SDRAM sharing using a control surrogate
View Patent ↗A system and method for sharing a single synchronous dynamic random access memory (SDRAM) unit between two chips, each having an SDRAM controller. Each SDRAM controller is effectively divided into a control block and a data block. The first SDRAM controller drives or reads directly from the SDRAM unit's data bus instead of employing a dedicated data bus for communication between the first and second SDRAM units. The data section of the second SDRAM controller responds to requests from the first SDRAM controller as if the requests had come from the second SDRAM controller's own control block. In other embodiments of the present invention, the second SDRAM controller can accept control signals generated by the first SDRAM. If the second SDRAM controller detects that the first SDRAM controller is initiating a request, the second SDRAM controller terminates any active requests of its own using burst termination. Thereafter, the second SDRAM controller processes the first SDRAM controller's request with the SDRAM unit as appropriate.
1. A method of sharing synchronous dynamic random access memory, comprising:
partitioning a first synchronous dynamic random access memory controller into a control block and a data block;
configuring the first synchronous dynamic random access memory controller to receive at least one data request from the control block of the first synchronous dynamic random access memory controller and at least one data request from a second synchronous dynamic random access memory controller;
driving a clock signal used by both of the first and second synchronous dynamic random access memory controllers from the control block of the first synchronous dynamic random access memory controller; and
controlling the synchronous dynamic random access memory using control signals from the control block of the first synchronous dynamic random access memory controller.
2. The method of claim 1 , wherein the at least one data request received from the second synchronous dynamic random access memory controller is received over a system bus communicatively connecting the first and second synchronous dynamic random access memory controllers.
3. The method of claim 1 , wherein the second synchronous dynamic random access memory controller shares a data bus with the synchronous dynamic random access memory.
4. The method of claim 1 , wherein the controlling of the synchronous dynamic random access memory further comprises using sideband signaling by the second synchronous dynamic random access memory controller to inform the first synchronous dynamic random access memory controller of the at least one data request from the second synchronous dynamic random access memory controller.
5. The method of claim 4 , wherein the sideband signaling is communicated to the first synchronous dynamic random access memory using a sideband port of the first synchronous dynamic random access memory and wherein the sideband port is configured to receive bank address, activate/close, read/write, clock, clock enable, column address select, row address select, write enable, and chip select signals.
6. The method of claim 1 , wherein upon receipt of a data request from the second synchronous dynamic random access memory controller, any active data requests by the first synchronous dynamic random access memory controller are terminated.
7. The method of claim 6 , wherein the terminating of any active data requests further comprises:
doubling a number of clock signal cycles the first synchronous dynamic random access memory controller has to terminate its own active data requests; and
configuring the second synchronous dynamic random access memory controller to buffer data as it arrives from the synchronous dynamic random access memory.
8. The method of claim 6 , wherein the terminating of any active data requests further comprises:
decreasing a clock signal frequency of the synchronous dynamic random access memory; and
providing the clock signal from the first synchronous dynamic random access memory controller to the second synchronous dynamic random access memory controller.
9. The method of claim 6 , wherein the terminating of any active data requests further comprises configuring the second synchronous dynamic random access memory controller to treat the synchronous dynamic random access memory as double-data-rate synchronous dynamic random access memory.
10. A synchronous dynamic random access memory controller comprising:
a control block configured to transmit at least one of a plurality of control signals to a synchronous dynamic random access memory;
a data block configured to transmit and receive data to and from the synchronous dynamic random access memory, and receive a clock signal from one of the control block and an off-chip synchronous dynamic random access memory controller; and
a system interface configured to receive on-chip data requests and to receive off-chip data requests from the off-chip synchronous dynamic random access memory controller; and
wherein the control block is configured to control the synchronous dynamic random access memory for both the on-chip data requests and the off-chip data requests.
11. The synchronous dynamic random access memory controller of claim 10 , wherein the synchronous dynamic random access memory controller is configured to share a data bus with a synchronous dynamic random access memory and the off-chip synchronous dynamic random access memory controller.
12. The synchronous dynamic random access memory controller of claim 11 , wherein the synchronous dynamic random access memory controller is configured to control the synchronous dynamic random access memory.
13. The synchronous dynamic random access memory controller of claim 10 , further configured to receive at least one of a plurality of control signals from off-chip synchronous dynamic random access memory controller.
14. The synchronous dynamic random access memory controller of claim 10 , wherein upon receipt of a data request from the off-chip synchronous dynamic random access memory controller, any active data requests by the synchronous dynamic random access memory controller are terminated.
15. The synchronous dynamic random access memory controller of claim 14 , wherein the terminating of any active data requests further comprises:
doubling a number of clock signal cycles the synchronous dynamic random access memory controller has to terminate its own active data requests; and
configuring the off-chip synchronous dynamic random access memory controller to buffer data as it arrives from a synchronous dynamic random access memory communicatively connected to the synchronous dynamic random access memory controller.
16. The synchronous dynamic random access memory controller of claim 14 , wherein the terminating of any active data requests further comprises:
decreasing a clock signal frequency of a synchronous dynamic random access memory communicatively connected to the synchronous dynamic random access memory controller; and
providing a clock signal from the synchronous dynamic random access memory controller to the off-chip synchronous dynamic random access memory controller.
17. The synchronous dynamic random access memory controller of claim 14 wherein the terminating of any active data requests further comprises, configuring the off-chip synchronous dynamic random access memory controller to treat the synchronous dynamic random access memory communicatively connected to the synchronous dynamic random access memory controller as double-data-rate synchronous dynamic random access memory.
18. A system for sharing synchronous dynamic random access memory, comprising:
a first synchronous dynamic random access memory controller partitioned into a control block and a data block;
a second synchronous dynamic random access memory controller communicatively connected to the first synchronous dynamic random access memory controller, wherein the first synchronous dynamic random access memory controller is configured to receive at least one data request from the control block of the first synchronous dynamic random access memory controller and at least one data request from the second synchronous dynamic random access memory controller; and
a synchronous dynamic random access memory communicatively connected to the first and the second synchronous dynamic random access memory controllers, wherein
a data bus is shared by the first and the second synchronous dynamic random access memory controllers and the synchronous dynamic random access memory;
a clock signal used by the first and the second synchronous dynamic random access memory controllers is driven by the control block of the first synchronous dynamic random access memory controller; and
the control block of the first synchronous dynamic random access memory controller is used to control the synchronous dynamic random access memory for both the at least one data request from the control block of the first synchronous dynamic random access memory controller and the at least one data request from the second synchronous dynamic random access memory controller.
19. The system of claim 18 , wherein the first synchronous dynamic random access memory controller is configured to terminate any active data requests of the first synchronous dynamic random access memory controller in response to receiving a data request from the second synchronous dynamic random access memory controller.
20. The method of claim 1 , wherein the controlling of the synchronous dynamic random access memory using control signals from the control block of the first synchronous dynamic random access memory controller comprises controlling the synchronous dynamic random access memory using the control signals from the control block of the first synchronous dynamic random access memory controller for both the at least one data request from the control block of the first synchronous dynamic random access memory controller and the at least one data request from the second synchronous dynamic random access memory controller.