Abstract:
A method for comparing data in a computer system having at least two execution units, the comparison of the data taking place in a comparison unit and each execution unit processing input data and generating output data, wherein one execution unit specifies to the comparison unit that the next piece of output data is to be compared to a piece of output data of the at least second execution unit, and thereupon a comparison of the at least two output data takes place.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and a device for comparing output data of at least two execution units of a microprocessor. 
       BACKGROUND INFORMATION 
       [0002]    Transient errors, triggered by alpha particles or cosmic radiation, are an increasing problem for integrated circuits. Due to declining structure widths, decreasing voltages and higher clock frequencies, there is an increased probability that a voltage spike, caused by an alpha particle or by cosmic radiation, will falsify a logical value in an integrated circuit. The effect can be a false calculation result. In safety-related systems, such errors must therefore be detected reliably. 
         [0003]    In safety-related systems, such as an ABS control system in a motor vehicle, in which malfunctions of the electronic equipment must be detected with certainty, redundancies are normally provided for error detection, particularly in the corresponding control devices of such systems. Thus, for example, in known ABS systems, the complete microcontroller is duplicated in each instance, all ABS functions being calculated redundantly and checked for consistency. If a discrepancy appears in the results, the ABS system is switched off. 
         [0004]    Such processor units having at least two integrated execution units are also known as dual-core architectures or multi-core architectures. The different execution units (cores) execute the same program segment redundantly and in a clock-synchronized manner; the results of the two execution units are compared, and an error will then be detected in the comparison for consistency. 
       SUMMARY OF THE INVENTION 
       [0005]    If today&#39;s dual-core processors are to work in a comparison mode, the cores, or rather the execution units have to be identical to the greatest extent possible, so that the output signals are able to be compared in each clock pulse. However, with regard to certain security aspects, it is also advantageous if diversitary execution units are used. If the execution units are diversitary, however, the output signals of these execution units are no longer able to be compared in each clock pulse. 
         [0006]    It is an object of the present invention to compare the output signals of diversitary execution units. The present invention attains this object by the introduction of a control signal by which an execution unit signals a comparison unit that the piece of data output with this signal is to be compared to the piece of data of the other execution unit. Diversitary execution units and diversitary software may be used for this. Only the data to be compared and their format have to be comparable. It depends on the respective implementation, of the invention described here, whether the sequence in which the data, that are to be compared, are transmitted to the comparison unit also has to be identical. 
         [0007]    One of the execution units advantageously specifies to the comparison unit that the next output piece of data is to be compared to an output piece of data of the at least second execution unit, and thereupon a comparison of the at least two output data takes place. The at least two execution units expediently process the input data independently of each other. A specification that the next piece of output data is to be compared advantageously takes place by a comparison signal. The comparison signal and the output piece of data that is to be compared are advantageously output in a mutually unequivocally assignable manner. An identifier is expediently assigned to a piece of data that is to be compared, by which the comparison is triggered. All execution units whose output data are to be compared advantageously signal this to the comparison unit. The output data that are to be compared are buffered via at least one buffer memory in a specifiable sequence. One of the execution units advantageously specifies to the comparison unit that the next piece of output data is to be compared to a piece of output data of the at least second execution unit, and thereupon a comparison of the at least two output data takes place. In the device, advantageously at least one buffer memory is provided, which is developed in such a way that the data are buffered in a specifiable sequence and are then able to be supplied to the comparison unit. The buffer memory is advantageously a FIFO memory. This is advantageously implemented in a device as well as a computer system including this device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a multiprocessor system G 60  having two execution units G 10   a  and G 10   b , as well as a comparison unit G 20 . 
           [0009]      FIG. 2  shows a specific embodiment of a comparison unit G 20  having two waiting lists G 21   a  and G 21   b.    
           [0010]      FIG. 3  shows a specific embodiment of a comparison unit G 200  having two lists in each case, G 210   a , G 211   a  and G 210   b , G 211   b.    
       
    
    
     DETAILED DESCRIPTION 
       [0011]    In the following text, an execution unit may, in this instance, designate both a processor/core/CPU, as well as an FPU (floating point unit), a DSP (digital signal processor), a coprocessor or an ALU (arithmetic logical unit). The present invention relates to a multiprocessor system G 60  shown in  FIG. 1 , having at least two execution units G 10   a , G 10   b  and a comparison unit G 20 . Each of execution units G 10   a , G 10   b  has at least one output to corresponding system interfaces G 30   a , G 30   b . Registers, memories or peripherals such as digital outputs, digital-to-analog converters and communication controllers are able to be controlled via these interfaces. The output signals of execution units G 10   a , G 10   b  are able to be compared in comparison unit G 20 . In response to a difference, an error is detected and appropriate measures are able to be taken. The output data and/or addresses of the execution units are used for the comparison. Additional control signals may be submitted to a comparison. Independently of the selected output signals that are to be compared, we shall speak from here on of the piece of data that is to be compared to another piece of data. 
         [0012]      FIG. 1  shows a possible implementation for a multiprocessor system G 60  having two execution units G 10   a  and G 10   b . Comparison unit G 20  is activated by a control signal G 50   a , G 50   b  of execution units G 10   a , G 10   b . If an execution unit G 10   a , G 10   b  wants to pass on a piece of data to system interface G 30   a  or G 30   b  without this being intended to be compared, this is passed on without setting signals G 50   a , G 50   b . Comparison unit G 20  is thereby made unconcerned with these data. If an execution unit G 10   a , G 10   b  wants to pass on a piece of data to system interface G 30   a  or G 30   b , and if this piece of data is to be compared to a corresponding piece of data of the other execution unit G 10   a , Glob, then, in addition to the output signals of the execution unit that are required for a data transfer to the system interface, a signal G 50   a  in the case of G 10   a , G 50   b  in the case of G 10   b  is generated for comparison unit G 20 . These signals G 50   a  and G 50   b  are also generated by execution units G 10   a  and G 10   b . These signal to comparison unit G 20  that the piece of data transmitted to the system interface, optionally with the appertaining address, is to be compared to a corresponding piece of data of the respective other execution unit. The comparison takes place when the other execution units also transmits a piece of data to its system interface, and when, in the process, it also signals to comparison unit G 20  a comparison that is to be carried out. Signal G 50   a  in the case of G 10   a , G 50   b  in the case of G 10   b  for the comparison does not necessarily have to be generated simultaneously with the transmission of the piece of data by the execution unit, but in such a way that the signal is able to be assigned unequivocally to this piece of data (including the address). Comparison unit G 20  is in a position to stop the execution units temporarily, if necessary, via signals G 70   a , G 70   b . In this context, execution unit G 10   a  is stopped via signal G 70   a  and execution unit G 10   b  is stopped via signal G 70   b . The execution units are stopped until the appropriate signals G 70   a  and G 70   b  are canceled again by the comparison unit. 
         [0013]    In a first specific embodiment shown in  FIG. 2 , a possible implementation of comparison unit G 20  is described. For each connected execution unit, it has an internal waiting list. These waiting lists are constructed according to the FIFO principle (first in first out principle). In the implementation example shown in  FIG. 2 , these are waiting list G 21   a  for execution unit G 10   a  and waiting list G 21   b  for execution unit G 10   b . A waiting list has n entries, but at least one. If an execution unit signals, for a piece of data, that it is to be compared, this piece of data is stored in an entry in the waiting list. If there is no more free entry present in the waiting list, the appertaining execution unit is stopped via signal G 70   a  or G 70   b , respectively, shown in  FIG. 1 , until there is again a free entry in the waiting list. Alternatively, comparison unit G 20  may generate an error signal if an execution unit tries to place an additional piece of data into a waiting list that is already full. If at least one entry is present in all waiting lists of G 20 , (in this instance, G 21   a  and G 21   b ), then, according to the FIFO principle, in each case the first, (time-wise the oldest) entries are compared to each other via unit G 22 . If the compared data are different, an error signal is generated and the entries in the waiting lists are then ejected, that is, they are removed from them. In case the data are equal, they are also removed from the waiting lists. Alternatively, in the case of more than two waiting lists, a majority decision (voting) may be made. A common feature of this specific embodiment is that the data to be compared have to be supplied in the identical sequence of all connected execution units, so that they are sorted into the waiting lists in the correct sequence. For, the matter of which data are to be compared to which data is specified only via their position within the waiting lists. The closest to the front, or oldest entries within the waiting lists are always the ones to be compared. 
         [0014]    An additional specific embodiment of comparison unit G 20  is shown in  FIG. 3 , denoted there by G 200 . For each connected execution unit, comparison unit G 200  has lists G 210   a , G 210   b , in which the piece of data to be compared is stored. In addition to lists G 210   a , G 210   b , further lists G 211   a , G 211   b  exist, in which for every piece of data in lists G 210   a , G 210   b  an unequivocal ID is stored. If a list is full, the respectively assigned comparison unit is stopped via signals G 70   a  or G 70   b , respectively, shown in  FIG. 1 , or an error signal is triggered if the execution unit should attempt to place an additional piece of data into a list that is already full. A comparison of the data then takes place when, in all lists G 210   a , G 210   b  data having appertaining identical ID&#39;s exist in lists G 211   a , G 211   b . The data are compared and in response to a difference an error signal is generated. If they are equal, they are transmitted to connected system interfaces G 30   a , G 30   b , or to G 32  if the system interface is assigned to the comparison unit. After a comparison, independently of the result, the data are removed from lists G 210   a , G 210   b , and the appertaining ID&#39;s from lists G 211   a , G 211   b . If more than two lists exist, a majority decision may be made. It is a feature of this implementation that the data that are to be compared do not have to be supplied in the identical sequence by all connected execution units to comparison unit G 20 . Data are compared when data are present in both lists G 210   a  and G 210   b , and at least two equal ID&#39;s are present in the ID lists.