Multiple processor system and method including multiple memory hub modules
A processor-based electronic system includes several memory modules arranged in first and second ranks. The memory modules in the first rank are directly accessed by any of several processors, and the memory modules in the second rank are accessed by the processors through the memory modules in the first rank. The data bandwidth between the processors and the memory modules in the second rank is varied by varying the number of memory modules in the first rank that are used to access the memory module in the second set. Each of the memory modules includes several memory devices coupled to a memory hub. The memory hub includes a memory controller coupled to each memory device, a link interface coupled to a respective processor or memory module, and a cross bar switch coupling any of the memory controllers to any of the link interfaces.
1. A memory module, comprising:
a plurality of memory devices; and
a memory hub comprising:
a plurality of memory controllers, each of the memory controllers being coupled to at least one of the memory devices in the memory module; and
a switch having a plurality of first switch ports respectively coupled to a plurality of memory requesters, a plurality of second switch ports each being coupled to a respective one of a plurality of third switch ports external to the memory module, and a plurality of memory ports coupled to respective ones of the memory controllers,
wherein, in response to output from a corresponding one of the memory requesters, the switch is configured to selectively couple the first switch receiving the output from the corresponding memory requester to either: one of the third switch ports or one of the memory ports.
2. The memory module of claim 1 wherein each of the memory devices comprises a dynamic random access memory device.
3. The memory module of claim 1 wherein each of the memory hubs further comprises a respective cache memory device associated with each of the memory controllers, each of the cache memory devices being operable to store data that is accessed through a respective one of the memory ports of the switch.
4. The memory module of claim 1 wherein the memory controllers and the switch are fabricated as a common integrated circuit in a semiconductor substrate.
5. The memory module of claim 1 wherein the memory devices and the memory hub are fabricated as a common integrated circuit in a semiconductor substrate.
6. The memory module of claim 1 wherein the memory hub further comprises a respective write buffer associated with each of the memory controllers, each of the write buffers being configured to receive write data and associated write addresses through a respective one of the memory ports of the switch and to store the write data and addresses for subsequent coupling to a respective one of the memory controllers.
7. The memory module of claim 6 wherein each of the write buffers is configured to accumulate write data and addresses for a plurality of write memory accesses and to then sequentially couple the plurality of write data and addresses to a respective one of the memory controllers without any intervening read memory accesses.
8. The memory module of claim 1 wherein each of the memory hubs further comprises a direct memory access device coupled to the switch and the memory controllers, the direct memory access device being configured to cause the switch and each of the memory controllers to perform memory write and read accesses.