Abstract:
An information processing device having two processing units capable of operating in synchronization with each other, includes: a common unit capable of outputting an identical signal to the two processing units; detection units that are respectively provided for the processing units and each detects errors occurred in corresponding processing unit respectively; a comparison unit that compares outputs from the two processing units; and a control unit that controls signals from the processing units to the common unit, based on a detection result of the detection units and a comparison result of the comparison unit, and determines, if errors of an identical type are simultaneously detected by the detection units, that the errors are due to an error of the common unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application, filed under 35 U.S.C. §111(a), of PCT Application No. PCT/JP2007/056858, filed Mar. 29, 2007, the disclosure of which is herein incorporated in its entirety by reference. 
     
    
     FIELD 
       [0002]    The embodiments discussed herein are related to an information processing device having plural processing devices synchronized with each other, and an error, processing method. 
       BACKGROUND 
       [0003]    An information processing system using a conventional mirror mode (duplexing) will now be described. The mirror mode is an information processing technique of allowing a system to operate, even when a trouble occurs on one system, with use of another line by performing processing while synchronizing the one line (synchronized unit) with the another line. 
         [0004]    Now, a description will be made of a system configuration of a conventional information processing system using a mirror mode.  FIG. 25  is a block diagram illustrating a configuration example of a conventional information processing system. The information processing system is constituted by two lines A and B which perform synchronous operation, and includes a control system  1 , processing devices  2   a   0  and  2   a   1  on the line A, and processing devices  2   b   0  and  2   b   1  on the line B. The processing devices are, for example, CPUs. The processing devices  2   a   0 ,  2   a   1 ,  2   b   0 , and  2   b   1  each has an error checker inside. The control system  1  includes an interface (A IF)  4   a  for the line A, an interface (B IF)  4   b  for the line B, error checkers  7   a  and  7   b,  a comparator  9 , a selector generation unit  12 , a selector  14 , and a common unit  15 . Of these components, the processing devices  2   a   0 ,  2   a   1 , A IF  4   a,  and error checker  7   a  are on the line A while the processing devices  2   b   0 ,  2   b   1 , B IF  4   b,  and error checker  7   b  are on the line B. 
         [0005]    The control system  1  is connected to the processing devices  2   a   0  and  2   a   1  through a route  3   a  and the A IF  4   a,  and is also connected to the processing devices  2   b   0  and  2   b   1  through a route  3   b  and the B IF  4   b.  The lines A and B operate synchronously and each has three error checkers (wherein the line A includes the error checker  7   a  and the error checkers in the processing devices  2   a   0  and  2   a   1 , and the line B includes the error checker  7   b  and the error checkers in the processing devices  2   b   0  and  2   b   1 ). The comparator  9  carries out a synchronization check between a signal  5   a  outputted from the line A and a signal  5   b  outputted from the line B. 
         [0006]    Output of the common unit  15  is inputted to the processing devices  2   a   0  and  2   a   1  through the A IF  4   a,  and to the processing devices  2   b   0  and  2   b   1  through the B IF  4   b.  Accordingly, a UE (uncorrectable error) in the common unit  15  propagates to the lines A and B when the processing devices read from the common unit. The UE is therefore detected on both the lines A and B. 
         [0007]    The selector generation unit  12  makes a determination based on a signal  10  outputted from the comparator  9 , a signal  8   a  outputted from the error checker  7   a,  a signal  8   b  outputted from the error checker  7   b,  a signal  11   a   0  outputted from the error checker inside the processing device  2   a   0 , a signal  11   a   1  outputted from the error checker inside the processing device  2   a   1 , a signal  11   b   0  outputted from the error checker inside the processing device  2   b   0 , and a signal  11   b   1  outputted from the error checker inside the processing device  2   b   1 . In accordance with a signal  13  indicating a determination result from the selector generation unit  12 , the selector  14  selects and outputs either the signal  5   a  or  5   b  to the common unit  15 . 
         [0008]    Described below is a case that an error checker detects a UE. 
         [0009]    Next, operation of receiving an error signal by the selector generation unit  12  will be described.  FIG. 26  is a table illustrating an operation example of receiving a UE signal by a conventional selector generation unit. This table represents content of the select signal  13  as outputted from the selector generation unit  12  in relation to content of line-A error signals (e.g., the signals  8   a,    11   a   0 , and  11   a   1 ), line-B error signals (e.g., the signals  8   b,    11   b   0 , and  11   b   1 ), and synchronization errors (comparison errors and the signal  10 ) inputted to the selector generation unit  12 , for each case number. 
         [0010]    The line-A error signals each indicates that a UE is detected by a line-A error checker, and the line-B error signals each indicates that a UE is detected by a line-B error checker. The synchronization error is an error of in synchronization between the lines A and B, and indicates that a comparison result from the comparator  9  indicates a disagreement (i.e., being out of synchronization). Content of the select signal  13  indicates one of signal  5   a,  signal  5   b  and an error stop (not selected and a system stop). If the content of the select signal  13  describes that “both of signal  5   a  and signal  5   b  are OK”, the selector generation unit  12  selects either the signal  5   a  or signal  5   b  in accordance with a predetermined determination method because the same operation is obtained regardless of whether the signal  5   a  or signal  5   b  is selected. The predetermined determination method is, for example, to select a preset line or a line selected in advance. 
         [0011]      FIG. 27  is a flowchart illustrating an operation example when a conventional selector generation unit receives an error signal. The selector generation unit  12  firstly determines whether a notification about a UE has been received or not (S 11 ). 
         [0012]    If a notification about a UE has been received (S 11 , Yes), the selector generation unit  12  determines where the UE has been received from (S 21 ). If the UE is an error from the line A (S 21 , line-A error), the selector generation unit  12  selects the signal  5   b  (S 22 ), and this flow ends. Otherwise, if the UE is an error from the line B (S 21 , line-B error), the selector generation unit  12  selects the signal  5   a  (S 23 ), and this flow ends. If the UE is an error which has been simultaneously notified of from both the lines A and B (S 21 , simultaneous), the selector generation unit  12  does not select any signal (S 24 , error stop), and this flow ends. 
         [0013]    If any notification about an UE has not been received (S 11 , No), the selector generation unit  12  makes a determination on a synchronization check result of the comparator  9  (S 61 ). If no synchronization error occurs (S 61 , no error), the selector generation unit  12  selects either the signal  5   a  or signal  5   b  in accordance with the determination method described previously (S 62 ), and this flow ends. Otherwise, if a synchronization error occurs (S 61 , synchronization error), the selector generation unit  12  does not select any signal (S 63 , error stop), and this flow ends. 
         [0014]    According to the operation of the selector generation unit  12 , if a comparison error is detected or errors are detected on both lines (case number=2, or 5 to 11 as illustrated in  FIG. 26 ), the information processing system stops. 
         [0015]    Next, operation of each error checker (the error checkers  7   a  and  7   b,  and the error checkers inside the processing devices  2   a   0 ,  2   a   1 ,  2   b   0 , and  2   b   1 ) will be described.  FIG. 28  is a flowchart illustrating an operation example of a conventional error checker. The error checker firstly determines what type of error has occurred (S 111 ). If no error has occurred (S 111 , No Error), the error checker does nothing, and this flow ends. If a UE has occurred (S 111 , UE), the error checker issues a notification about the UE to the selector generation unit  12  (S 112 ), and this flow ends. If a CE has occurred (S 111 , CE), the error checker corrects the CE (S 113 ), and this flow ends. 
         [0016]    For example, if a UE is detected on the line B, the selector  14  selects the signal  5   a  in accordance with the operation of the selector generation unit  12  as described above, and separates the line B from which an error has been detected. In a similar manner, if a UE is detected on the line A, the selector  14  selects the signal  5   b  in accordance with the operation of the selector generation unit  12  as described above, and separates the line A from which an error has been detected. In this manner, the system is protected. 
         [0017]    A further description will be made of a case that an error checker detects a CE (correctable error). If each of the lines is given a path for carrying out a CE processing in an interruptive manner, the line where a CE has been detected performs masking of an interruption processing. 
         [0018]    Several of conventional techniques relevant to the present invention are fault-tolerant computer devices which shorten a pause of device operation, and a resynchronization method thereof.
   [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-046599   
 
         [0020]    However, there is a case that the mirror mode is weaker against errors than a single mode, in a system in which a UE from the common unit  15  propagates to the lines A and B and an error is recognized by the lines A and B, and which has the selector generation unit  12  performing operation as described above, like in the information processing system described previously. 
       SUMMARY 
       [0021]    According to an aspect of the invention, an information processing device having two processing units capable of operating in synchronization with each other, includes: a common unit capable of outputting an identical signal to the two processing units; detection units that are respectively provided for the processing units and each detects errors occurred in corresponding processing unit respectively; a comparison unit that compares outputs from the two processing units; and a control unit that controls signals from the processing units to the common unit, based on a detection result of the detection units and a comparison result of the comparison unit, and determines, if errors of an identical type are simultaneously detected by the detection units, that the errors are due to an error of the common unit. 
         [0022]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0023]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a block diagram illustrating a configuration example of an information processing system according to a first embodiment of the invention; 
           [0025]      FIG. 2  is a table illustrating an operation example of receiving a UE signal by a selector generation unit according to the first embodiment; 
           [0026]      FIG. 3  is a flowchart illustrating an operation example of receiving an error signal by the selector generation unit according to the first embodiment; 
           [0027]      FIG. 4  is a block diagram illustrating a configuration example of an information processing system according to a second embodiment of the invention; 
           [0028]      FIG. 5  is a circuit diagram illustrating a configuration example of a CE recording unit according to the second embodiment; 
           [0029]      FIG. 6  is a flowchart illustrating an operation example of an error checker according to the second embodiment; 
           [0030]      FIG. 7  is a block diagram illustrating a configuration example of an information processing system according to a third embodiment of the invention; 
           [0031]      FIG. 8  is a table illustrating an operation example of receiving a CE signal by a selector generation unit according to the third embodiment; 
           [0032]      FIG. 9  is a flowchart illustrating a first processing in operation of receiving an error signal by the selector generation unit according to the third embodiment; 
           [0033]      FIG. 10  is a flowchart illustrating a second processing in the operation of receiving an error signal by the selector generation unit according to the third embodiment; 
           [0034]      FIG. 11  is a flowchart illustrating an operation example of an error checker according to the third embodiment; 
           [0035]      FIG. 12  is a block diagram illustrating operation of a processing step S 210  on a system board according to the third embodiment; 
           [0036]      FIG. 13  is a block diagram illustrating operation of a processing step S 220  on the system board according to the third embodiment; 
           [0037]      FIG. 14  is a block diagram illustrating operation of a processing step S 230  on the system board according to the third embodiment; 
           [0038]      FIG. 15  is a block diagram illustrating operation of a processing step S 240  on the system board according to the third embodiment; 
           [0039]      FIG. 16  is a block diagram illustrating operation of a processing step S 250  on the system board according to the third embodiment; 
           [0040]      FIG. 17  is a block diagram illustrating operation of a processing step S 260  on the system board according to the third embodiment; 
           [0041]      FIG. 18  is a block diagram illustrating operation of a processing step S 270  on the system board according to the third embodiment; 
           [0042]      FIG. 19  is a block diagram illustrating operation of a processing step S 280  on the system board according to the third embodiment; 
           [0043]      FIG. 20  is a block diagram illustrating operation of a processing step  5290  on the system board according to the third embodiment; 
           [0044]      FIG. 21  is a block diagram illustrating operation of a processing step S 310  on the system board according to the third embodiment; 
           [0045]      FIG. 22  is a block diagram illustrating operation of a processing step S 320  on the system board according to the third embodiment; 
           [0046]      FIG. 23  is a block diagram illustrating operation of a processing step S 410  on the system board according to the third embodiment; 
           [0047]      FIG. 24  is a block diagram illustrating operation of a processing step S 420  on the system board according to the third embodiment; 
           [0048]      FIG. 25  is a block diagram illustrating a configuration example of a conventional information processing system; 
           [0049]      FIG. 26  is a table illustrating an operation example of receiving a UE signal by a conventional selector generation unit; 
           [0050]      FIG. 27  is a flowchart illustrating an operation example of receiving an error signal by the conventional selector generation unit; and 
           [0051]      FIG. 28  is a flowchart illustrating an operation example of a conventional error checker. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0052]    There is a case that the mirror mode is weaker against errors than the single mode, in a system in which a UE from the common unit  15  propagates to the lines A and B and an error is recognized by the lines A and B, and which has the selector generation unit  12  performing operation as described above, like in the information processing system described previously. 
         [0053]    Described below will be a case that the processing device  2   a   0  incapable of recognizing poisoning data reads resources in the common unit  15 , targeting a UE. The poisoning data is data which is marked to indicate that an error has been detected if the error is detected in the data. In the case of the single mode, if a read target is UE when the processing device  2   a   0  reads the common unit  15 , the common unit  15  poisons the data and returns the data to the processing device  2   a   0 . Since the processing device  2   a   0  cannot recognize poisoning data, the error checker inside the processing device  2   a   0  recognizes the data as a UE, and can accordingly determine whether recording of an error log and continuation of the system are possible or not. In contrast, in the case of the mirror mode, if the common unit  15  returns poisoning data and if the error checkers inside the processing devices  2   a   0  and  2   b   0  simultaneously recognize UEs, signals  11   a   0  and  11   b   0  are simultaneously asserted because a UE is an error which is a target to cause separation of a line. The system then stops. 
         [0054]    If each of the lines is given a path for carrying out a CE processing in an interruptive manner when a CE is detected, recording of a CE log and continuation of the system are possible upon detection of a CE signal, in the single mode. However, masking for an interruption processing for a CE is carried out in the mirror mode, and therefore, recording of a CE log cannot be carried out. This is because, if an interruption processing is inserted in on a line in order to record an error log, both of the lines cannot be mutually synchronized any more. However, the recording of an error log is very important from a viewpoint of predictive monitoring. Therefore, there is a harmful influence on reliability of the mirror mode. 
         [0055]    Hereinafter, embodiments of the invention will be described with reference to the drawings. 
       First Embodiment 
       [0056]    At first, a configuration of an information processing system (information processing device) according to an embodiment of the invention will be described. 
         [0057]      FIG. 1  is a block diagram illustrating a configuration example of the information processing system according to this embodiment. In this figure, common reference symbols to  FIG. 25  denote the same or equivalent components as or to those in  FIG. 25 , descriptions of which will be omitted herefrom. Compared with  FIG. 25 ,  FIG. 1  includes a selector generation unit  12   p  in place of the selector generation unit  12 . 
         [0058]    Next, operation of the information processing system according to this embodiment will be described. 
         [0059]    As in the conventional information processing system described previously, the information processing system recognizes errors on lines A and B through which UEs of a common unit  15  propagate. 
         [0060]    Described next is an operation of receiving an error signal by the selector generation unit  12   p.    
         [0061]      FIG. 2  is a table illustrating an operation example of receiving a UE signal by the selector generation unit according to this embodiment. This figure is similar to  FIG. 26  but differs in that, if UEs are detected on the lines A and B and if there is no comparison error (case number=5, 7, or 9 illustrated in  FIG. 2 ), either the signal  5   a  or signal  5   b  is selected in accordance with the determination method described previously. 
         [0062]      FIG. 3  is a flowchart illustrating an operation example of receiving an error signal by the selector generation unit according to this embodiment. In this figure, common reference symbols to  FIG. 27  denote the same or equivalent components as or to those in  FIG. 27 , descriptions of which will be omitted herefrom. Compared with  FIG. 27 , a processing step S 31  is executed in this figure, in place of the processing step S 24 . In a processing step S 21 , if UEs are errors received simultaneously from both the lines A and B (S 21 , simultaneous), the selector generation unit  12   p  makes a determination on a synchronization check result from the comparator  9  (S 31 ). If there is no synchronization error (S 31 , no error), the selector generation unit  12   p  selects either the signal  5   a  or signal  5   b  in accordance with the method described previously (S 32 ), and this flow then ends. Otherwise, if there is a synchronization error (S 31 , synchronization error), the selector generation unit  12   p  does not select any signal (S 33 , error stop), and this flow then ends. 
         [0063]    Each of error checkers (the error checkers  7   a  and  7   b  and the error checkers inside the processing devices  2   a   0 ,  2   a   1 ,  2   b   0 , and  2   b   1 ) operates in the same manner as the error checker illustrated in  FIG. 28 . 
         [0064]    According to the selector generation unit  12   p  described above, for example, the processing devices  2   a   0  and  2   b   0  read resources in the common unit  15 . If UD is detected from a target thereof, the system is not stopped by the selector  14 , unlike in the conventional information processing system described previously, but the UE is recognized as a common unit error even if both the lines A and B simultaneously detect UEs. 
         [0065]    Even if errors are simultaneously detected on the lines A and B for some other reason, an error stop is determined in case of a comparison error (case number=6, 8, or 10 as illustrated in  FIG. 2 ) as a result of a synchronization check performed by the comparator  9 . Reliability of the system is therefore not damaged. 
         [0066]    According to this embodiment, if a common unit error which does not necessitate stop of the system propagates to the lines A and B, the error which has propagates to the lines A and B can be recognized to be a common unit error, leading to improvement in reliability of the mirror mode. 
       Second Embodiment 
       [0067]    At first, a description will be made of the configuration of the information processing system (information processing device) according to a second embodiment. 
         [0068]      FIG. 4  is a block diagram illustrating a configuration example of the information processing system according to this embodiment. In this figure, common reference symbols to  FIG. 25  denote the same or equivalent components as or to those in  FIG. 25 , descriptions of which will be omitted herefrom. Compared with  FIG. 25 , CE recording units  16   a  and  16   b  are newly provided in this figure. The CE recording unit  16   a  records logs of CEs detected by an error checker  7   a  and error checkers in the processing devices  2   a   0  and  2   a   1 . Similarly, the CE recording unit  16   b  records logs of CEs detected by an error checker  7   b  and error checkers inside the processing devices  2   b   0  and  2   b   1 . The logs recorded on the CE recording units  16   a  and  16   b  are read from outside the information processing system. 
         [0069]      FIG. 5  is a circuit diagram illustrating a configuration example of the CE recording units according to this embodiment. As illustrated in this figure, each of the CE recording units  16   a  and  16   b  is constituted by a simple counter circuit. The circuit counts and holds a number of errors by using a counter and a FF (flip-flop) each time when a CE signal is received. When the number of errors reaches a value Max, the circuit then keeps holding the number Max. 
         [0070]    Described next is an operation of each of error checkers (the error checkers  7   a  and  7   b  and the error checkers inside the processing devices  2   a   0 ,  2   a   1 ,  2   b   0 , and  2   b   1 ).  FIG. 6  is a flowchart illustrating an operation example of error checkers according to this embodiment. In this figure, common reference symbols to  FIG. 28  denote the same or equivalent components as or to those in  FIG. 28 , descriptions of which will be omitted herefrom. Compared with  FIG. 28 , a processing step S 123  is executed in this figure, in place of the processing step S 113 . In the processing step S 111 , if a CE occurs (S 111 , CE), the error checker corrects the CE and causes a connected CE recording unit to record an error log (S 123 ). This flow then ends. 
         [0071]    According to this embodiment, the lines A and B are provided with the CE recording units. Therefore, when a CE signal is detected by the line A or B, the CE signal is corrected while recording a log of the CE, so that the system is kept running without separating any line. Accordingly, actualization of collection of error logs, and application to predictive monitoring of hardware errors by using content of errors can be expected and lead to improvement in reliability of the mirror mode. 
       Third Embodiment 
       [0072]    At first, a description will be made of the configuration of an information processing system (information processing device) according to a third embodiment. 
         [0073]    In the information processing system according to this embodiment, resynchronization is possible even after a line A or line B is separated from the control system, and each of the lines has a mechanism of recording logs of CEs when CEs are detected. 
         [0074]      FIG. 7  is a block diagram illustrating a configuration example of the information processing system according to this embodiment. In this figure, common reference symbols to  FIG. 25  denote the same or equivalent components as or to those in  FIG. 25 , descriptions of which will be omitted herefrom. Compared with  FIG. 25 , a selector generation unit  12 q is provided in this figure, in place of the selector generation unit  12 . Processing devices  2   a   0 q,  2   a   1 q,  2   b   0 q, and  2   b   1 q are provided respectively in place of the processing devices  2   a   0 ,  2   a   1 ,  2   b   0 , and  2   b   1 . Further, there are provided a signal  16   a   0  for notifying the selector generation unit  12   q  of an error which has occurred in the processing device  2   a   0   q,  a signal  16   a   1  for notifying the selector generation unit  12   q  of an error which has occurred in the processing device  2   a   1   q,  a signal  16   b   0  for notifying the selector generation unit  12   q  of an error which has occurred in the processing device  2   b   0   q,  and a signal  16   b   1  for notifying the selector generation unit  12   q  of an error which has occurred in the processing device  2   b   1   q.    
         [0075]    The processing devices  2   a   0   q,    2   a   1   q,    2   b   0   q,  and  2   b   1   q  are, for example, CPUs each of which has a CE recording function to record logs of CEs in an interruptive manner when CEs are detected. 
         [0076]    Next, operation of the information processing system according to this embodiment will be described. 
         [0077]    Described first is an operation of receiving a CE signal by the selector generation unit  12   q.    
         [0078]      FIG. 8  is a table illustrating an operation example of receiving a CE signal by the selector generation unit according to this embodiment. This table represents content of a select signal  13  as outputted from the selector generation unit  12   q  in relation to content of line-A error signals (signals  16   a   0  and  16   a   1 ), line-B error signals (signals  16   b   0  and  16   b   1 ), and synchronization errors (a comparison error and a signal  10 ), for each case number. The content of the select signal  13  represents the signal  5   a,  signal  5   b,  or error stop. If the content of the select signal  13  describes that “both of  5   a  and  5   b  are OK”, the selector generation unit  12   q  may select either the signal  5   a  or  5   b,  and therefore, selects one of the signals  5   a  and  5   b  in accordance with the method described previously. 
         [0079]      FIG. 9  is a flowchart illustrating a first processing in the operation of receiving an error signal by the selector generation unit according to this embodiment.  FIG. 10  is a flowchart illustrating a second processing in the operation of receiving an error signal by the selector generation unit according to this embodiment. In  FIGS. 9 and 10 , common reference symbols to  FIG. 27  denote the same or equivalent components as or to those in  FIG. 27 , descriptions of which will be omitted herefrom. Firstly, the selector generation unit  12   q  determines whether a notification about an error has been received or not (S 1 ). 
         [0080]    If a notification about an error has been received (S 1 , Yes), the selector generation unit  12   q  determines whether the notification includes a UE or not (S 2 ). If a UE is included in the notification (S 2 , UE), the selector generation unit  12   q  executes the same processing as the conventional processing from the processing step S 21  thereof. If a CE is included in the notification (S 2 , CE Only), the selector generation unit  12   q  determines where the CE has occurred (S 71 ). 
         [0081]    If the CE is an error from the line A in the processing step S 71  (S 71 , line-A error), the selector generation unit  12   q  determines a synchronization check result from the comparator  9 . If there is no synchronization error (S 72 , no error), the selector generation unit  12   q  selects the signal  5   a  (S 73 ). If there is a synchronization error (S 72 , synchronization error), no signal is selected (S 74 , error stop) and this flow ends. 
         [0082]    Alternatively, if the CE is an error from the line B in the processing step S 71  (S 71 , line-B error), the selector generation unit  12   q  makes a determination on a synchronization check result from the comparator  9 . If there is no synchronization error (S 75 , no error), the selector generation unit  12   q  selects the signal  5   b  (S 76 ). Otherwise, if there is a synchronization error (S 75 , synchronization error), no signal is selected (S 77 , error stop) and this flow ends. 
         [0083]    Also alternatively, if the CE is an error which has been simultaneously notified of from both the lines A and B (S 71 , simultaneous), the selector generation unit  12   q  makes a determination on a synchronization check result from the comparator  9 . If there is no synchronization error (S 78 , no error), either the signal  5   a  or  5   b  is selected in accordance with the method described previously (S 79 ). Otherwise, if there is a synchronization error (S 78 , synchronization error), no signal is selected (S 80 , error stop) and this flow ends. 
         [0084]    If no notification about an error has been received (S 1 , No), the selector generation unit  12   q  executes the same processing as the conventional processing from the processing step S 61  thereof. 
         [0085]    Described next is an operation of each of error checkers (error checkers  7   a  and  7   b,  and error checkers inside the processing devices  2   a   0   q,    2   a   1   q,    2   b   0   q,  and  2   b   1   q ).  FIG. 11  is a flowchart illustrating an operation example of an error checker according to this embodiment. In this figure, common reference symbols to  FIG. 28  denote the same or equivalent components as or to those in  FIG. 28 , descriptions of which will be omitted herefrom. Compared with  FIG. 28 , a processing step S 133  is executed in this figure, in place of the processing step S 113 . If a CE occurs (S 111 , CE), an error checker corrects the CE and notifies a connected selector generation unit  12   q  of the CE (S 133 ). This flow then ends. 
         [0086]    The error checker in the processing device  2   a   0   q  sends an error signal  16   a   0  to the selector generation unit  12   q  when a CE is detected. The selector generation unit  12   q  which has received the CE signal selects a signal  5   a  for the line-A from which an error has been detected and separates the line B from which no error has been detected, from the system. Thereafter, the processing device  2   a   0   q  on the line where an error has been detected corrects the CE signal, and an error log is recorded in an interruptive manner owing to the CE recording function. 
         [0087]    After recording the log, the selector generation unit  12   q  connects the separated line B again to the system, and resynchronizes both lines. Therefore, synchronization of the system is maintained while recording logs of CEs. Since the processing devices records logs of CEs, there is no need of a mechanism for externally reading CE logs from outside. Therefore, the CE recording unit as used in the second embodiment need not be inserted. 
         [0088]    Next, an operation example of resynchronization will be described. 
         [0089]    In the following, operation of the resynchronization will be described referring to an example in which the information processing system according to this embodiment is expressed as a system board (SB)  60 , the processing devices  2   a   0   q,    2   a   1   q,    2   b   0   q,  and  2   b   1   q  are respectively expressed as CPU  70 , CPU  71 , CPU  72 , and CPU  73 , and the control system  1  is expressed as a north bridge  80 , respectively. 
         [0090]    Resynchronization in this embodiment is a technique of resynchronizing a CPU in a short time (within a timeout detection period of an OS) to achieve resynchronization while the OS is running. 
         [0091]    At first, the north bridge  80  detects a step-out of redundancy (synchronization) due to an error of the CPU on one line (S 210 ).  FIG. 12  is a block diagram illustrating operation of a processing step S 210  on a system board according to this embodiment. This figure illustrates a case that a problem occurs in the CPU  72  on the line B. The CPUs  70  and  72  constitute a redundant CPU pair based on synchronous operation, as well as the CPUs  71  and  73  a redundant CPU pair. 
         [0092]    Next, the north bridge  80  stops operation of the CPU bus connected to the problematic CPU  72 , and also stops commands from being thereafter issued from the CPU bus (S 220 ).  FIG. 13  is a block diagram illustrating operation of the processing step S 220  on the system board according to this embodiment. 
         [0093]    Next, the north bridge  80  notifies the other paired normal CPU bus constituting the redundant structure of the stop of one line (S 230 ).  FIG. 14  is a block diagram illustrating operation of the processing step S 230 . The north bridge  80  hereby notifies the normal CPUs  70  and  71  of the stop of the line B. 
         [0094]    Next, to restrict commands from outside, the north bridge  80  continues to retry external commands (S 240 ).  FIG. 15  is a block diagram illustrating operation of the processing step S 240  on the system board according to this embodiment. As illustrated in this figure, the north bridge  80  on the system board  60  is connected to the north bridge  81  on the system board (SB)  61  through a global address cross bar  62 . If the north bridge  81  on the system board  61  issues a command to the system board  60 , the command is sent through the global address cross bar  62  (S 241 ) to the system board  60  (S 242 ). The north bridge  80  on the system board  60 , which receives the command, then issues Retry for the system board  61 . This Retry is sent through the global address cross bar  62  (S 243 ) to the system board  61  (S 244 ). 
         [0095]    Next, the north bridge  80  issues a firmware instruction so as to retract CPU internal information which is least necessary for resynchronization, into the memory from the normal CPUs (S 250 ).  FIG. 16  is a block diagram illustrating operation of the processing step S 250  on the system board according to this embodiment. The north bridge  80  hereby instructs the normal CPUs  70  and  71  to retract CPU internal information into the memory  74 . 
         [0096]    Next, the normal CPUs  70  and  71  which have received the instruction from the north bridge  80  writes cache data (CPU internal information) into the memory  74  in accordance with the instruction (S 260 ).  FIG. 17  is a block diagram illustrating operation of the processing step S 260  on the system board according to this embodiment. 
         [0097]    Next, the north bridge  80  then clears a snoop tag (cache state information of respective CPUs) in the north bridge  80  at the time when writing of cache data from all normal CPUs into the memory is completed (S 270 ).  FIG. 18  is a block diagram illustrating operation of the processing step S 270  on the system board according to this embodiment. 
         [0098]    Next, the north bridge  80  issues CPU Reset simultaneously for each of the CPUs  70 ,  71 ,  72 , and  73 , and thereby restarts synchronous operation of the CPUs (S 280 ).  FIG. 19  is a block diagram illustrating operation of the processing step S 280  on the system board according to this embodiment. 
         [0099]    Next, the north bridge  80  initializes each of the CPUs  70 ,  71 ,  72 , and  73 , and thereby recovers the information, which has been retracted into the memory, on each pair of the CPUs (S 290 ).  FIG. 20  is a block diagram illustrating operation of the processing step S 290  on the system board according to this embodiment. 
         [0100]    Depending on a state at this time, one of the following two cases is executed. 
         [0101]    The first case is that initialization and recovery of internal information are completed for all the CPUs. At this time, the north bridge  80  releases restriction on external commands, which has been executed in the processing step S 240  (S 310 ).  FIG. 21  is a block diagram illustrating operation of the processing step S 310  on the system board according to this embodiment. 
         [0102]    Next, the north bridge  80  restarts operation (S 320 ), and resynchronization then ends.  FIG. 22  is a block diagram illustrating operation of the processing step S 320  on the system board according to this embodiment. As illustrated in this figure, when the north bridge  81  thereafter issues a command for the north bridge  80 , the command is sent through the global address cross bar  62  (S 321 ) to the north bridge  80  (S 322 ). The north bridge  80  receives and processes the command, and then issues a response to the north bridge  81 . The response is sent through the global address cross bar  62  (S 323 ) to the north bridge  81  (S 324 ). 
         [0103]    The north bridge  80  counts a number of executed resynchronizations, and sets in advance an upper limit to a number of allowable resynchronizations. When the number of executed resynchronizations ≧ the upper limit is satisfied, the north bridge  80  only stops a problematic CPU bus without performing any more resynchronization, and continues operation of the system on one single line including only normal CPU bus. 
         [0104]    The second case is that initialization of CPUs and recovery of internal information are not all complete but a step-out of synchronization occurs like in the processing step S 210  during resynchronization. In this case, the north bridge  80  suspends resynchronization and performs operation only on one single line including only normal CPU bus, and releases restriction of external commands which has been carried out in the processing step S 240  (S 410 ).  FIG. 23  is a block diagram illustrating operation of the processing step S 410  on the system board according to this embodiment. 
         [0105]    Next, the north bridge  80  restarts operation (S 420 ), and the resynchronization ends.  FIG. 24  is a block diagram illustrating operation of the processing step S 420  on the system board according to this embodiment. As illustrated in this figure, when the north bridge  81  thereafter issues a command for the north bridge  80 , the processing steps S 321  to S 324  are executed. 
         [0106]    According to this embodiment, software of each processing device on the lines A and B has a function to record a log when a CE signal is detected. When a CE signal is detected on one of the lines A and B, the remaining line from which the CE is not detected is separated from the system. In this manner, more detailed error logs than in the second embodiment can be collected with use of the software of each processing device. Since collection of detailed error logs is thus achieved, application of hardware errors to predictive monitoring can be expected and lead to improvement in reliability of the mirror mode. 
         [0107]    The first, second, and third embodiments described above may be combined with each other. 
         [0108]    The processing units correspond to the lines A and B in the embodiments. The detection units correspond to the error checkers in the embodiment. The comparison unit corresponds to a comparator in the embodiments. The control unit corresponds to the selector generation unit in the embodiments. The recording unit corresponds to the CE recording unit in the embodiments or the CE recording function of the processing device. 
         [0109]    The detection step corresponds to processing executed by the error checkers in the embodiments. The comparison step corresponds to processing executed by the comparator in the embodiments. The control step corresponds to processing executed by the selector generation unit in the embodiments. The recording step corresponds to processing executed by the CE recording unit in the embodiments or the CE recording function of the processing device. The resynchronization step corresponds to resynchronization in the embodiments. 
         [0110]    As has been described above, reliability of resynchronization operation can be improved according to the present invention. 
         [0111]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.