Apparatus and method for data bypass for a bi-directional data bus in a hub-based memory sub-system

• US 8,291,173 B2
• Filed: 07/20/2010
• Issued: 10/16/2012
• Est. Priority Date: 02/05/2004
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Larson, Douglas A., Cronin, Jeffrey J.
• Primary Examiner(s): DOAN, DUC T
• Application Number:
  US12/840,007
• Publication Number:
  US 20100287323A1
• Time in Patent Office: 819 Days
• Field of Search: None
• US Class Current: 711/138
• CPC Class Codes: G06F 12/0888 using selective caching, e.g. bypass
• CPC Class Codes: G06F 13/161 with latency improvement
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence

Abstract

A memory hub includes first and second link interfaces for coupling to respective data busses, a data path coupled to the first and second link interfaces and through which data is transferred between the first and second link interfaces, and further includes a write bypass circuit coupled to the data path to couple write data on the data path and temporarily store the write data to allow read data to be transferred through the data path while the write data is temporarily stored. A method for writing data to a memory location in a memory system is provided which includes accessing read data in the memory system, providing write data to the memory system, and coupling the write data to a register for temporary storage. The write data is recoupled to the memory bus and written to the memory location following provision of the read data.

Claims

1. A logic device, comprising:

first and second data bus interfaces configured to be coupled to a bidirectional data bus,

the bidirectional data bus configured to transfer read data in a first direction between the first and second bus interfaces and to transfer write data in a second direction opposite of the first direction between the first and second bus interfaces; and

a bypass circuit coupled to the first and second data bus interfaces and configured to store write data from the bidirectional data bus to transfer the write data from the first data bus interface to the second data bus interface in the second direction instead of over the bidirectional data bus to allow read data to be transferred on the bidirectional data bus from the second data bus interface to the first data bus interface in the first direction, the bypass circuit further configured to restore stored write data to the bidirectional data bus to complete the transfer of the write data,

wherein the bypass circuit is configured to be controlled responsive to a bypass signal.

2. The logic device of claim 1 wherein the bypass circuit comprises:

a first buffer having an input and an output, the input configured to be coupled to the bidirectional bus;

a register having an input configured to be coupled to the output of the first buffer and further having an output;

a multiplexer having a first input configured to be coupled to the output of the first buffer and a second input configured to be coupled to the output of the register, the multiplexer further having a selection terminal and an output;

a second buffer having an input configured to be coupled to the output of the multiplexer, an output configured to be coupled to the bidirectional data bus, and an activation terminal; and

bypass control logic configured to generate a control signal applied to the selection terminal to control the multiplexer and applied to the activation terminal to control the second buffer.

3. The logic circuit of claim 2, further comprising:

control logic configured to enable or disable the second buffer responsive, at least in part, to receipt of an activation signal.

4. The logic device of claim 1, further comprising a memory device interface configured to couple to at least one memory device.

5. The logic device of claim 1, further comprising control logic coupled to the bypass circuit and configured to generate a control signal to control the bypass circuit to store the write data and restore the write data.

6. The logic device of claim 1 wherein the bypass circuit is configured to store the write data and restore the write data responsive at least in part to a control signal provided by a memory controller.

7. The logic device of claim 1 wherein the logic circuit is included in a memory hub.

8. The logic device of claim 1 wherein the bypass circuit is configured to decouple and temporarily store write data from the bidirectional data bus in a data storage device during the execution of a read operation and restore the decoupled write data to the bidirectional data bus once the read operation has ended.

9. A memory logic circuit comprising:

first and second data bus interfaces coupled to a bidirectional data bus configured to transfer read data in a first direction between the first and second data bus interfaces and configured transfer write data in a second direction opposite of the first direction between the first and second data bus interfaces;

a bypass circuit coupled to the first and second data bus interfaces and configured to store write data from the data bus while read data is transferred over the data bus between the first and second data bus interfaces in the first direction and restore write data to the data bus in the second direction when the read data has finished transmitting; and

control logic configured to control the bypass circuit responsive to a bypass signal.

10. The memory logic circuit of claim 9, further comprising a first memory interface configured to couple memory commands to at least one memory.

11. The memory logic circuit of claim 9 wherein the first or second data bus interface is configured to be coupled to a memory controller via the bidirectional bus.

12. The memory logic circuit of claim 9 wherein the bypass circuit is configured to store write data in a FIFO register.

13. The memory logic circuit of claim 9 wherein the bypass circuit comprises a non-bypass write data path and a bypass write data path having a bypass register configured to store the write data.

14. The memory logic circuit of claim 9 wherein the write data is transferred back to the bidirectional data bus a specified amount of time after it is stored.

15. The memory logic circuit of claim 9 wherein the memory logic circuit is included in a memory hub.

16. A write data bypass circuit to store and transmit write data on a bidirectional memory bus, comprising:

a first buffer coupled to the bidirectional bus configured to receive data from and transmit data in a first direction on the bidirectional data bus;

a data storage device configured to receive and store write data transmitted in a second direction opposite of the first direction from the bidirectional data bus during the execution of a read operation to prevent a data collision;

a multiplexer configured to select between the output of the first buffer or the data storage device;

a second buffer coupled to the multiplexer and configured to be enabled or disabled to control output from the write data bypass circuit; and

bypass control logic configured to control the multiplexer and the second buffer in order to restore write data to the bidirectional data bus to be transmitted in the second direction thereon,

wherein the bypass control logic is configured to be controlled responsive to a bypass signal.

17. The write data bypass circuit of claim 16 wherein the data storage device comprises a FIFO register.