Abstract:
A semiconductor integrated circuit according to an aspect of the invention includes a plurality of master devices which issue data transfer requests, at least one slave device which performs data transfer in accordance with the data transfer requests, and a network which arbitrates the plurality of data transfer requests respectively issued from the plurality of master devices, and informs the slave device of the arbitration result, thereby performing data transfer between the master devices and the slave device, wherein when issuing the data transfer request, the master device informs the network of a period which extends from the issuance of the data transfer request to the start of the data transfer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-290178, filed Nov. 7, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor integrated circuit, and more particularly, it relates to a data transfer apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    In a data transfer apparatus, an operation module which issues a data transfer request accesses a memory controller via a network. A plurality of operation modules transmit command signals and data signals to the memory controller when issuing the data transfer requests. When a split transaction method is employed as a data transfer method, the transmission and reception of the command signals and the data signals are periodically independently controlled. 
         [0006]    A write operation is described below in the data transfer apparatus wherein there are provided two operation modules and the memory connected to the memory controller is a dynamic random access memory (DRAM). 
         [0007]    Assume a case where, in writing in the DRAM (write operation), the first and second operation modules issue write commands, and the network transfers a command signal of the first operation module to the memory controller before transferring a command signal of the second operation module to the memory controller. 
         [0008]    In this case, if a data signal of the first operation module is output at an extremely late timing after the memory controller has received the command signal and accepted the data transfer request, the data transfer of the second operation module cannot be executed until the data transfer of the first operation module finishes in order to observe the order of writing. 
         [0009]    That is, even if the data in the second operation module is already transmittable, the second operation module is put on standby until the data transfer of the first operation module finishes. Moreover, the network and the memory controller are also put on standby so that the data transfer is not executed. As a result, data transfer efficiency decreases. 
         [0010]    On the other hand, there is a method wherein the network arbitrates the data transfer requests of the operation modules before the data in the first and second operation modules are ready. However, in this method, the DRAM has to secure a certain period of time from address notification accomplished by the transmission and reception of the command signals to writing of the data signals. Therefore, in this case, the standby state is generated until the data transfer to the DRAM even if the data signals have arrived at the memory controller. Thus, the efficiency of the data transfer decreases, and in order to prevent this, it is necessary to provide a buffer circuit in a system and increase the buffer size. 
         [0011]    In a read operation (reading) as well, a problem similar to that in the write operation arises, and the whole system is put on standby, so that the data transfer efficiency decreases. 
         [0012]    For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-355271 has been disclosed as a technique that solves the above-mentioned problem. In the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-355271, the whole data transfer apparatus needs to be under central control, so that system design becomes more difficult as the system scale increases. Moreover, accesses are based on a major cycle, and the transfer efficiency therefore decreases, particularly when there is a variation in data transfer amount between the modules. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    A semiconductor integrated circuit according to an aspect of the invention comprising: 
         [0014]    a plurality of master devices which issue data transfer requests; at least one slave device which performs data transfer in accordance with the data transfer requests; and a network which arbitrates the plurality of data transfer requests respectively issued from the plurality of master devices, and informs the slave device of the arbitration result, thereby performing data transfer between the master devices and the slave device, wherein when issuing the data transfer request, the master device informs the network of a period which extends from the issuance of the data transfer request to the start of the data transfer. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0015]      FIG. 1  is a block diagram showing the basic configuration of a data transfer apparatus in an embodiment of the present invention; 
           [0016]      FIG. 2  is a timing chart showing a write operation of the data transfer apparatus in the embodiment of the present invention; 
           [0017]      FIG. 3  is a timing chart showing a read operation of the data transfer apparatus in the embodiment of the present invention; 
           [0018]      FIG. 4  is a block diagram showing the internal configuration of a network in the embodiment of the present invention; 
           [0019]      FIG. 5  is a block diagram showing the internal configurations of operation modules in the embodiment of the present invention; 
           [0020]      FIG. 6  is a block diagram showing the internal configuration of a memory controller in the embodiment of the present invention; 
           [0021]      FIG. 7  is a block diagram showing an application of the embodiment of the present invention; 
           [0022]      FIG. 8  is a block diagram showing one example of the internal configuration of a buffer circuit; 
           [0023]      FIG. 9  is a block diagram showing one example of the internal configuration of the buffer circuit; and 
           [0024]      FIG. 10  is a block diagram showing a modification of the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    An embodiment of the present invention will hereinafter be described in detail with reference to the drawings. 
       1. Outline 
       [0026]    The embodiment of the present invention relates to a semiconductor integrated circuit, and more particularly, it relates to a data transfer apparatus. 
         [0027]    The data transfer apparatus in the embodiment of the present invention is characterized in that when a plurality of master devices issue data transfer requests to a slave device, the master devices inform a network interposed between the master devices and the slave device of a period extending from the issuance of the requests to data transfer. 
         [0028]    As a concrete example, when data transfer processing is performed, the master device outputs, to the slave device, not only a command signal as the data transfer request but also a signal carrying information on latency between the command signal and a data signal input/output in accordance with the command signal (hereinafter referred to as a latency signal). That is, the latency signal is input to the network in addition to the command signal and the data signal, which allows input/output between the master device and the slave device. In the present embodiment, for example, the latency signal indicates the number of cycles from the input of the command signal to the slave device to the start of the data transfer between the master device and the slave device. Moreover, in the present embodiment, the network arbitrates the order of the data transfer requests of a plurality of master devices on the basis of this latency signal. 
         [0029]    Thus, even when a plurality of master devices and a slave device are provided in one data transfer apparatus, the order of data transfer can be arbitrated on the basis of this latency signal. This enables the data transfer to be executed without generating the standby state of the data transfer. Thus, according to the embodiment of the present invention, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0030]    It is to be noted that in the embodiment of the present invention, the slave device is a device whose operation is controlled on the basis of the data transfer request issued from the master device. 
       2. Embodiment 
       [0031]    (1) Basic Configuration 
         [0032]    (a) Circuit 
         [0033]    The semiconductor integrated circuit in the embodiment of the present invention is described with  FIG. 1 . 
         [0034]    The semiconductor integrated circuit in the embodiment of the present invention is, for example, a data transfer apparatus.  FIG. 1  shows the basic configuration of a data transfer apparatus  1 . This data transfer apparatus  1  comprises a plurality of operation modules PE 1 , PE 2 , a network NW, a memory controller MC and a memory module  2 . 
         [0035]    In this data transfer apparatus  1 , for example, command transfer and data transfer are respectively controlled by temporally independently executed protocols based on a split transaction method. In the data transfer apparatus  1  of the present embodiment, the operation modules PE 1 , PE 2  function as master devices, and the memory controller MC and the memory module  2  function as slave devices whose operations are controlled by the plurality of operation modules PE 1 , PE 2  that are master devices. 
         [0036]    The plurality of operation modules PE 1 , PE 2  are connected to the network NW. When executing data transfer, each of the operation modules PE 1 , PE 2  issues a data transfer request (e.g., a command signal Cmd) to the network NW, and outputs the command signal Cmd as the data transfer request to the memory controller MC via the network NW. In accordance with this command signal Cmd, the operation modules PE 1 , PE 2  as the master devices control the operations of the memory controller MC and the memory module  2  as the slave devices, and input/output data signals Data. The operation modules PE 1 , PE 2  are, for example, central processing units (CPUs), direct memory access (DMA) controllers or digital signal processors (DSPs). In addition, although two operation modules are shown for simplicity in explanation in the present embodiment, there is not limit in number, and three or more operation modules may be connected to the network NW. 
         [0037]    The network NW arbitrates the order of data transfer for the data transfer requests (command signals) respectively issued from the plurality of operation modules, when these requests are simultaneously issued. Then, on the basis of the arbitration result, data is transferred between the operation module whose request has been accepted and the memory controller as well as the memory module in accordance with the data transfer requests (command signals) issued from the operation modules PE 1 , PE 2 . For example, a crossbar method or a common bus method is used for the network NW. 
         [0038]    The memory controller MC is connected to the network NW. The memory controller MC accepts the data transfer requests from the operation modules PE 1 , PE 2  input via the network NW, and manages an operation schedule for the data transfer between the operation modules PE 1 , PE 2  whose requests have been accepted and the predetermined memory module  2  to which the data is to be transferred. 
         [0039]    The memory module  2  is connected to the memory controller MC, and the operation schedule of this memory module  2  is managed by the memory controller MC. Thus, the requested data transfer is executed between the memory module  2  and the predetermined operation modules PE 1 , PE 2  via the memory controller MC and the network NW. For example, a DRAM, a static random access memory (SRAM) or a flash memory is used for the memory module  2 . Moreover, it may be an embedded memory module in which a memory chip and an LSI chip are mixed. 
         [0040]    In addition, the data transfer apparatus  1  shown in  FIG. 1  shows the basic configuration in the embodiment of the present invention, and may further have other components. 
         [0041]    The data transfer apparatus  1  in the embodiment of the present invention is characterized in that when the operation modules PE 1 , PE 2  issue the data transfer requests (command signals), the network NW interposed between the operation modules PE 1 , PE 2  and the memory controller MC as the slave device is informed of not only the command signal Cmd but also a period extending from the issuance of the data transfer requests to the start of the data transfer. 
         [0042]    In the present embodiment, this period corresponds to the operation clock of the data transfer apparatus, and is indicated by the number of cycles (latency) from the issuance of the command signals to the start of the transfer of the data signals. 
         [0043]    That is, the operation modules PE 1 , PE 2  output signals carrying latency information (latency signals) to the network NW in addition to the command signals. Moreover, the latency signals are also output to the memory controller MC as the slave device, for example, via the network NW. The network NW arbitrates the order of the data transfer processing on the basis of a latency signal ReqDataLat. Then, the data transfer is carried out between the operation modules PE 1 , PE 2  and the memory module  2  in the arbitrated order. Details of the method of arbitrating the data transfer by the network NW will be described later. 
         [0044]    Conventionally, when a plurality of operation modules are provided in one data transfer apparatus, the data transfer processing is carried out in accordance with a priority order preset for the respective operation modules. That is, the data transfer processing is carried in accordance with the set priority order, so that even when the data transfer processing for the operation module with a low priority order is ready, the data transfer processing for the operation module with the low priority order is put on standby if the data transfer processing for the operation module with a high priority order has not been executed and completed. This causes the whole system to be put on standby and contributes to a decrease in the data transfer efficiency of the data transfer apparatus. 
         [0045]    On the contrary, in the embodiment of the present invention, the data transfer processing is executed in the order arbitrated on the basis of the latency signal ReqDataLat. That is, according to the present embodiment, a cycle which enables the data transfer processing to be started is determined from the values of the latency signals ReqDataLat output from the plurality of operation modules PE 1 , PE 2 , and the order of the data transfer processing is arbitrated by the network NW so that the standby state of the system is not generated. Therefore, according to the embodiment of the present invention, it is possible to inhibit the standby state of the data transfer processing and improve the data transfer efficiency of the data transfer apparatus  1 . Such an effect of the present embodiment is higher particularly in the case of a data transfer apparatus (semiconductor integrated circuit) using a DRAM which has a time lag from the start of control over the slave devices (the memory controller MC and the memory module  2 ) to actual data transfer. 
         [0046]    Furthermore, the value indicated by the latency signals ReqDataLat is changed as needed with the size of a data signal Data and with how each operation module operates, so that the data transfer processing requested by a user can be flexibly handled. 
         [0047]    Still further, according to the present embodiment, buffer circuits for improving the data transfer efficiency can be reduced, so that the buffer size in the system can be reduced, and the system scale of the data transfer apparatus  1  can be reduced. 
         [0048]    As described above, according to the embodiment of the present invention, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit (data transfer apparatus). 
         [0049]    (b) Write Operation 
         [0050]    A write operation in the data transfer apparatus shown in the embodiment of the present invention is next described with  FIG. 2 .  FIG. 2  is a timing chart showing the write operation of the data transfer apparatus in the present embodiment. First, signals shown in  FIG. 2  are explained. 
         [0051]    The command signal Cmd indicates the kind of the data transfer request issued by the operation module PE 1 , PE 2 . An enable signal Ack indicates that the command signal Cmd has been accepted by the memory controller MC. A data transfer size signal Size is a signal indicating the size (volume) of data to be transferred and is corresponding to a period of the data transfer. A write valid data signal WDataValid is a signal indicating that the data signal Data is valid in a particular cycle. A write data enable signal WDataAck is a signal indicating that the data signal Data has been accepted by the memory controller MC. Then, the latency signals ReqDataLat are output from the operation modules PE 1 , PE 2  together with the command signals Cmd, and indicate the period from the output of the command signals Cmd to the start of the transfer of the data signals. In addition, an address signal indicating the transfer destination of the data signal Data is also output simultaneously with the command signal Cmd, but the address signal is not described here. 
         [0052]    The write operation in the present embodiment is described below on the assumption that there is no delay (latency) in the network NW and the network NW is capable of data transfer with zero latency for simplicity. In addition, in the present embodiment, preferential data transfer is carried out in the preset priority order of the operation modules, for example, in the order of the operation module PE 1  and the operation module PE 2  when the data transfer requests are issued from the plurality of operation modules PE 1 , PE 2  with difference timings. 
         [0053]    First, as shown in  FIG. 2 , at the first cycle of the operation clock CLK of the data transfer apparatus, the two operation modules PE 1 , PE 2  shown in  FIG. 1  simultaneously issue the data transfer requests (command signals) for executing the write operation to the memory controller MC via the network NW. At this moment, the command signals Cmd indicating write operations wr 1 , wr 2  are simultaneously output from the two operation modules PE 1 , PE 2  to the memory controller MC via the network NW. Moreover, the latency signals ReqDataLat are also output from the operation modules PE 1 , PE 2  to the memory controller MC via the network NW together with the command signals Cmd. 
         [0054]    With regard to the latency signals ReqDataLat, the cycle of the data output from the two operation modules PE 1 , PE 2  is determined by the network NW on the basis of the values indicated by the latency signals, and the order of the data transfer processing for the operation modules PE 1 , PE 2  is arbitrated by an arbitration method described later. In the example shown in  FIG. 2 , the respective latency signals ReqDataLat indicate that the data output of the operation module PE 1  is executed three cycles later and the data output of the operation module PE 2  is executed one cycle later. That is, the data transfer processing for the operation module PE 2  is ready earlier than the data transfer processing for the operation module PE 1 . Therefore, the network NW arbitrates and sets the order of the data transfer processing so that the write operation of the operation module PE 1  is executed after the write operation of the operation module PE 2  has been executed. 
         [0055]    Furthermore, the command signals Cmd and the latency signals ReqDataLat are input to the memory controller MC. On the basis of the result of the arbitration by the network NW, the enable signal Ack is output from the memory controller MC to the operation module PE 2  and then to the operation module PE 1 . 
         [0056]    When the enable signal Ack is input to the operation module PE 2  at the second cycle, the data transfer processing is immediately executed in the operation module PE 2  because the data signal Data to be output has already been prepared. Therefore, data valid signals DataValid and the write data enable signals WDataAck in the operation module PE 2  and the memory controller MC become active at the second to third cycles, and the data transfer for the write operation of the operation module PE 2  to the memory controller MC and the memory module  2  is executed. Further, the data transfer processing for the operation module PE 2  is completed at the third cycle. 
         [0057]    On the other hand, in the operation module PE 1 , the preparation for the output of the data signal Data is completed at the third cycle from the transmission of the command signal Cmd even if the enable signal Ack is input at the third cycle. Therefore, in the operation module PE 1 , the data valid signal DataValid and the write data enable signal WDataAck become active synchronously with the fourth cycle of an operation clock CLK, and the data transfer for the write operation is executed. The data transfer processing for the operation module PE 1  is completed at the fifth cycle. In addition, as described above, the data transfer for the operation module PE 2  is executed while the operation module PE 1  is preparing the data signal Data to be transmitted, so that the standby state of the data transfer is not generated in the data transfer apparatus. 
         [0058]    The write operation in the data transfer apparatus of the present embodiment is completed by the above-mentioned operation. In addition, in the above-mentioned operation, the value indicated by the latency signal ReqDataLat only represents the value of the latency from the output of the command signals Cmd of the operation modules PE 1 , PE 2  to the output of the data signal Data. However, when the size of the command signal Cmd is large, the timing for the data transfer may be delayed in accordance with the size. Therefore, it is preferable for the value indicated by the latency signal ReqDataLat to be changed in consideration of the size of the command signal. 
         [0059]    In the case where the priority order of the data transfer request of the operation module PE 1  is set higher than the operation module PE 2  and the data transfer is executed in accordance with the priority order as has been the case heretofore, if the memory controller MC accepts the simultaneously issued data transfer requests, the data transfer for the operation module PE 2  is executed after the data transfer for the operation module PE 1  has been finished, so that a standby state is generated in the system from the second to third cycle. As a result, the data transfer processing for the two operation modules PE 1 , PE 2  is completed at or after the seventh cycle, which reduces the data transfer efficiency of the data transfer apparatus. 
         [0060]    However, in the present embodiment, the network NW determines the output cycles of the data signals Data from the latency signals ReqDataLat output from the operation modules PE 1 , PE 2 , and arbitrates the order of the write operations. That is, in the data transfer apparatus  1  in the present embodiment, the data transfer processing for the write operations is continuously executed in consideration of the latencies of the plurality of operation modules PE 1 , PE 2  so that the standby state of the system is not generated. Thus, in the data transfer apparatus  1  in the present embodiment, the data transfer processing can be completed at the fifth cycle. 
         [0061]    Consequently, in the write operation of the data transfer apparatus in the embodiment of the present invention, the data transfer processing can be accomplished without generating a standby state in the data transfer processing. 
         [0062]    Therefore, according to the embodiment of the present invention, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0063]    (c) Read Operation 
         [0064]    A read operation in the data transfer apparatus shown in the first embodiment of the present invention is described with  FIG. 3 . It is to be noted that the same signs are assigned to the same signals as in the write operation and such signals are not described in detail. A read valid data signal RDataValid shown in  FIG. 3  is a signal indicating that the data signal Data is valid in a particular cycle, and a read data enable signal RdataAck is a signal indicating that the data signal Data has been accepted by the memory controller MC. 
         [0065]    First, as in the write operation, the data transfer requests for the execution of the read operation are issued from the operation modules PE 1 , PE 2  at the first cycle of the operation clock CLK, and the command signals Cmd indicating read operations rd 1 , rd 2  are simultaneously output to the memory controller MC via the network NW. In conjunction with this, the latency signals ReqDataLat are also output from the operation modules PE 1 , PE 2  to the memory controller MC via the network NW. 
         [0066]    The network NW determines the cycle of data input to the two operation modules PE 1 , PE 2  from the values of the latency signals ReqDataLat. 
         [0067]    In the example shown in  FIG. 3 , the respective latency signals ReqDataLat indicate that the data output of the operation module PE 1  can be input three cycles later and the data output of the operation module PE 2  can be input one cycle later. Therefore, the network NW arbitrates the order of the processing of data transfer from the memory module  2  to the operation modules PE 1 , PE 2  so that the read operation of the operation module PE 1  is executed after the read operation of the operation module PE 2  has been executed. Thus, the enable signal Ack is output from the memory controller MC to the operation module PE 2  and then to the operation module PE 1 . 
         [0068]    In the operation module PE 2 , the enable signal Ack is input at the second cycle. As the operation module PE 2  is ready to receive the data signal Data, the data transfer processing is immediately executed. Therefore, the read data valid signal RDataValid and the read data enable signal RdataAck in the operation module PE 2  and the memory controller MC become active at the second to third cycles, and the data transfer for the read operation in the operation module PE 2  is executed. Further, the data transfer processing for the operation module PE 2  is completed at the third cycle. 
         [0069]    On the other hand, in the operation module PE 1 , the preparation for receiving the data signal Data is completed at the third cycle from the output of the command signal Cmd even if the enable signal Ack is input at the third cycle. Therefore, in the operation module PE 1 , the read data valid signal RDataValid and the read data enable signal RdataAck become active synchronously with the fourth cycle of the operation clock CLK at which the read operation of the operation module PE 2  has been completed, and the data transfer for the read operation is executed. 
         [0070]    The read operation in the data transfer apparatus of the present embodiment is completed by the above-mentioned operation. 
         [0071]    As described above, in the read operation of the data transfer apparatus in the embodiment of the present invention, the data transfer processing can be accomplished without generating a standby state in the data transfer processing, as in the write operation. 
         [0072]    Therefore, according to the embodiment of the present invention, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0073]    (2) Examples 
         [0074]    Examples of the components in the data transfer apparatus  1  shown in  FIG. 1  are described below in more detail with  FIG. 4  to  FIG. 6 . It is to be noted that the same signs are assigned to the same parts as those described above and such parts are not described in detail. 
         [0075]    (a) Network 
         [0076]    An example of a network NW used in the data transfer apparatus  1  shown in  FIG. 1  is described with  FIG. 4 . As described above, the network NW makes arbitration when data transfer requests are simultaneously issued from a plurality of operation modules PE 1 , PE 2  in the data transfer apparatus  1 . 
         [0077]    As shown in  FIG. 4 , the operation modules PE 1 , PE 2  are connected to the network NW, and a multiplexer  10  and an arbiter  11  are provided on the network NW. 
         [0078]    The operation modules PE 1 , PE 2  output command signals Cmd and latency signals ReqDataLat, and data signals Data are input and output accordingly. 
         [0079]    The command signals Cmd, the latency signals ReqDataLat and the data signals Data are input to the multiplexer  10  in the network NW. Moreover, the command signals Cmd and the latency signals ReqDataLat are input to the arbiter  11  in the network NW. 
         [0080]    The arbiter  11  arbitrates the data transfer requests of the operation modules PE 1 , PE 2  on the basis of the input command signals Cmd and latency signals ReqDataLat. Then, the arbiter  11  outputs a control signal based on the result of the arbitration to the multiplexer  10 . The multiplexer  10  outputs one of the input command signals Cmd and one of the input latency signals ReqDataLat of the two operation modules PE 1 , PE 2  to a memory controller MC by the control signal, and then outputs the other data transfer request to the memory controller MC. 
         [0081]    Thus, the network NW arbitrates the order of the data transfer processing, and inputs and outputs the data signals Data. 
         [0082]    Several examples of arbitration methods performed by the network NW are described below. 
         [0083]    (i) First Arbitration Method 
         [0084]    In a first arbitration method, arbitration is made by comparing the values of a plurality of latency signals input to the arbiter  11 . Specifically, the network NW in this arbitration method makes an arbitration to execute data transfer so that the data transfer request with a smaller latency signal value is given priority out of the data transfer requests of the operation modules PE 1 , PE 2 . 
         [0085]    According to the first arbitration method, the arbiter  11  can be realized by a simple circuitry such as a comparator, and the priority order of the data transfer requests can be determined quickly. 
         [0086]    (ii) Second Arbitration Method 
         [0087]    As described above, in the embodiment of the present invention, the priority order of the operation modules is set in advance for the case where the data transfer requests are issued with no overlap. 
         [0088]    In a second arbitration method, when the sum of the value of the latency signal ReqDataLat of a certain operation module and the value of a corresponding data transfer size signal Size is equal to or less than the value of the latency signal ReqDataLat of the operation module set to a high priority degree, even the data transfer request of the operation module with a low priority order is accepted so that the order of data transfer is reversed regardless of the preset priority order, thereby carrying out data transfer. 
         [0089]    If the value of the data transfer size signal Size is high as described above, the data transfer may be delayed. Therefore, in the second arbitration method, the order of the data transfer requests is arbitrated according not only to the magnitude of the value of the latency signal ReqDataLat but also latency attributed to the value of the data transfer size signal Size, so that even if the value of the latency signal of the operation module set to a high priority order is high, the data transfer request can be executed first. 
         [0090]    Consequently, according to the second arbitration method, it is possible to avoid unnecessary delay of the data transfer request of the operation module with a high priority order. 
         [0091]    (iii) Third Arbitration Method 
         [0092]    In a third arbitration method, when the value of the latency signal of a certain operation module is higher than a preset threshold value, the data transfer request of the certain operation module is not accepted even if there are no data transfer requests from other operation modules. 
         [0093]    When a data transfer request (command signal Cmd) with a high latency signal ReqDataLat value is accepted, the command signal is only input, and actual data transfer is not executed for a long time. Thus, even if a data transfer request with a low latency signal ReqDataLat value is input later, data transfer cannot be executed, which substantially leads to the standby state of the system. 
         [0094]    However, as in the third arbitration method, the threshold value is set, and if the data transfer request corresponding to the latency signal ReqDataLat higher than the threshold value is not accepted, it is possible to accept and execute a data transfer request which is input later and which corresponds to the latency signal ReqDataLat lower than the threshold value, and avoid the situation where data transfer is not executed for a long time in the data transfer apparatus  1 . 
         [0095]    In addition, it is preferable for the threshold value set in the third arbitration method to be calculated on the basis of a value which is an addition of latency from the arbiter  11  to the memory controller MC to latency from the issuance of an address in the memory module to the input/output of data. In addition, the threshold value can be desirably changed during operation in the third arbitration method. Moreover, the third arbitration method can be used together with the first or second arbitration method. 
         [0096]    As described above, the arbiter  11  for arbitrating the data transfer requests from a plurality of operation modules is provided in the network NW for the arbitration of data transfer requests shown in  FIG. 4 , and the data transfer efficiency of the semiconductor integrated circuit can be improved by employing one of the arbitration methods shown in (i) to (iii). 
         [0097]    (b) Operation Modules 
         [0098]    An example of the operation modules used in the data transfer apparatus  1  shown in  FIG. 1  is described with  FIG. 5 . 
         [0099]    As shown in  FIG. 5 , a plurality of operation modules PE 1 , PE 2  are connected to one network NW. 
         [0100]    Each of the operation modules PE 1 , PE 2  has a controller  30 , data buffers  31 ,  33 , and an operator  32  therein. The buffers  31 ,  33  are, for example, instruction cache memories or data cache memories. Moreover, the operator  32  is, for example, a DSP, and the operator  32  is hereinafter called a DSP  32 . However, the operator  32  may be a CPU. In addition, the internal configurations of the operation modules PE 1 , PE 2  are not limited to the configurations shown in  FIG. 5 . For example, they may be DMA controllers including no explicit operators. 
         [0101]    The controller  30  controls the overall operations of the operation modules PE 1 , PE 2 . The buffer  31  stores, via the controller  30 , data input in the operation modules PE 1 , PE 2 . The DSP  32  operates the data retained in the buffer  31 . The buffer  33  retains the data operated by the DSP  32 , and outputs the data to the controller  30 . Then, the controller  30  outputs the operated data to a memory module  2  via the network NW and a memory controller MC. Thus, the data in the memory module  2  is rewritten to the operated data. Such processing is performed in each of the operation modules PE 1 , PE 2  every time the data transfer processing is carried out. 
         [0102]    Here, for example, when it is predicted that one operation for the operation module PE 1  finishes in 100 cycles, the operation module PE 1  outputs a write command signal or a read command signal as a data transfer request to the network NW simultaneously with the start of the operation. Further, this command signal is output from the network NW to the memory controller MC. The value of a latency signal issued simultaneously with this command signal is set at, for example, “100”. When the latency signal is set in this manner, the memory controller MC performs scheduling for the memory module  2  on the assumption that the data transfer processing is started 100 cycles later. 
         [0103]    Thus, with appropriate operation timing, the memory controller MC can control the memory module  2  for example, the output of an address signal to the memory module  2 . 
         [0104]    As described above, in the operation processing in the operation modules PE 1  to PE 2  whose operation cycles are predicted, a schedule is previously set, before the end of the operation processing, in the memory module  2  to which the results of the operations are transferred, such that it is possible to reduce, for example, the standby state of the data transfer processing and also reduce data latency in the operation modules and thus improve the operation processing efficiency. Consequently, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0105]    (c) Memory Controller 
         [0106]    An example of the memory controller MC used in the data transfer apparatus  1  shown in  FIG. 1  is described with  FIG. 6 . As described above, in the embodiment of the present invention, the data transfer requests issued from a plurality of operation modules are arbitrated by the network NW on the basis of the latency signal. 
         [0107]    The memory controller MC having an internal configuration shown in  FIG. 6  accepts the arbitration result, and performs scheduling for the memory module  2 . As shown in  FIG. 6 , the latency signal ReqDataLat is input to a subtracter  40  provided in the memory controller MC. An offset value retained in a register  41  is further input to the subtracter  40 . Then, the subtracter  40  subtracts the offset value from the value of the input latency signal ReqDataLat. Thus, the latency before access control can be started (hereinafter referred to as access start enable latency) is found. This offset value is preferably set on the basis of, for example, the value of CAS latency of the memory module  2 . In addition, the CAS latency is the latency required from the output of a CAS signal designating an address of a column to the actual execution of the writing/reading of the data signal. 
         [0108]    Furthermore, a counter  44  is provided in the memory controller MC. This counter  44  is always incremented by an adder  43  on a regular cycle during the operation of the data transfer apparatus. The value of the counter  44  obtained by the increment indicates a “current time” in the memory controller MC. The “current time” is updated by the increment simultaneously with the operation cycle of the whole data transfer apparatus  1  or the operation cycles of the operation modules PE 1 , PE 2 . 
         [0109]    Furthermore, the “access start enable latency” and the “current time” are added together by an adder  42 , and this additional value indicates the time at which the control of the access to the memory module can be started (hereinafter referred to as “access start enable time”). 
         [0110]    The value of the access start enable time is retained in a plurality of registers  46  provided in the memory controller MC for the respective corresponding command signals Cmd. In addition, the registers  46  are first-in first-out (FIFO) type registers, and the registers  46  are hereinafter called FIFOs  46 . At the same time, data signals Data corresponding to the command signals Cmd are retained in registers  47 , respectively. 
         [0111]    The value of the “access start enable time” stored in the FIFOs  46  is compared by a comparator  45  with the value of the “current time” indicated by the counter  44 . 
         [0112]    Furthermore, an enable bit of the FIFO in which the “access start enable time” coincides with the “current time” or in which the “access start enable time” is equal to or less than the “current time” becomes active, so that the command signal Cmd retained in that FIFO is validated. The validated command signal Cmd, an address signal Address indicating the input/output end of data, and the data signal Data retained in the register  47  corresponding to the command signal Cmd are output to the memory module  2  after physical and electric conversions such as digital/analog conversion and voltage conversion by a physical layer circuit (PHY)  48 . Then, the operation of writing to or reading from the memory module  2  is started, and the data transfer is executed. Such a comparison between the “access start enable time” and the “current time” is sequentially performed for each of the FIFOs  46 , and data transfers are sequentially performed for the command signals Cmd satisfying the condition. In addition, when there is no delay or there is a small delay attributed to a circuit such as the PHY  48  provided after the comparator  45 , this access start enable time is the time at which the data transfer is substantially started (data transfer enable time). 
         [0113]    Thus, the data transfer processing is executed between the operation modules PE 1 , PE 2  and the memory module  2  via the network NW. 
         [0114]    As described above, the memory controller MC shown in  FIG. 6  performs scheduling for the memory module  2  so that the command signal is executed in which the value of the “access start enable time (data transfer start time)” based on the latency signal and reflecting the result of the arbitration by the network NW is equal to or less than the “current time” indicated by the counter  44  in the memory controller MC. Thus, the memory controller MC can manage the operation of the memory module  2  on the basis of the latency signal ReqDataLat, and regulate the timing of the data transfer. 
         [0115]    Consequently, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0116]    In addition, one memory controller MC is provided in the example shown in  FIG. 6 , but the present invention is not limited to this, and a plurality of memory controllers of a similar configuration may be provided. When a plurality of memory controllers MC are provided, the command signal Cmd is selected in such a manner as to improve the efficiency of the access to the memory module  2 , thereby making it possible to improve the data transfer efficiency. Moreover, the internal configuration of the memory controller MC may be such that the timing of the data transfer to the memory module  2  (execution of the command signal Cmd) can be regulated in accordance with the latency signal ReqDataLat input to the memory controller MC, and the internal configuration of the memory controller MC is not limited to the configuration shown in  FIG. 6 . 
         [0117]    (3) Application 
         [0118]    An application of the embodiment of the present invention is described with  FIG. 7  to  FIG. 9 . It is to be noted that the same signs are assigned to the same members as those described above and such members are not described in detail. 
         [0119]      FIG. 7  shows a data transfer apparatus  1 A in the application of the embodiment of the present invention. 
         [0120]    As shown in  FIG. 7 , buffer circuits  3  are inserted in data transfer paths within the data transfer apparatus  1 A, such that command signals Cmd or data signals Data are pipeline-processed. According to this configuration, it is possible to prevent the decrease of an operation frequency, and provide a data transfer apparatus  1 A of a large scale and of a high operation frequency. 
         [0121]    However, in such a case, a latency caused by the inserted buffer circuits  3  is generated. Therefore, if a latency signal ReqDataLat is provided in addition to the command signal Cmd and the data signal Data as in the embodiment of the present invention, it may be possible to not achieve consistency of latency between operation modules PE 1 , PE 2  and a memory controller MC. Thus, the buffer circuit  3  which can assure the consistency of latency will be described with  FIG. 8  and  FIG. 9 . 
         [0122]    In the buffer circuit  3  shown in  FIG. 8 , a command signal is input to an internal buffer  20 , and one cycle passes when the command signal passes through the internal buffer  20 . On the contrary, a data signal is output to the outside without passing through the internal buffer when passing through the buffer circuit  3 , so that there is no increase or decrease of cycles, and the data signal passes through the buffer circuit  3  in a zero cycle. 
         [0123]    That is, the value of a latency signal ReqDataLatB from a output of a command signal CmdB to an input/output of a data signal DataB after the passage through the buffer circuit  3  is one cycle smaller than the value of a latency signal ReqDataLatA from a output of a command signal CmdA to an input/output of a data signal DataA before the passage through the buffer circuit  3 . 
         [0124]    Therefore, as shown in  FIG. 8 , a subtracter  21  is inserted in the transfer path of the latency signal ReqDataLatA, and the value indicated by the latency signal is reduced by one, such that the consistency of latency is achieved in the command signals and the data signals before and after the passage through the buffer circuit  3 . 
         [0125]    Furthermore,  FIG. 9  shows an example different from the buffer circuit shown in  FIG. 8 . In the buffer circuit  3  shown in  FIG. 9 , an internal buffer  27  is provided in the transfer path of the data signal. In this case, there is a difference in the method of achieving the consistency of the latency between the write operation and the read operation. 
         [0126]    In the case of the write operation, the internal buffer  27  is provided in the transfer path of the data signal DataA, and the data signal DataA is buffered by the internal buffer  27 , so that a period of one cycle passes. On the other hand, the command signal CmdA passes through the buffer circuit  3  without being buffered, unlike the data signal DataA, so that the command signal CmdA is output to the outside in zero cycle. That is, the value of the latency signal ReqDataLatB from the output of the command signal CmdB to the input of the data signal DataB after the passage through the buffer circuit  3  is one cycle larger than the value of the latency signal ReqDataLatA from the output of the command signal CmdA to the input of the data signal DataA before the passage through the buffer circuit  3 . 
         [0127]    In the read operation, a period of one cycle is needed for the data signal alone, as in the write operation. However, in the read operation, while the command signals Cmd are transferred from the operation modules PE 1 , PE 2  to the memory module  2 , the data signals Data are transferred from the memory module  2  to the operation modules PE 1 , PE 2 , so that there is a difference in signal transfer direction between the command signals and the data signals. 
         [0128]    Therefore, the value of the latency signal ReqDataLatB from the output of the command signal CmdB to the output of the data signal DataB after the passage through the buffer circuit  3  has to be one cycle smaller than the value of the latency signal ReqDataLatA from the output of the command signal CmdA to the output of the data signal DataA before the passage through the buffer circuit  3 . 
         [0129]    Thus, as shown in  FIG. 9 , an adder  24  and a subtracter  25  are provided in the transfer paths of the latency signal within the buffer circuit  3 , so that the value of the input latency signal is increased or decreased by one. The latency signal to which a value has been added by the adder  24  corresponds to the write operation, while the latency signal from which a value has been subtracted by the subtracter  25  corresponds to the read operation. Then, one of the latency signals corresponding to the write operation or the read operation is selected by a multiplexer  26  which uses the command signal CmdA as a selection signal. 
         [0130]    Consequently, the consistency of the latency between the command signal and the data signal is assured for the write operation and the read operation in the data transfer apparatus  1 A. 
         [0131]    In addition, when internal buffers are provided in the respective transfer paths of the command signal and the data signal, the operation is similar to the case where the above-mentioned two configurations are connected in series. Therefore, there is no need for addition and subtraction processing for the latency signal in the case of the write operation, but the value of the latency signal has to be two cycles smaller in the case of the read operation. 
         [0132]    As described above, the buffer circuit  3  shown in  FIG. 8  or  FIG. 9  is used as the buffer circuit  3  for the data transfer apparatus  1 A shown in  FIG. 7 . Thus, the consistency of the latency between the command signal and the data signal in the data transfer apparatus  1 A is assured by the buffer circuit  3  shown in  FIG. 8  and  FIG. 9 . 
         [0133]    Consequently, according to the application of the embodiment of the present invention, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit, and provide a semiconductor integrated circuit of a large scale operating at a high operation frequency. In addition, while the two operation modules PE 1 , PE 2  are shown for simplicity in explanation in the present application, three or more operation modules may be connected to one network. 
         [0134]    (4) Modification 
         [0135]    A modification of the embodiment of the present invention is described with  FIG. 10 . It is to be noted that the same signs are assigned to the same members and such members are not described in detail. 
         [0136]      FIG. 10  shows a data transfer apparatus  1 B in the modification of the embodiment of the present invention. In the configuration of the data transfer apparatus  1  described above, one memory controller MC is connected to the network NW. However, the present invention is not limited to this, and a plurality of memory controllers MC 1 , MC 2  and a plurality of memory modules  2 A,  2 B may be connected to one network NW, as in the data transfer apparatus  1 B shown in  FIG. 10 . 
         [0137]    In the data transfer apparatus  1 B having such a configuration, the latency from the output of a command signal Cmd to the input/output of a data signal may be different for each of the memory controllers MC 1 , MC 2  and each of the memory modules  2 A,  2 B. For example, as shown in  FIG. 10 , a DRAM  2 A and an SRAM  2 B are connected as the memory modules  2 A,  2 B to the memory controllers MC 1 , MC 2 , respectively. Instead of the DRAM  2 A or the SRAM  2 B, a flash memory may be connected to memory controller MC 1 , MC 2 . It is desirable that the latency from the output of the command signal Cmd to the input/output of the data signal Data is large for the data transfer of the DRAM, while it is desirable that the latency from the output of the command signal Cmd to the input/output of the data signal Data is small for the data transfer of the SRAM. As a result, there is a difference between the memory controller MC 1  and the memory controller MC 2  in the values of latency signals required by operation modules PE 1 , PE 2 . 
         [0138]    Therefore, when the third arbitration method is used as the arbitration method of the network NW, the threshold value for the judgment of the arbitration is desirably independently set depending on the latency required by the memory controllers MC 1 , MC 2 . 
         [0139]    In addition, while the two memory controllers MC 1 , MC 2  are shown for simplicity in explanation in the present modification, three or more memory controllers may be connected to one network. 
         [0140]    Furthermore, a plurality of networks may be interposed between the operation modules PE 1 , PE 2  and the memory controllers MC 1 , MC 2 . In this configuration, when the configurations of the plurality of networks are dynamically changed, a signal indicating information on the latency between the memory controller and the plurality of networks may be further added. 
         [0141]    Additionally, while the data transfer apparatus  1 ,  1 A,  1 B using the memory controller MC and the memory module as slave devices has been described in the embodiment of the present invention, the present invention is not limited to this. For example, a hard disk interface may be used instead of the memory controller MC, and a hard disk may be used instead of the memory module  2 . 
         [0142]    As described above, in the modification of the embodiment of the present invention as well, it is possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
       3. Other 
       [0143]    The embodiment of the present invention makes it possible to improve the data transfer efficiency of the semiconductor integrated circuit. 
         [0144]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.