Multi-rank memory module that emulates a memory module having a different number of ranks
View Patent ↗A transparent four rank memory module has a front side and a back side. The front side has a third memory rank stacked on a first memory rank. The back side has a fourth memory rank stacked on a second memory rank. An emulator coupled to the memory module activates and controls one individual memory rank from either the first memory rank, the second memory rank, the third memory rank, or the fourth memory rank based on the signals received from a memory controller.
1. A memory module connectable to a computer system, the memory module comprising:
a board;
a first plurality of double-data-rate (DDR) memory devices mounted to the board, the first plurality of DDR memory devices arranged in a first number of ranks; and
a circuit that is coupled to said board and that receives from the computer system a set of input control signals that includes a set of first chip select signals and an address signal, and that generates a set of second chip select signals based at least in part upon values of said set of first chip select signals and a portion of the address signal;
wherein the size of the received set of first chip select signals is smaller than the size of the generated set of second chip select signals;
wherein the received set of first chip select signals includes at least two chip select signals and the generated set of second chip select signals includes at least four chip select signals;
wherein the chip select signals of the generated set of second chip select signals correspond to the first number of ranks;
wherein the chip select signals of the received set of first chip select signals correspond to a second plurality of DDR memory devices arranged in a second number of ranks;
wherein the second number of ranks is less than the first number of ranks;
wherein at least one signal of the generated set of second chip select signals has a value to select DDR memory devices of a respective rank of the first number of ranks;
wherein the circuit provides one or more of the set of input control signals to said respective selected rank;
wherein the set of input control signals includes RAS, CAS, WE, and BA;
wherein the circuit includes an emulator and a register;
wherein the emulator receives from the computer system at least a portion of the set of input control signals that includes: RAS, CAS, WE, the received set of first chip select signals, and the portion of the address signal;
wherein the emulator generates the generated set of second chip select signals in response to at least RAS, CAS, WE, and the received set of first chip select signals;
wherein the emulator generates the generated set of second chip select signals with only one signal of the generated set of second chip signals having a value to select DDR memory devices of a respective rank of the first number of ranks, in response to a portion of the input control signals, including the portion of the address signal, received by the emulator;
wherein the emulator generates the generated set of second chip select signals with at least two signals of the generated set of second chip signals having values to select DDR memory devices of at least two respective ranks of the first number of ranks, in response to a portion of the input control signals indicating a refresh, received by the emulator;
wherein the register receives at least another portion of the set of input control signals that includes RAS, CAS, WE, BA, and the remaining portion of the address signal; and
wherein the register provides one or more of the input control signals received by the register to DDR memory devices of said at least one respective selected rank.
2. The memory module of claim 1 , wherein the number of DDR memory devices per rank in the first number of ranks is the same as the number of DDR memory devices per rank in the second number of ranks.
3. The memory module of claim 1 , wherein the number of DDR memory devices per rank in the first number of ranks and the number of DDR memory devices per rank in the second number of ranks is 9.
4. The memory module of claim 1 , wherein the first number of ranks is twice the second number of ranks.
5. The memory module of claim 1 , wherein the first number of ranks is four and the second number of ranks is two.
6. The memory module of claim 1 , wherein the received set of first chip select signals consists of two signals and the generated set of second chip select signals consists of four signals.
7. The memory module of claim 1 , wherein the portion of the address signal includes only a single bit.
8. The memory module of claim 1 , wherein the first plurality of DDR memory devices and the second plurality of DDR memory devices have the same memory density.
9. The memory module of claim 1 , wherein the received set of first chip select signals includes a first received chip select signal and a second received chip select signal, wherein the received first and second chip select signals are configured to always have opposite digital values during generation of the set of second chip select signals for use in a read access or a write access operation.
10. The memory module of claim 1 , wherein the number of DDR memory devices in the first plurality of DDR memory devices mounted to the board is more than the number of DDR memory devices in the second plurality of DDR memory devices.
11. A memory module connectable to a computer system, the memory module comprising:
a board;
a first plurality of double-data-rate (DDR) memory devices mounted to the board, the first plurality of DDR memory devices arranged in a first number of ranks; and
a circuit that is coupled to said board and that receives from the computer system a set of input control signals that includes a set of first chip select signals and an address signal, and that generates a set of second chip select signals based at least in part upon values of said set of first chip select signals and a portion of the address signal;
wherein the size of the received set of first chip select signals is smaller than the size of the generated set of second chip select signals;
wherein the received set of first chip select signals includes at least two chip select signals and the generated set of second chip select signals includes at least four chip select signals;
wherein the chip select signals of the generated set of second chip select signals correspond to the first number of ranks;
wherein the chip select signals of the received set of first chip select signals correspond to a second plurality of DDR memory devices arranged in a second number of ranks;
wherein the second number of ranks is less than the first number of ranks;
wherein the set of input control signals includes RAS, CAS, WE, and BA;
wherein the circuit includes an emulator that receives from the computer system at least a portion of the set of input control signals that includes: RAS, CAS, WE, the received set of first chip select signals, and the portion of the address signal;
wherein the emulator generates the generated set of second chip select signals in response to at least RAS, CAS, WE, and the received set of first chip select signals;
wherein the emulator generates the generated set of second chip select signals with only one signal of the generated set of second chip signals having a value to select DDR memory devices of a respective rank of the first number of ranks, in response to a portion of the input control signals, including the portion of the address signal, received by the emulator;
wherein the emulator generates the generated set of second chip select signals with at least two signals of the generated set of second chip signals having values to select DDR memory devices of at least two respective ranks of the first number of ranks, in response to a portion of the input control signals indicating a refresh, received by the emulator;
wherein the emulator provides individual chip select signals from the generated set of second chip select signals to DDR memory devices of individual ranks of the first number of ranks; and
wherein the circuit provides one or more of RAS, CAS, WE, BA, and a remaining portion of the address signal to DDR memory devices of at least the respective selected rank of the first number of ranks.
12. The memory module of claim 11 , wherein the emulator allows the computer system, which provides the number of chip select signals in the received set of first chip select signals, to interface with the first number of ranks, wherein the number of chip select signals in the received set of first chip select signals corresponds to the second number of ranks, and wherein the number of chip select signals in the generated set of second chip select signals corresponds to the first number of ranks.
13. The memory module of claim 11 , wherein the circuit provides the one or more of RAS, CAS, WE, BA, and the remaining portion of the address signal to individual ones of the first number of ranks.
14. The memory module of claim 11 ,
wherein the circuit includes a register;
wherein the register receives at least another portion of the set of input control signals that includes: RAS, CAS, WE, BA, and the remaining portion of the address signal; and
wherein the register provides the one or more of RAS, CAS, WE, BA, and the remaining portion of the address signal to at least the respective selected rank of the first number of ranks.
15. The memory module of claim 11 ,
wherein the number of chip select signals of the generated set of second chip select signals corresponds to a first number of DDR memory devices arranged in the first number of ranks; and
wherein the number of chip select signals of the received set of first chip select signals corresponds to a second number of DDR memory devices arranged in the second number of ranks.
16. The memory module of claim 11 , wherein the received set of first chip select signals includes a first received chip select signal and a second received chip select signal, wherein the received first and second chip select signals are configured to always have opposite digital values during generation of the set of second chip select signals for use in a read access or a write access operation.
17. A memory module connectable to a computer system, the memory module comprising:
a board;
a first plurality of double-data-rate (DDR) memory devices mounted to the board, the first plurality of DDR memory devices arranged in a first number of ranks; and
a circuit that is coupled to said board and that receives from the computer system a set of input control signals that includes a set of first chip select signals and an address signal, and that generates a set of second chip select signals based at least in part upon values of said set of first chip select signals and a portion of the address signal;
wherein the size of the received set of first chip select signals is smaller than the size of the generated set of second chip select signals;
wherein the second number of ranks is less than the first number of ranks;
wherein the received set of first chip select signals includes a first received chip select signal and a second received chip select signal, wherein the received first and second chip select signals are configured to always have opposite digital values during generation of the set of second chip select signals for use in a read access or a write access operation;
wherein the chip select signals of the generated set of second chip select signals correspond to the first number of ranks;
wherein the chip select signals of the received set of first chip select signals correspond to a second plurality of DDR memory devices arranged in a second number of ranks;
wherein the set of input control signals includes RAS, CAS, WE, and BA;
wherein the circuit includes an emulator;
wherein the emulator allows the computer system, which provides the number of chip select signals in the received set of first chip select signals, to interface with the first number of ranks, wherein the number of chip select signals in the received set of first chip select signals corresponds to the second number of ranks, and wherein the number of chip select signals in the generated set of second chip select signals corresponds to the first number of ranks;
wherein the emulator receives from the computer system at least a portion of the set of input control signals that includes: RAS, CAS, WE, the received set of first chip select signals, and the portion of the address signal;
wherein the emulator generates the generated set of second chip select signals in response to at least RAS, CAS, WE, and the received set of first chip select signals;
wherein the emulator generates the generated set of second chip select signals with only one signal of the generated set of second chip signals having a value to select DDR memory devices of a respective rank of the first number of ranks, in response to a portion of the input control signals, including the portion of the address signal, received by the emulator;
wherein the emulator generates the generated set of second chip select signals with at least two signals of the generated set of second chip signals having values to select DDR memory devices of at least two respective ranks of the first number of ranks, in response to a portion of the input control signals indicating a refresh, received by the emulator;
and
wherein the emulator provides individual chip select signals from the generated set of second chip select signals to DDR memory devices of individual ranks of the first number of ranks.
18. The memory module of claim 17 , wherein a number of DDR memory devices in the first plurality of DDR memory devices mounted to the board is more than a number of DDR memory devices in the second plurality of DDR memory devices.
19. The memory module of claim 17 ,
wherein the circuit includes a register that receives at least another portion of the set of input control signals that includes RAS, CAS, WE, BA, and the remaining portion of the address signal; and
wherein the register provides the one or more of RAS, CAS, WE, BA, and the remaining portion of the address signal to DDR memory devices of at least the respective selected rank of the first number of ranks.