Full access to memory interfaces via remote request

• US 7,290,096 B2
• Filed: 04/13/2006
• Issued: 10/30/2007
• Est. Priority Date: 01/14/2003
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Marshall, John W., Scott, Jeffery B., Jeter, Robert E. Jr.
• Primary Examiner(s): Thai; Tuan V.
• Application Number:
  US11/403,364
• Publication Number:
  US 20060184753A1
• Time in Patent Office: 565 Days
• Field of Search: 711/100, 711/118, 711/154, 711/167, 709/213, 709/223, 709/230
• US Class Current: 711/154
• CPC Class Codes: G06F 12/0284 Multiple user address space allocation, e.g. using different base addresses interprocessor communication G06F15/163
• CPC Class Codes: G06F 12/1072 Decentralised address translation, e.g. in distributed shared memory systems
• CPC Class Codes: H04L 67/56 Provisioning of proxy services store-and-forward switching systems in data switching networks H04L12/54
• CPC Class Codes: H04L 67/59 Providing operational support to end devices by off-loading in the network or by emulation, e.g. when they are unavailable

Abstract

A system and method for enabling a processor to access a memory not directly coupled to the processor. A memory request, including a request identifier field, is issued by a processor to a local memory management unit (MMU). Using the request identifier field, the local MMU determines whether the memory request should be issued by the local memory management unit (MMU) to a local memory, or should be transferred by the local MMU to a remote MMU and issued by the remote MMU to a remote memory, the remote memory associated with a different processor. In this manner, the remote MMU issues certain memory requests on behalf of the local processor and returns any results back to the local processor.

Claims

1. A memory request stored in a computer readable medium, the memory request used by a local processor to access a remote memory that is not directly coupled to the local processor, the memory request comprising:

a memory operation field configured to specify that a memory operation to be performed;

a memory address field configured to specify a memory location on which the memory operation is to be performed; and

a request identifier (ID) field configured to specify whether the memory request is to be issued by a local memory management unit (MMU) to a local memory associated with the local processor, or is to be transferred by the local MMU to a remote MMU and issued by the remote MMU to the remote memory, the remote memory associated with a processor other than the local processor.

2. The memory request of claim 1 wherein the request ID field further comprises:

a register (REG) identifier (ID) field configured to designate an MMU register to store data associated with the memory request.

3. The memory request of claim 1 wherein the request ID field further comprises:

a remote request (REM) field configured to designate a specific MMU for issuing the memory request.

4. The memory request of claim 1 wherein the a memory operation field is further configured to specify that the memory operation is a read operation, and wherein the memory request causes data to be read from the remote memory by the remote MMU and to be transferred from the remote MMU to the local MMU, for use thereafter by the local processor.

5. The memory request of claim 1 wherein the a memory operation field is further configured to specify that the memory operation is a write operation, and wherein the memory request causes data to be transferred from the local MMU to the remote MMU and to be written by the remote MMU to the remote memory.

6. A method for a local processor to access a remote memory that is not directly coupled to the local processor, the method comprising the steps of

configuring a memory operation field of a memory request to specify a memory operation to be performed;

configuring a memory address field of the memory request to specify a memory location on which the memory operation is to be performed; and

configuring a request identifier (ID) field of the memory request to specify whether the memory request is to be issued by a local memory management unit (MMU) to a local memory associated with the local processor, or is to be transferred by the local MMU to a remote MMU and issued by the remote MMU to the remote memory, the remote memory associated with a processor other than the local processor.

7. The method of claim 6 wherein the step of configuring a request identifier (ID) field further comprises the step of:

configuring a register (REG) identifier (ID) field to designate an MMU register to store data associated with the memory request.

8. The method of claim 6 wherein the step of configuring a request identifier (ID) field further comprises the step of:

configuring a remote request (REM) field to designate a specific MMU associated with the memory request.

9. The method of claim 6 wherein the remote MMU is coupled to the remote memory, the local MMU is coupled to the local memory, and the local MMU is couple to the remote MMU.

10. The method of claim 6 further comprising the steps of:

sending the memory request by the local processor to the local MMU; and

determining, by the local MMU, whether to issue the memory request to the local memory or to transfer the memory request to the remote MMU, in response to the request ID field.

11. The method of claim 10 further comprising the steps of:

determining, by the remote MMU, if remote memory requests are enabled; and

if remote memory requests are not enabled, stalling the memory request at the remote MMU until remote memory requests are enabled.

12. The method of claim 11 wherein the step of determining if remote memory requests are enabled further comprises the step of:

reading the contents of a control register of the remote MMU, the control register storing an indicator for remote memory requests.

13. The method of claim 10 further comprising the step of:

determining, by the remote MMU, if remote memory requests are enabled; and

if remote memory requests are enabled, transferring the memory request to an arbiter of the remote MMU.

14. The method of claim 13 further comprising the step of:

issuing the memory request at a time determined by the arbiter, the arbiter giving preference to memory requests received from processors coupled directly to the remote MMU over memory requests received from other MMUs.

15. The method of claim 6 wherein the memory operation field specifies that the memory operation is a read operation, and the method further comprises the steps of:

reading data from the remote memory by the remote MMU;

transferring the data from the remote MMU to the local MMU; and

storing the data in a register of the local MMU, the register accessible by the local processor.

16. The method of claim 6 wherein the memory operation field specifies that the memory operation to is a write operation, and the method further comprises the steps of:

transferring the data to be written to the remote memory from the local MMU to the remote MMU;

storing the data in a register of the remote MMU; and

writing, by the remote MMU, the data to the remote memory.

17. A memory request stored in a computer readable medium, the memory request used by a local processor to access a remote memory that is not directly coupled to the local processor, the memory request comprising:

means for specifying a memory operation to be performed;

means for specifying a memory location on which the memory operation is to be performed; and

means for specifying whether the memory request is to be issued by a local memory management unit (MMU) to a local memory associated with the local processor, or is to be transferred by the local MMU to a remote MMU and issued by the remote MMU to the remote memory, the remote memory associated with a processor other than the local processor.

18. The memory request of claim 17 further comprising:

means for designating an MMU register to store data associated with the memory request.

19. The memory request of claim 17 further comprising:

means for designating a specific MMU for issuing the memory request.

20. The memory request of claim 17 wherein the means for specifying a memory operation to be performed specify that the memory operation is a read operation, and wherein the memory request causes data to be read from the remote memory by the remote MMU and to be transferred from the remote MMU to the local MMU, for use thereafter by the local processor.

21. The memory request of claim 17 wherein the means for specifying a memory operation to be performed specify that the memory operation is a write operation, and wherein the memory request causes data to be transferred from the local MMU to the remote MMU and to be written by the remote MMU to the remote memory.

22. A method for a first processor to access a remote memory that is not directly coupled to the first processor to prefetch data for use by a second processor, the method comprising the steps of:

sending the memory request by the first processor to a first memory management unit (MMU) coupled to the first processor;

transmitting the memory request by the first MMU unit to a second MMU, the second MMU coupled to both the second processor and to an external memory associated with the second processor;

issuing the memory request by the second MMU to the external memory;

storing data returned in response to the memory request in one or more registers of the second MMU, such that the data will be available to the second processor absent additional accesses to the external memory.

23. The method of claim 22 wherein the memory request includes a memory operation field configured to specify that a read operation is to be performed, a memory address field configured to specify a memory location from which to read, and a request identifier (ID) field configured to specify that the memory request is to be issued by the second MMU.