System and Method for Interleaving Memory Banks

The present invention is directed to a device and method which automatically determine whether to interleave pairs of memory banks. More particularly, the present invention maps address bus bits to memory addresses in interleaved and non-interleaved modes which support desired row and column configurations of the memory as stored in a register file.

It is known to interleave memory banks to provide double wide memories so that the memory is used more efficiently. To interleave memory banks in known memory systems, certain types of single in line memory modules (SIMMs) must be placed in the corresponding sockets of a memory motherboard and DIP switches must be set to be indicative of the SIMMs placed in the sockets. Accordingly, these interleaved memory banks require a great deal of user interaction and knowledge. Also, either every memory bank pair in the known memory system must be interleaved or all of the memory banks must operate in a non-interleaved fashion in the known systems. In other words, previous systems do not allow a portion of the memory banks to be interleaved while the remaining portions operate in a non-interleaved fashion. In order to properly operate, each of the SIMMs used must additionally have the same type of row/column configuration, size and speed for interleaving.

One example of a system using interleaved memory is the Macintosh Quadra 800 (Apple Computer, Cupertino, Calif.). In this system, addressing and interleaving signals are all multiplexed together in a single stage. Because the Quadra 800 system has a relatively small number of memory banks (the Quadra 800 has 5 memory bank pairs), a significant delay in producing the end product to the memory does not result. However, as the number of bases in this system increases, the row addresses from the input bus and the interleaving signals are subjected to significantly more logic functions. Therefore, a large delay of the addressing and interleaving signals propagates through to the end product for the memory, and the generation of the interleaving and addressing signals takes more time and slows down the system.

It is therefore desired to provide a system and method for reducing the delays i producing the end product to the memory having a large number of memory banks where portions of the memory banks are interleaved. The present invention is also directed to reducing the amount of user interface necessary to configure a memory system and to increase the efficiency of the memory system by automatically interleaving the memory bank pairs which have the same row and column configurations.

An object of the present invention is to provide a device and method for automatically interleaving the memory bank pairs which have the same row and column configurations so that the memory performance is improved by reducing the delays in producing the end product to the memory having a large number of memory bank pairs.

Another object of the present invention is to map address bus bits to memory address bits with two different modes which support desired row and column configurations as stored in a register file.

These objects of the present invention are fulfilled by providing a device for determining whether to interleave pairs of memory banks comprising a register file for storing bank bases and their associated address modes for a plurality of memory configurations, and an interleaving analyzing unit for comparing the configurations of the pairs of the memory banks to the bank bases stored in said register file corresponding to an input address and interleaving the pairs when the configurations are the same for each memory bank in the pairs. This device automatically interleaves each pair of the memory banks which have the same row and column configuration while the pairs of memory banks which do not have the same row and column configuration are not interleaved. As a result, the memory performance is improved by being operated in the most efficient manner with a minimal amount of user intervention.

These objects of the present invention are also fulfilled by providing a method for determining whether to interleave pairs of memory banks comprising the steps of storing bank bases and their associated address modes for a plurality of configurations in a register file, comparing the configurations of the pairs of the memory banks to said bank bases stored in said register file corresponding to an input address, and interleaving the pairs when the configurations are the same for each memory bank in the pairs. This method automatically interleaves the pairs of the memory banks which have the same row and column configurations so the memory performance is enhanced.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent from those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

FIG. 1 illustrates a block diagram of the memory control device according to an embodiment of the present invention;

FIG. 2 illustrates a more detailed view of the banked code used in an embodiment of the present invention;

FIG. 3 illustrates a more detailed view of the mapping unit used in an embodiment of the present invention;

FIG. 4 illustrates an example of a memory module configuration for an embodiment of the present invention; and

FIG. 5 illustrates a flow chart for an embodiment of the present invention.

FIG. 1 shows a block diagram for a memory controller according to an embodiment of the present invention. In FIG. 1, a register file 10 for storing bases of the memory banks and their associated address modes, a bank decoder 20 for developing interleave enable, address mode and odd bank signals in response to an address bus input thereto, a mapping unit 30 for mapping the address bus bits based on the bank decoder 20 to a memory 40. This memory controller maps the bits from the address bus to addresses for the memory 40 in two different modes to support every desired memory configuration stored in the register file 10.

One example of the memory sizes that may be supported by the present memory controller using 4M technology DRAMs is illustrated below in Table 1.

Table 1 is an illustrative example of the maximum memory sizes that may be supported for specific examples of the present invention and is not intended to be limitative for all of the maximum memory sizes that may be supported by this memory control.

FIG. 2 provides a more detailed illustration of the bank decoder 20 used in an embodiment of the present invention. The bank decoder 20 includes a plurality of less than comparators 22.sub.0, 22.sub.1, . . . 22.sub.n which are input to a signal processor 24 for generating the interleave enable, address mode and odd bank signals. The less than comparators 22.sub.0, 22.sub.1, . . . 22.sub.n compare bits from the address bus to bits from the register file 10. For example, the register file 10 includes bank bases and associated address modes which are 8 bits wide with 2 entries per bank where the LSB correspond to the base addresses and 3 of the MSB correspond to interleave enable, address mode and odd bank states. Then, the signal processor receives the output from each of these comparators 22.sub.0, 22.sub.1, . . . 22.sub.n and performs a logical operation to generate the interleave enable, address mode and odd bank signals. The logical operation performed by the signal processor 24 is an AND/OR comparison of the bits from the register file 10 corresponding to the interleave enable, address mode or odd bank. More specifically, the logical operation for interleave enable is:

where ADRLT represents a less than comparison of the address and INTEN represents the interleave enable bit of the register file 10. The logical operation for the address mode is performed similar to the interleave enable. The address mode signal is calculated according to the following relations:

where ADRMODE represents the address mode bit from the register file 10. The odd bank signal is generated according to the following operation:

In FIG. 3, a more detailed illustration of the mapping unit 30 is provided. The mapping unit 30 includes four multiplexers for multiplexing the row and column addresses from the address bus. The output from the multiplexers 32.sub.1, 32.sub.2, 32.sub.3, and 32.sub.4 are respectively inputted to four registers 34.sub.1, 34.sub.2, 34.sub.3, and 34.sub.4. For instance, if the outputs of the multiplexers 32.sub.1, 32.sub.2, 32.sub.3 and 32.sub.4 are 12 bits wide, 12 bit registers are used and output four 12 bit signals. The four registers correspond to non-interleaved and interleaved modes for adjacent banks and are used in the remapping process. In particular, the two registers 34.sub.1 and 34.sub.2 correspond to the non-interleaved mode and the two registers 34.sub.3 and 34.sub.4 correspond to the interleaved mode. The outputs from the registers 34.sub.1, 34.sub.2, 34.sub.3, and 34.sub.4 are remapped by the multiplexer 36 in response to the interleave enable and address mode signals generated by the bank decoder 20. The output of the multiplexer 36 is then input to an amplifier 38 in order to generate the memory address.

In an illustrative example for the present invention, the memory controller may support a 128 bit wide, 2 bank interleaved operation or a 64 bit wide, single bank operation selectable on a per bank basis. FIG. 4 illustrates an example of a memory configuration 40 for an embodiment of the present invention. In this example, motherboard banks 0 and 1 are soldered on the motherboard as a single interleaved set which yields 8M Bytes with 16 512K.times.8 DRAMs. Alternatively, 32 1M.times.4 parts could be soldered to the motherboard as a single interleaved set to yield 16M Bytes of on-board memory. In addition to the on-board memory, sockets corresponding to SIMM 0 through SIMM 11 are provided. When both memory banks in a pair are present, the pair of memory banks are cycled at the same time, with data from one memory bank transferred onto the address bus before the data from the other memory bank. For a 32 byte burst transaction, the DRAMs are cycled two times and when a single memory bank in a pair is present, the bank is cycled four times. To properly configure the memory system in this example, each bank of SIMMs is assigned a base address with a pair of registers that are concatenated together to form an 11 bit register for defining the base address, the addressing mode and whether the bank is interleaved with its companion bank. For the example illustrated in FIG. 4, 26 pairs of these registers are implemented to control two banks of on-board memory and 24 banks of expansion SIMMs (12 double-sided SIMM sockets).

When the interleave enable bit is set, a given set of memory banks will operate an interleaved set of memory banks for providing double-wide memory. This interleave enable bit is only implemented for the even banks and the bit for the odd bank is always set. The address mode bit in the register file 10 configures the mapping of the address bus bits to memory RAS/CAS address bits for enabling support of all configurations of 1, 4, 16, and 64M DRAMs corresponding to one set of memory configurations. Table 2 below summarizes address mode bit settings for 1M, 4M, 16M and 64 DRAMs.

The base address field in the register file 10 is used as the base address that the address bus addresses are compared to. If these address bits are greater than or equal to this field and less than the value of bank n+1 base, the given base is selected.

The address bus to memory address mapping for non-interleaved banks is illustrated below in Table 3 for non-interleaved banks.

The mapping of the address bus to memory address for interleaved banks is illustrated below in Table 4.

To properly configure the memory controller, the following memory sizing operation is performed upon starting up as illustrated by the flow chart in FIG. 5. To determine whether the size of adjacent memory banks may be interleaved, the size of the adjacent memory banks are analyzed to determine whether they are the same. At step S10 of FIG. 5, each bank base is set to be 16'B0000 000n nnnn 0000, for example, where n is the binary bank number. Also at step S10, the bank is sized by clearing the address mode bit. Next, it is determined at step S20 whether the bank size is the power of 2. If the bank size is determined not to be a power of 2 at step S20 (the size of 5 MB or 13 MB, for instance), step S30 is executed. At step S30, each bank base is set to be 16'B0000 001n nnnn 0000 in this example. The bank is also sized at step S30 with the address mode bit being set. If the bank size is determined to be a power of 2 at step S20, or after completing step S30, step S40 is executed where the base address field is programmed for each bank with the first nine bits of the first address in the bank. The first address of a given bank is a function of the sum of the sizes of all lower numbered banks. Then, it is determined at step S50 whether a given set of adjacent banks are the same size and have identical addressing modes. If it is determined at step S50 that the adjacent banks are the same size and their address modes are identical, the interleave bit is set in the even memory bank base register for performing an interleave operation at step S60. If the given set of adjacent banks are not the same size or their addressing modes are not identical, the interleave bit is set to 0 and the non-interleave operation is performed.

The embodiments of the present invention allow address bus bits to be mapped to memory address bits in two different modes for supporting each desired memory configuration. Furthermore, the performance of the memory is improved by automatically determining the pairs of memory banks having the same size the row/column configuration. As a result, the memory operates with a combination of interleaved and non-interleaved memory bank pairs. Also, the present invention eliminates the user interaction necessary to determine whether interleaving is possible and the corresponding set-up operations for interleaving.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.