 1  are not equal. It follows from this that an alarm is emitted immediately by the main processor PP 1  to signify a defect of coordination. Thus, the alarm is emitted right from the first time period T 1 , thereby guaranteeing reactive monitoring. In an advantageous manner, it is possible to toggle to a backup electronic device even before a defect of control is observed. 
     The alarm can take diverse forms, for example, a visual or sound signal, an emergency command, a control to toggle to another onboard device, etc. 
     Thus, in an advantageous manner, the first main processor PP 1  and the second main processor PP 2  monitor one another in a reciprocal manner to detect any temporal desynchronization of the processors PP 1 , PP 2 , any defect of coordination of the execution of the functional tasks, any defect of alertness of the main processors (shutdown of the processor, shutdown of the execution of the functional task). Furthermore, any defect of the main communication pathways LP 1 , LP 2  between the main processors PP 1 , PP 2  or of the RAM memory  4  is immediately detected, this also being advantageous. 
     Second Monitoring Method  20   
     As indicated previously, the software program PROG comprises functional tasks S 1 -S 4  which are sequenced, that is to say, that they must be executed according to an ascending order relation. 
     When a functional task S 1 -S 4  is carried out by one of the main processors PP 1 , PP 2 , the main processor concerned can subcontract instructions of the functional task concerned to an auxiliary processor PA 1 , PA 2 . To improve processing reactivity, the auxiliary processors PA 1 , PA 2  and the main processors PP 1 , PP 2  are asynchronous. 
     By virtue of the monitoring method, which will be presented subsequently, according to an aspect of the invention, the coordination of the execution of the sequenced functional tasks S 1 -S 4  is ensured between a main processor PP 1 , PP 2  and an auxiliary processor PA 1 , PA 2 . 
     By way of example, with reference to  FIGS. 7 to 9 , the monitoring of the coordination between the first main processor PP 1  and the first auxiliary processor PA 1  will be presented for the processing of the sequenced functional tasks S 1 , N 2 . Each functional task S 1 , N 2  comprises respectively functional instructions s 1 , n 2  which must be executed in a manner that is coordinated by the first auxiliary processor PA 1 . 
     As the main processors PP 1 , PP 2  and the auxiliary processors PA 1 , PA 2  are not synchronous, the first monitoring method  10  presented previously with reference to  FIG. 4  cannot be implemented. 
     With reference to  FIG. 8 , over the determined time period T 1  of duration 5 ms, the first main processor PP 1  executes a first sequenced task S 1  while the first auxiliary processor PA 1  executes first functional instructions s 1  over about ten auxiliary time periods t 1 -t 10  of individual duration 500 μs. 
     Over the consecutive time period T 2 , the first main processor PP 1  executes a second accessory task N 2  while the first auxiliary processor PA 1  executes second accessory instructions n 2  over about ten temporal durations t 11 -t 20 . 
     According to an aspect of the invention, with reference to  FIGS. 7 and 8 , the method comprises a step of emission  21  by the first main processor PP 1  of a coordination marker M A , M B  to the first auxiliary processor PA 1  at the start of each main time period T 1 -T 2 . In this example, the first main processor PP 1  emits a first coordination marker M A  via the auxiliary communication line L 11  to the first auxiliary processor PA 1  at the start of the main time period T 1 . 
     Subsequent to the emission of the first coordination marker M A , the method comprises a step of emission  22  by the first auxiliary processor PA 1  of a response word ACK formed on the basis of the last coordination marker received M A . The response word ACK is dispatched to the first main processor PP 1  at the end of each auxiliary time period t 1 -t 10 . Thus, as illustrated in  FIG. 8 , in the course of the main time period T 1 , ten response words ACK are dispatched by the first auxiliary processor PA 1 . 
     Preferably, the response word ACK is the complement of the last coordination marker received M A  received. Stated otherwise, the response word ACK is equal to  M A     as illustrated in  FIG. 8 . 
     Preferably, the main processor PP 1  keeps only the last response word ACK received. Stated otherwise, the last response word ACK received overwrites the response word received previously. 
     Subsequent to the emission of the response word ACK, the method comprises a step of validation  23  by the first main processor PP 1  of the response word ACK received with respect to the first coordination marker M A  emitted, the validation step  23  being carried out at the start of the consecutive time period T 2  before the emission of a new coordination marker M B . Thus, the first main processor PP 1  checks the coherence of the response word received ACK so as to ensure that the communication link L 11  and the first auxiliary processor PA 1  have not failed and do not “deform” the coordination marker M A  initially dispatched by the first main processor PP 1 . 
     Finally, the method comprises a signaling step  24 , preferably, an emission of an alarm by the first main processor PP 1  if the response word received ACK is not valid so as to signify a defect of coordination between the first main processor PP 1  and the first auxiliary processor PA 1 . 
     In this example, with reference to  FIG. 8 , at the start of the consecutive time period T 2 , the first main processor PP 1  verifies that the response word received ACK is indeed the complement of the first coordination marker M A  initially dispatched. As this is the case in the example of  FIG. 8 , no alarm is emitted. Hence, a new coordination marker M B  is dispatched by the first main processor PP 1  at the start of the second time period T 2  and a plurality of response words ACK ( M B   ) are dispatched by the first auxiliary processor PA 1 . By ensuring that the coordination markers M A , M B  are properly received, the first main processor PP 1  can verify the integrity of the first auxiliary processor PA 1  as well as the integrity of the auxiliary communication link L 11 . 
     In this example, each auxiliary communication link L 11 , L 12 , L 21 , L 22  takes the form of a BUS link with 8 wires for the communication of data coded on 32 bits. 
     Preferably, the coordination markers M A , M B  are two in number and are emitted in an alternate manner at the start of the main time periods T 1 , T 2 . The intrinsic nature of the coordination markers M A , M B  is defined so as to make it possible to detect a defect of transmission of bits of the coordination markers M A , M B . Furthermore, the two coordination markers M A , M B  are defined with respect to one another so as to favor identification of transmission defect. Preferably, the coordination markers M A  and M B  are defined so as to allow the detection of a determined defect, for example, the sticking of two consecutive bits. 
     Such coordination markers M A , M B  are related to the communication bus topology and make it possible to verify with relevance any defect of the stuck bits type for each auxiliary communication link L 11 , L 12 , L 21 , L 22 . Preferably, the method implements more than two different coordination markers so as to allow precise and fast verification of the set of wires of the auxiliary communication links L 11 , L 12 , L 21 , L 22 . 
     In an advantageous manner, the second monitoring method  20  is flexible to implement since it does not seek to measure that the set of response words ACK has indeed been received by the first main processor PP 1  but solely that the tasks which are executed are properly coordinated. For this purpose, it is necessary for the auxiliary time period t 1 -t 20  to be shorter than a main time period T 1 . 
     With reference now to the example of  FIG. 9 , the first auxiliary processor PA 1  experiences a malfunction which prevents it from receiving the second coordination marker M B  at the start of the second main time period T 2 . It follows from this that the first auxiliary processor PA 1  continues to emit the complement of the first coordination marker  M A     as response word ACK instead of emitting the complement of the first coordination marker  M B   . 
     Thus, during the comparison step  23  at the start of the third main time period T 3 , the first main processor PP 1  compares the last coordination marker dispatched M B  and the last response word  M A     received. As the response word  M A     is not the complement of the last coordination marker dispatched M B , the method emits an alarm to signify a defect of coordination. 
     Thus, the alarm is emitted right from the start of the third time period T 3 , thereby guaranteeing reactive monitoring. In an advantageous manner, it is possible to toggle to a backup electronic device even before a defect of control is observed. 
     Thus, in an advantageous manner, the first main processor PP 1  monitors the first auxiliary processor PA 1  as well as the communication link L 11  linking the first main processor PP 1  to the first auxiliary processor PA 1  so as to detect any defect of temporal coordination of the processors PP 1 , PA 1 , any defect of coordination of the execution of the functional tasks, any defect of alertness of the processors (shutdown of the processor, shutdown of the execution of the functional task). Thus, the processor having the longest time period can monitor the processor having the shortest time period. 
     Preferably, the second monitoring method  20  comprises a preliminary initialization phase in the course of which the main processor PP 1  emits an initialization marker and receives the complemented marker in response. 
     Global Monitoring of the Device 
     In an advantageous manner, the device considered as a whole with its main electronic card CP and its auxiliary cards CA 1 , CA 2  is monitored in a precise and reactive manner by the monitoring methods detailed previously. 
     Thus, by virtue of the second monitoring method  20 , each auxiliary processor PA 1 , PA 2  is monitored by each of the main processors PP 1 , PP 2 , thereby improving the reliability of the monitoring for the coordination of the execution of functional tasks on asynchronous or synchronized processors. The second monitoring method  20  furthermore guarantees the integrity of the auxiliary communication links L 11 , L 12 , L 21 , L 22  between each main processor PP 1 , PP 2  and each auxiliary processor PA 1 , PA 2 . 
     The second monitoring method allows the processor having the longest time period (main processor) to monitor the processor having the shortest time period (auxiliary processor). This does not present any drawbacks in the present invention having regard to the fact that the main processors PP 1 , PP 2  mutually monitor one another. Hence, each of the processors is at least monitored by another processor, thereby guaranteeing reliability of the monitoring of the computer. 
     Incidentally, the second monitoring method  20  is also applicable for coordinating two synchronized processors. According to this assumption, just one response word is transmitted per clock cycle. 
     The first monitoring method  10  makes it possible to ensure reciprocal monitoring of the coordination of the main processors PP 1 , PP 2  which are synchronized, as well as the integrity of the main communication links LP 1 , LP 2 . 
     Thus, the set of processors can be fully monitored for a card comprising at least three diverse processors or at least two synchronized processors, thereby conferring significant reliability on the electronic card. 
     The first monitoring method  10  is particularly adapted for monitoring a serial pathway comprising two communication wires which extends between two processors so as to detect a cutoff or stuck bits. The second monitoring method  20  is particularly adapted for monitoring the integrity of a parallel communication pathway comprising more than two communication wires. 
     To monitor the integrity of the computations of the processors, the two monitoring methods  10 ,  20  carry out in an advantageous manner a comparison step which is direct for the first monitoring method  10  or indirect for the second monitoring method  20  because of the computation of the response word (complement). 
     On account of the implementation of monitoring methods  10 ,  20 , on the one hand, for synchronized processors and, on the other hand, for asynchronous processors, the computer is monitored in an optimal manner. 
     It goes without saying that the invention relates to a main card CP which comprises more than two main processors as well as auxiliary cards which comprise more than one auxiliary processor. Indeed, the two methods make it possible to solve on the one hand the coordination between synchronized processors, and also the coordination between unsynchronized processors. The coordination methods are therefore generalizable to a card comprising any number of main processors and any number of auxiliary processors.