Abstract:
A method is for transferring data from a source target to a destination target in a network. The method includes sending at least one request packet for the destination target, with the request packet containing information relating to a first address where data are located and a second address where data are to be stored. Moreover, at least one transaction request is sent to the source target, with the read request being elaborated from information contained in the request packet. The source target transfers the data located at the first address to the second address.

Description:
FIELD OF THE INVENTION 
     The invention relates, in general, to on-chip communication architectures and is, in particular, directed to the transmission of data from a source target to a destination target belonging to separate interconnection systems of such on-chip communication architectures. 
     BACKGROUND OF THE INVENTION 
     More particularly, the invention is directed to the communication of data between an on-chip bus and a so-called network-on-chip system. As a matter of fact, researchers have recently proposed the network-on-chip concept (NoC) to overcome the limitations relating to the huge efforts necessary to adequately design on-chip communication systems. 
     NoC aims at providing scalable and flexible communication architectures with suitable performance. NoCs are based on a packet switched communication concept and mainly include three NoCs modules, namely a router, a network interface (NI), and a link. 
     Concerning the data format, data packets within a NoC generally include a header and a payload. The header is responsible for carrying all the information required for performing communication, whereas the payload contains the actual information to be transmitted. 
     Conversely, data packets transmitted over an on-chip bus are based on specific transaction protocols. For example, the so-called “ST bus,” developed by the Applicant, is based on a “ST bus protocol type 3” using a separate request channel and a response channel to provide communication between an initiator module and a target module. 
     Conversion of data may be carried out to provide communication between such separate interconnection systems. In addition, when clocks differ, synchronization is to be carried out to allow communication between such interconnection systems. 
     Usually, network interfaces are, in particular, provided to connect communicating blocks of an integrated circuit to the network and between the on-chip bus and the router of the NoC in order to convert data from one packet format to another. 
     In one approach according to the prior art, data communication between two interconnection systems is based on the use of a processing unit associated with a direct memory access (DMA), the processing unit being used as a master unit to send a load request to a source target to retrieve data from a first address. The processing unit also sends a store request to a destination target to store the retrieved data at a destination address, previously stored in the DMA engine. 
     However, such a communication system is limited due to the fact that it is, in general, slow and thus very time consuming. In addition, the processing unit is unavailable during the whole data transfer process. As a matter of fact, a standard DMA engine uses more than one (usually 8) channels. Each channel used for a different DMA transfer and a particular “channel x” is unavailable during a certain DMA transfer related to itself. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, according to one aspect, there is a method for transferring data from a source target to a destination target in a network. 
     The method comprises sending at least one request packet for the destination target, the request packet containing information relating to a first address where data are located and a second address where data are to be stored, sending at least one transaction request from the destination target to the source target, the read request being elaborated from information contained in the request packet, and causing the source target to transfer the data located at the first address to the second address. 
     In other words, according to the prior art, transfer of data is done through a DMA engine in order to move a certain amount of data from one memory starting from a source address to another memory starting from a destination address. The DMA engine starts transferring data to the destination target step by step. 
     Conversely, according to the present approach for transmitting data between the source and destination targets, the network interface to which the destination target is connected sends read requests to the network interface where the source target is connected for reading information from the source target. 
     When the network interface of the destination target receives back the requested information as a reply to the read request, it stores them in the target connected to itself, starting from the destination address. Accordingly, this aspect leads to gain both in terms of performance and processing capabilities for the networks, as the network interfaces are mainly responsible for performing data communication between the source target and the destination target. 
     According to another feature, the request packet contains, in addition, information relating to the size of the transfer. The request packet may also contain information relating to the number of data transfers. 
     One field having information for identifying the method for transferring data may also be included in the request packet. In such a case, the information may be coded in a header field of the request. Concerning the second address, this address may be coded in the header field of the request packet. Conversely, the first address may be coded in the payload of the request packet. In addition, the information relating to the size of the transfer or the information relating to the number of transfers may be coded in the payload of the request packet. 
     For example, the method may comprise checking the information for identifying the method for transferring data, retrieving from the header field the second address where data is to be stored, storing in memory means or circuitry the second address, and retrieving the first address where data are located, the number of transfers, and the transfer size, from the payload. 
     The method may further comprise storing in memory means or circuitry of the network interface connected to the destination target request packets, each specifying at least one address where a set of data is to be retrieved. 
     For example, the transaction requests are incrementally sent from the network interface connected to the destination target to a network interface connected to the source target. In addition, the location of the source target may be retrieved from a look-up table used for decoding the first address. 
     According to another aspect, there is a network interface for connecting and providing communication in a network between a source target and a destination target, comprising means or circuitry for retrieving, in at least a request packet, information relating to a first address where data to be received is located, and to a second address where data is to be stored and means or circuitry for causing the source target to transfer the data located at the first address to the second address. 
     This network interface may further comprise decoding means or circuitry for decoding a header of the request packet for retrieving the second address and for decoding a payload of the request for retrieving the first address According to another feature of the network interface, there are means or circuitry for decoding the payload of the request packet to retrieve a size of data transfer and a number of data transfers. 
     For example, the network interface further comprises first memory means or circuitry for storing transaction requests elaborated from information data retrieved from the request packet and means or circuitry for incrementally sending the transaction requests to the source target. The network interface may further comprise second memory means or circuitry for storing data transmitted by the request. 
     In one embodiment, the network interface comprises a first part for performing a data protocol conversion and a second part for performing protocol independent data processing. For example, the first and second parts each comprise an input control block and an output control block for extracting request data in a first format from incoming request packets and storing the extracted data in the second memory means or circuitry, and for reading contents from the second memory means or circuitry and for generating the read data signals in a second format. The network interface may further comprise means or circuitry for synchronizing the input and output control blocks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features of the invention will appear on examining the detailed description of embodiments, these being in no way limiting, and of the appended drawings in which 
         FIG. 1  illustrates schematically the architecture of a network interface implemented for providing communication between a network-on-chip and an on-chip bus, in accordance with the present invention; 
         FIG. 2  shows a generic architecture of the network interface of  FIG. 1 ; 
         FIG. 3  shows the structure of a request packet header, in accordance with the present invention; 
         FIG. 4  illustrates the structure of a request packet payload, in accordance with the present invention; 
         FIG. 5  illustrates a detailed description of the network interface architecture, in accordance with the present invention; and 
         FIG. 6  illustrates the transfer of transaction requests and of responses from a distributed DMA engine to the destination target and then to the source target, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the embodiment illustrated in  FIG. 1 , the network interface NI is intended to provide communication between two separate interconnected systems namely, in the illustrated example, a network-on-chip and an on-chip bus. 
     More particularly, this network interface is used to transfer data from a source target connected to a network on-chip to a destination target connected to an on-chip bus. However, it should be noted that the network interface can be used to allow communication between other types of interconnection systems and, in particular, it can be used with other on-chip protocols, namely the so-called Advanced Microcontroller Bus Architecture (AMBA), Advanced eXtensible Interface (AXI), and Open Core Protocol (OCP) protocols. 
     As it is known, data transmitted through the network on-chip and through the on-chip bus have differing formats. As a matter of fact, network on-chip is a communication architecture for systems on-chip, usually based on the concept of packet switching rather than circuit switching. 
     In an on-chip bus, data is transmitted in the form of packets including a set of cells that are not interruptible. In a NoC context, the packets are split into basic units called flits (Flow Control Units), and comprise a payload containing actual information to be transmitted and a header responsible for carrying all the information required for performing communication. 
     In view of the foregoing, the network interface NI is intended to provide communication between and transmit response packets to a source target, connected to the network through a router, and a destination target, connected to the on-chip bus. 
     The network interface is thus intended to realize a conversion of request packets, according to the protocol supported by the on-chip bus, into request packets having the structure corresponding to the network on-chip concept. In addition, the network interface is intended to convert response packets issued from the NoC into packets corresponding to the on-chip bus. 
     In addition, the network interface is intended to allow communication between a destination target and a source target, taking into account possible clock differences. Although one network interface has been illustrated, the communication system is based on a distributed Direct Memory Access concept (distributed DMA) used in systems having a unique master and several targets, in which the master acts as a DMA initiator, and is responsible for programming transfers of data between the targets connected. 
     As a matter of fact, the DMA initiator, namely a DMA engine, instructs the network interface where the destination target is connected, to send to the network interface where the source target is connected a read request for a set of bytes starting from an address a in the source target. When the destination target network interface receives back these bytes as a reply to the read request, it stores them in the target connected to itself, starting from the address β. Once finished, the destination target network interface propagates to the DMA engine a reply in order to signal the end of this DMA transfer. 
     In other words, the DMA initiator engine sends particular request instructions in the form of “$ load α store β” to the network interface where the destination target is connected, meaning that $ bytes starting from the address α at the source target should be transferred to the destination target from address β. This shows that all communicating blocks can be either a destination target or a source target of a DMA transfer, these targets being connected to the network on-chip with the distributed DMA network interface of  FIG. 1 , while the DMA engine initiator is connected to the network with an initiator network interface. 
     As illustrated in  FIG. 2 , the distributed DMA network interface comprises two blocks, namely a first protocol dependent module  1 , and a second protocol independent module  2 , having a target module and a master module. 
     The first module is responsible for performing the transformation required between the on-chip bus protocol and the NoC packets for normal transactions, and, to cope with the management of the master and the target module  2 , in order to cope with the distributed DMA transfers. The second module  2  is responsible for what is protocol independent, for example internal storage and communication with the routers. 
     As illustrated, the first module  1  communicates with the on-chip bus using bus packets corresponding to the format used in the on-chip bus, whereas the second module communicates with routers R and R′ using network layer packets having, as previously indicated, a header H and a Payload. 
     To cope with the above mentioned special DMA transfer in which the DMA transfer functions are spread within the network interfaces, the initiator engine of the distributed DMA request provides the starting local address a where to store the transferred data, the starting remote address β where the data is located, and the size of the transfer. This information is coded, inside the NI initiator  15  in  FIG. 6 , within the request packet and is sent to the network interface where the destination target is connected. 
     For that purpose, the DMA request packet is tagged so that the network interface can detect the distributed DMA request. For example, as illustrated in  FIG. 3 , single bytes are used to transmit the requested information. However, it should be noted that the DMA request made by the so called “distributed DMA engine” is not tagged whereas the DMA request packet related to this DMA request and produced by the initiator NI ( 15   FIG. 6 ) is tagged. 
     In particular, as illustrated, the bit &lt; 23 &gt;in the request packet header is set to one by the initiator network interface connected to the distributed DMA engine. The DMA engine initiator uses a specific operation code (opcode) in order to code the distributed DMA request. For example, in a specific embodiment, in the above-mentioned STBus type 3 protocol a possible opcode to be used is 0 011 0110, where opcode &lt; 7 &gt;=0 and where opcode&lt; 6 : 4 &gt;=0 11 to indicate the size of the transaction, namely eight bytes, in this case, and opcode &lt; 3 : 0 &gt;=0110, to indicate, in comparison with a standard store opcode 0010, that the byte opcode &lt; 2 &gt;has been set to one and is used to signal advanced transaction. 
     Moreover, header&lt; 35 : 28 &gt;is used to indicate the DMA initiator source and header&lt; 39 : 36 &gt; is used to identify the DMA transaction. Additionally, header&lt; 71 : 40 &gt;is used to code the destination address β for the DMA transfer. 
     The illustrated structure shows that the DMA initiator gives the destination address β of the DMA transfer using the header field of the request packet. The remote address where the data to be transferred is located and the size in bytes of the transfer are coded within the payload field of the request packets. 
     As indicated in  FIG. 4 , the payload field &lt; 31 : 0 &gt; indicates the remote address where the data is to be retrieved, the payload field &lt; 35 : 32 &gt; indicates the number of transfers to be carried out, and the payload field &lt; 38 : 36 &gt; indicates the transfer size. 
     In other words, the DMA initiator, using information coded within the request packet, instructs the distributed DMA network interface connected to the destination target about the way to gather the data to be transferred from the source target. In other words, the distributed DMA engine produces a request of memory transfer, that once filtered by the initiator NI ( 15   FIG. 6 ) has as result the request packet related to the wanted distributed DMA. 
     As indicated further, the destination network interface stores in memory means or circuitry a set of load requests, the number of which corresponds to the number of transfers. Each request is intended to retrieve a set of data from the source target, the number of bytes corresponding to the transfer size coded within the payload. 
     In addition, the DMA engine initiator may instruct the destination network interface if the load requests may be linked inside a chunk, namely a set of packets linked together by a lock signal. It should be noted that the number of transfers coded within the payload field is, for example, coded in four bits such that it is possible to have from one to sixteen transfers relative to a single “distributed DMA” transaction. The transfer size information is instead coded, for example, using three bits such that the variable transfer size lies between 2 and 64 bytes (power of 2 of the value of these 3 bits). Accordingly, the biggest DMA transfer available is 16×64, namely 1024 bytes. 
     Reference is now made to  FIG. 5  illustrating an example of a detailed architecture of a DMA network interface. As illustrated, the network interface comprises a first part, namely the first dependent protocol module  1 , and a second part, namely the above mentioned independent protocol module  2  having a target module and a master module. 
     When data is transmitted from the on-chip bus through the bus interface to the NoC, the first module encodes traffic from the bus and stores it inside a First-In First-Out (FIFO) memory  4 . In other words, the first module realizes a conversion of the received traffic to generate a header and a payload according to the NoC requirements and store them in the FIFO  4 . The target module reads contents from the memory  4  and sends them by flits to the NoC, through the router R. 
     When data is transferred from the NoC to the bus, the second module  2  collects flits from the NoC side, realizes a packet reconstruction, and puts the collected packets in a corresponding FIFO memory  5 . The first module  1  thus reads the FIFO and decodes its content in order to extract the correct bus traffic. 
     It should be noted that the FIFO memories  4  and  5  are provided within the network interface in order to decouple the first module from the second module, meaning that several packets can be stored inside FIFOs by the first module before being sent. In addition, this choice leads to gain both in terms of performance and in terms of memory usage. 
     The description of the overall architecture of an example of a network interface will now be made in reference to an embodiment in which a transmission request is transmitted from a network interface connected to the network on-chip, to a source target network interface connected to the bus on-chip. However, the description also applies in the case in which the request is issued from a destination target connected to the bus in order to retrieve and store data stored in a source target connected to the NoC. 
     As illustrated, the first module, the target module, and the master module each comprise an input control block  6   a,    6   b  and  6   c  and an output control block  7   a,    7   b  and  7   c.  When the request packet is received by the input control block  6   a  of the target module, the packets, split into flits, are collected by the input control block  6   a,  are reconstructed, and are saved inside the FIFO memory  5  in the proper order. 
     The output control block  7   b  of the first module is thus responsible for taking the packet saved in the FIFO memory  5  and to produce the request for the source target according to the on-chip bus protocol. 
     It should be noted that, as the output control block  7   b  and the input control block  6   a  may operate at different frequencies, a synchronization block  8  is provided between the two blocks  6   a  and  7   b  in order to avoid metastability problems in exchanging signals used by the two blocks to correctly evaluate the full or empty status of the memory  5 . 
     In addition, as already indicated, the DMA request packet can be identified by receiving distributed DMA Nis, by checking a DMA tag ( FIG. 3 ) in the transport header of the request packet. When the output control block  7   b  has checked that the header field &lt; 23 &gt; is set to one, it stores in an internal buffer some of the information coming with the request packet and stored in the FIFO memory  5 , namely a DMA initiator source identifier and the local address β where the data once retrieved may be stored, and the transaction identifier given by the DMA engine initiator in order to make a distinction among multiple outstanding DMA requests. 
     In addition, from the first four bytes of the payload in the DMA request packet, the output control block  7   b  retrieves the remote address a of the source target containing the data which may be transferred locally to the destination target. Furthermore, from the fifth byte inside the payload, the output control block retrieves the number of transfers and the transfer size information. 
     The output control block  7   b  then stores, in a FIFO memory  9  of the master module, N request transactions of the read type, for example N read transactions in the form “read TS”, where N and TS respectively correspond to the number of transfers and to the transfer size. These read TS requests are incrementally addressed to the remote source target, starting from the remote address a. Accordingly, each read TS request has a different incremental address α+ITS in which I varies from zero to N−1. 
     It should be noted that these read transactions are mapped in the NoC packets in the same way as if they were produced by an initiator network interface connected to an external master block such as a central processing unit (CPU) or similar. It should also be noted that the network interface, and in particular the network interface of the destination target, comprises a look-up table for decoding the remote address α. 
     The read transaction TS requests extracted from the FIFO memory  9  ate then converted into packets split into flits by the output control block  7   c  and are then forwarded to the source target. 
     N read transaction requests are emitted. An internal counter C provided, for example, within the output control block  7   b,  is used to check how many read transaction requests are completed. The value of the counter initially set to N is decremented when a read transaction request is completed, each time a result of a read transaction is gathered from FIFO  10  and transformed to a write request towards the destination. 
     Each write request has thus a different incremental address in the form β+(N−C)×TS. In other words, these are the store requests (namely N write transactions TS) emitted towards the destination target once the Read TS results have been gathered. 
     A similar counter RC initially set to 1 is also provided, for example in the input control block  6   b,  to check how many response packets are received in reply to the write requests. This counter RC is also decremented when such a response packed is received. 
     When the value of the counter C is zero, this indicates that the read TS transactions have been propagated to the source target, read TS results are arrived in FIFO  10  and are used to produce write requests. 
     Concerning the counter RC of the input control block  6   b,  when the value of this counter is not zero, if the input control block receives a response from the target, it may determine that the reply is the response to the transaction. If the counter value is bigger than one, meaning that transaction requests are still pending, in this case, the RC counter is decremented and this response is skipped. If, instead, the RC value is one, the last reply of the last write transaction request related to a distributed DMA has been received. In this case, the input control block  6   b  stores the response coming from the target in order to produce a response for the overall memory transfer to the distributed DMA engine. 
     As illustrated in  FIG. 5 , when received, the response packets split into flits are reconstructed by the input control block  6   c  and stored in a FIFO memory  10  associated with the control block  6   c.  This phrase is relative to the first N read TS transactions responses. The stored packets are then retrieved by the output control block  7   b  of the first module for generating signals according to the format supported by the on-chip bus and delivered to the destination target. 
     A similar approach is used to transmit data from the on-chip bus to the NoC. In this case, the received packets are processed by the input control block  6   b  for header and payload generation and are then stored in the FIFO memory  4 . The data is then retrieved by the output control block  7   a  for packet generation according to the format supported by the NoC and are then forwarded to the NoC. 
     At last, it should be noted that other synchronization blocks, such as  11 ,  12  and  13  are used to synchronize the input control block  6   c  and the output control block  7   b  and  7   c,  as well as the input and output control blocks  6   b  and  7   a.    
     Referring now to  FIG. 6 , an example of the path of the request DMA packets from a DMA engine  14  to a proper DMA network interface is given. 
     As previously indicated, the DMA request issued by the distributed DMA engine (arrow A 1 ) is transmitted to the DMA engine network  15  interface that produces a DMA request packet that is then delivered to the proper network interface of the destination target (arrow A 2 ). 
     As also previously indicated, incoming data transmitted by the request is retrieved and stored within the FIFO memory of the network interface and then decoded by the output control block of the corresponding first module. 
     The N request transaction requests of the type “read TS” are then stored in the FIFO memory  9  of the corresponding master module (arrows A 3  and A 4 ) and then transmitted to the source target NI  17  (arrow A 5 ) and to the target  19  (arrows A 6  and A 7 ). Data is then retrieved by the network interface  17  connected to the network and, in particular, by the input control block  6   b,  to be transmitted, through the output control block  7   a  of the target module  2 , to the input control block  6   c  of the master module of the network interface connected to the destination target (arrows A 8 , A 9  and A 10 ). After packet reconstruction and storage of the packets in the FIFO memory  10  ( FIG. 5 ), the retrieved data is transmitted to the destination target  18  using N write TS transactions (arrows A 11  and A 12 ) 
     Thereafter, N−1 responses to the first N−1 write TS transactions are transmitted to the target module (arrows A 13  and A 14 ). The last response, namely the Nth one, is the one that is used as a response for the DMA request and reaches the DMA initiator  14  (arrows A 15  and A 16 ).