Patent Application
20050055478
1. Field of the Invention
The invention relates generally to a direct memory access and, more particularly, to using one processor to set up a direct memory access for another processor.
2. Description of the Related Art
In a computer system, data is transferred from one memory location to another memory location using load and store instructions or using direct memory access controller (DMAC). Load and store instructions have a very long latency. That is, a processor in the computer system should wait for a large amount of data to transfer before working on the load and store instruction. At first, data needs to be read from one memory location into a processor's registers. Then, the data will be transmitted to another memory location from the processor's registers.
DMAC provides a mechanism to move data from a memory location to another memory location without involvement of a processor. In a prior art system, the processor has to set up the DMAC before the DMAC can perform the data transfer on its own. Once the DMAC is set up, the processor can perform other tasks while the DMAC takes care of the data transfer.
A multi-processor system may have one or more special processors dedicated to important tasks and one or more general-purpose processors. In such a multi-processor system, a special processor may have its own DMAC to set up. In that case, the special processor ends up spending its valuable time on setting up the DMAC. This may adversely affect the entire performance of the multi-processor system, because the special processor cannot perform its own special tasks while it is setting up the DMAC.
Therefore, a need exists for a system and method for improving performance of a computer system by freeing particular processor(s) from the job of setting up the DMAC.
The present invention provides a system and method for setting up a direct memory access for a first processor. The system includes a first processor and a local memory. The local memory is coupled to the first processor. A first direct memory access controller (DMAC) is coupled to the first processor and the local memory. A system memory is in communication with the first DMAC. A second processor is in communication with the first DMAC such that the second processor sets up the first DMAC to handle data transfer between the local memory and the system memory. The second processor is interrupted when the first DMAC finishes handling the data transfer.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail.
It is further noted that, unless indicated otherwise, all functions described herein may be performed in either hardware or software, or some combination thereof. In a preferred embodiment, however, the functions are performed by a processor such as a computer or an electronic data processor in accordance with code such as computer program code, software, and/or integrated circuits that are coded to perform such functions, unless indicated otherwise.
Referring to
The first processor 102 is coupled to the local memory 104 via a connection 122. The first processor 102 is also coupled to the DMAC 108 via a connection 124. The first processor 102 is also coupled to the proxy DMAC 110 via a connection 126. The local memory is coupled to the proxy DMAC via a connection 128.
The DMAC is coupled to the first bus controller 114 via a connection 130. The proxy DMAC 110 is coupled to the first bus controller 114 via a connection 132. The first bus controller 114 is coupled to the system bus 118 via a connection 134. The system bus 118 is coupled to the system memory 120 via a connection 136. The system bus 118 is coupled to the second bus controller 116 via a connection 138. The second bus controller 116 is coupled to the MMIO access controller 112 via a connection 140. The MMIO access controller 112 is coupled to the second processor 106 via a connection 142.
Preferably, the first processor 102 is a special processor, whereas the second processor 106 is a general-purpose processor. Also, the computer system 100 may be generalized to have a plurality of general-purpose processors. In that case, an additional cache (not shown) and an additional bus controller (not shown) may be coupled between each additional processor (not shown) and the system bus 118 in a manner similar to the connection between the second processor 106 and the system bus 118.
The first processor 102 is configured to specifically work with the local memory 104. In other words, the local memory 104 is dedicated to the first processor 102. Note that the local memory 104 is an example of a working memory space of the first processor 102. Therefore, different configurations of such a working memory space may be used for the first processor 102 without departing from the true spirit of the present invention. For example, such a working memory space may comprise a plurality of local memories.
Preferably, the first processor 102 is a special processor that primarily or exclusively performs special tasks with the help of the local memory 104. When the first processor 102 needs to access certain data to perform one of the special tasks, in one situation, the data may not be available from the local memory 104 but from the system memory 120. In another situation, the first processor 102 has just performed a special task and has to store certain output data in the local memory 104. Sometimes, this output data should be transmitted to the system memory 120 in order to make the data available to other processors, such as the second processor 106.
In these and other applicable situations, the second processor 106 is configured to set up the proxy DMAC 110 to perform the data transfer between the local memory 104 and the system memory 120. By this configuration, the first processor 102 does not have to spend any of its time in setting up the DMAC 108 for such data transfer between the local memory 104 and the system memory 120.
The second processor 106 loads a load signal (not shown) from the proxy DMAC 110 to determine whether the proxy DMAC 110 is ready to be set up for the first processor 102. Preferably, the second processor 106 analyzes the load signal to make the determination. Specifically, the proxy DMAC 110 transmits the load signal to the first bus controller 114 via the connection 132. The first bus controller 114 transmits the load signal to the system bus 118 via the connection 134. The system bus 118 transmits the load signal to the second bus controller 116 via the connection 138. The second bus controller 116 transmits the load signal to the second processor 106 either directly or through the MMIO access controller 142.
If it is determined that the proxy DMAC 110 is ready to be set up for the first processor 102, the first processor 102 sets up the proxy DMAC 110 by sending an access request (not shown) to the proxy DMAC 110. Specifically, the second processor 106 transmits the access request to the MMIO access controller 112 via the connection 142. The MMIO access controller 112 transmits the access request to the second bus controller 116 via the connection 140. Optionally, the MMIO access controller 112 may be skipped. The second bus controller 116 then transmits the access request to the system bus 118 via the connection 138. The system bus transmits the access request to the first bus controller 114 via the connection 134. The first bus controller 114 then transmits the access request to the proxy DMAC 110 via the connection 132.
Once the proxy DMAC 110 receives the access request, the proxy DMAC 110 is set up to handle any data transfer between the local memory 104 and the system memory 120 without interrupting the first processor 102 or the second processor 106.
When the first processor 102 requests data transfer from the system memory 120 to the local memory 104, the proxy DMAC 110 sends a data transfer request (not shown) to the system memory 120. In response to the data transfer request, the system memory 120 sends requested data back to the proxy DMAC 110. The proxy DMAC 110 then sends the requested data to the local memory 104. Specifically, the proxy DMAC 110 first transmits the data transfer request to the first bus controller 114 via the connection 132. The first bus controller 114 then transmits the data transfer request to the system bus 118 via the connection 134. The system bus 134 then transmits the data transfer request to the system memory 120 via the connection 136. In response to the data transfer request, the system memory 120 transmits the requested data first to the system bus 118 via the connection 136. The system bus 118 then transmits the requested data to the first bus controller 114 via the connection 134. The first bus controller 114 then transmits the requested data to the proxy DMAC 110 via the connection 132. The proxy DMAC 110 then transmits the requested data to the local memory 104.
When the requested data is stored in the local memory 104, the proxy DMAC 110 notifies the first processor that the data transfer is complete, preferably by sending a signal to the first processor 102 via the connection 126. Upon being notified of the completion of the data transfer, the first processor 102 accesses the local memory 104 to perform certain tasks on the requested data and generates output data. Sometimes, this output data has to be made available to other processors (e.g., the second processor 106) than the first processor 102. In this situation, the output data has to be stored in the system memory 120 for such other processors to access the output data. This requires that the output data be copied or moved from the local memory 104 to the system memory 120. Therefore, the proxy DMAC 110 sends the output data from the local memory 104 to the system memory 120.
Generally, the proxy DMAC 110 sends the local memory 104 a data transfer request for the output data. In response to this data transfer request, the local memory 104 sends the output data to the proxy DMAC 110. The proxy DMAC 110 then sends the output data to the system memory 120. Specifically, the proxy DMAC 110 transmits the output data first to the first bus controller 114 via the connection 132. The first bus controller 114 then transmits the output data to the system bus 118 via the connection 134. The system bus 118 then transmits the output data to the system memory 120 via the connection 136.
Optionally, the first processor 102 may be able to set up the DMAC 108 on some occasions without the help of the second processor 106. On such occasions, the DMAC 108 may be directly coupled to the local memory 104 via a connection (not shown) to handle the data transfer between the local memory 104 and the system memory 120 once the DMAC 108 is set up.
In an alternative embodiment, the DMAC 108 and the proxy DMAC 110 may be put together within a combined DMAC (not shown) such that the combined DMAC contains both the DMAC 108 and the proxy DMAC 110. In this manner, a single connection (not shown) may be used between the combined DMAC and the local memory 104. Similarly, a single connection (not shown) may be used between the combined DMAC and the first bus controller 114. In this alternative embodiment, either the first processor 102 or the second processor 106 may set up the combined DMAC depending on the availability of the first processor 102 and overall performance of the computer system 100.
In another alternative embodiment, the proxy DMAC 110 may be configured to be set up by either the first processor 102 or the second processor 106, depending on the availability of the first processor 102 and overall performance of the computer system 100. In this alternative embodiment, the DMAC 108 is not used.
Now referring to
In step 204, the load signal is analyzed. Preferably, the second processor 106 analyzes the load signal. In step 206, it is determined whether the DMAC is ready to be set up for handling data transfer for the first processor. Preferably, the second processor 106 determines whether the proxy DMAC 110 is ready to be set up for handling data transfer for the first processor 102 between the local memory 104 and the system memory 120. If it is determined in step 204 that the DMAC is not ready to be set up for handling data transfer for the first processor, the routine goes to step 202.
In step 208, upon a determination that the DMAC is ready to be set up for handling data transfer for the first processor, an access request is transmitted from the second processor to the DMAC to set up the DMAC for the data transfer. Preferably, the access request is transmitted from the second processor 106 to the proxy DMAC 110 to set up the proxy DMAC 110 for the data transfer between the local memory 104 and the system memory 120.
It will be understood from the foregoing description that various modifications and changes may be made in the preferred embodiment of the present invention without departing from its true spirit. This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be limited only by the language of the following claims.
