System and method for providing synchronous dynamic random access memory (SDRAM) mode register shadowing in a memory system

A memory system for storing and retrieving data, the memory system comprising:

• one or more ranks of memory devices, each memory device including one or more types of mode registers;
• a memory controller for generating memory commands, the commands including a mode register set command specifying a mode register type and a new mode register setting for memory devices in a specified rank;
• a memory bus in communication with the memory controller;
• and
• a memory hub device comprising:
• an interface to the one or more ranks of memory devices;
• an interface to the memory bus for receiving the commands from the memory controller;
• and
• a mode register shadow module to track settings applied to the mode registers, the module including a shadow register for each type of mode register and a shadow log for each type of mode register, and mode register shadow logic to detect a mode register set command, to store the new mode register setting in the shadow register corresponding to the specified type, and to set one or more bits in the shadow log corresponding to the specified mode register type to indicate which of the ranks of memory devices have been programmed with the new mode register setting.

A memory subsystem comprising:

• one or more ranks of memory devices, each memory device including one or more types of mode registers;
• a memory bus for receiving commands from a memory controller, the commands including a mode register set command specifying a mode register type and a new mode register setting for memory devices in a specified rank;
• a memory hub device comprising:
• an interface to the one or more ranks of memory devices and to the memory bus;
• and
• a mode register shadow module to capture settings applied to the mode registers, the module including a shadow register for each type of mode register and a shadow log for each type of mode register, and mode register shadow logic to detect a mode register set command received on the memory bus, to store the new mode register setting in the shadow register corresponding to the specified mode register type, and to set one or more bits in the shadow log corresponding to the specified mode register type to indicate which of the ranks of memory devices have been programmed with the new mode register setting.