Cache memory control apparatus for a virtual memory data-processing system

Abstract: Disclosed is a buffer memory control apparatus, in which a translation lookaside buffer (51, 61, 71) for translating a logical address into a real address to make an access to a buffer storage (81) has a logical address storage portion (51) and a real address storage portion (61, 71) to each of which logical address bits are entered at its column. Column identifying address bits for the logical address storage portion partly overlap on column identifying address for a buffer address array for holding a real address to be supplied to the buffer storage, so that the buffer address array, the real address storage portion, and a comparator circuit for comparing the contents held by the buffer address array and the real address storage portion are divided into sections corre­ sponding to the overlapped a part of bits and the sections are suitably combined and arranged as circuits.

Description: BACKGROUND OF THE INVENTION The present invention relates to a buffer memory control apparatus. Such a circuit for controlling a buffer memory is disclosed in U.S. Patent No. 4,332,010 and JP-B-57-57784. The latest large-sized and medium-sized electronic computers generally employ a virtual storage system as well as a buffer memory system. The virtual storage system is a system in which a programmer is made possible to execute coding without being conscious of the size of a real storage and the programmer is given not a real address on a real storage but a logical address on a virtual storage. On the other hand, the buffer storage system in a system in which a high-speed and small capacity buffer storage is disposed in a main storage so as to stop a gap in the main storage to thereby form a storage hierarchical structure because the main storage is low in processing speed in comparison with an operation speed of the computer while the main storage is large in capacity. In such a virtual storage system, it is necessary to translate a logical address into a real address prior to making reference to the main storage. The translation of a logical address into a real address is carried out by making reference to an address translation table prepared in a program. If such reference is made to the low speed main storage every time translation is to be made, the overhead taken for the translation is large. In this regard, there is provided a translation lookaside buffer (hereinafter abbreviated to "TLB") for storing pairs of logic-address to real address translation which have been obtained by making reference to the main storage, so that when reference is to be made to the main storage, a judgement is made whether the logical address in question exists in the TLB or not prior to making the reference, and if the logical address exists in the TLB (the probability of this existence is very high because of locality of a program), the real address corresponding to the logical address can be obtained at a high speed from the TLB. In the buffer storage system, on the other hand, the buffer storage is a copy of a part of the main storage and therefore a buffer address array (hereinafter abbreviated to "BAA") is provided in the buffer storage. If a central processing unit starts the main storage reference with a logical address, a judgement is made as to whether a real address corresponding to the logical address translated by the TLB exists in the BAA or not so that when the real address exists in the BAA (the probability of this existence is very high because of locality of a program), necessary data is read out from the buffer storage at a high speed and sent to the central processing unit. Although the above description has been made such that the reference to the TLB and BAA is made serially, it is necessary to make the reference parallelly in order to make the processing speed high. In this case, the BAA is referred to with a logical address. A BAA column can be identified using a real address portion within a logical address or at an intra-page address as described in US-A-4 332 010 and in EP-A-264 912, the latter being an intermediate document according to Art. 54(3) EPC. Alternatively it can be identified by a logical address or an address including a part of a page address to be subject to address translation. In the latter case, there is an overlapping in bits of the respective identification addresses to be given to the TLB and BAA. Such a system having the characteristics of the preamble of claim 1 is described in EP-A-224 168. Fig. 1 is a block diagram showing a part of a buffer storage device of the system in which reference is made to the above-mentioned TLB and BAA parallelly. Upon generation of a memory request from a central processing unit, a logical address is stored in a register 91. The entry of the logical address in a TLB 92 is identified by a lower bit b of an upper-rank page address of the logical address. In this example, the TLB 92 is composed of k columns x 2 rows, and the reference numerals 92-1 and 92-2 represent first and second rosw respectively. That is, each of the first and second rosw has k entries. Each entry in each of the first and second rosw 92-1 and 92-2 of the TLB 92 is composed of a logical address portion (L), a validity flag bit portion (V), and a real address portion (R). The logical address portion and real address portion of the TLB are called TLBLA and TLBRA respectively. The contents of the portions L and V read out from each row of the TLB 92 are compared with an upper bit a of the page address in the register 91 by corresponding logical address comparators 94-1 and 94-2 respectively. The BAA is identified with an upper bit c of a lower rank intra-page address of a virtual address. In this embodiment, the BAA 93 is composed of ℓ columns x 2 rows and the reference numerals 93-1 and 93-2 represent first and second rows respectively. That is, each row has ℓ entries. Each entry of the BAA 93 is composed of a real address portion (R) and a validity flag bit portion (V). Real address comparators 96-1 and 96-2 compare a real address (intra-page address or displacement) read out from the portion R of the TLB 92-1 and entered through a selector 95 or a real address (intra-page address or displacement) directly stored in the register 91 by the central processing unit with the contents read out from the portion R of the corresponding row 93-1 or 93-2 of the BAA 93. The selector 95 is arranged to select the contents of the register 91 when the central processing unit has stored a real address directly in the register 91 while select the contents of the row 92-1 of the TLB 92 when a logical address has been stored in the register 91. Other comparators 97-1 and 97-2 are arranged to compare the real address read out from the portion R of the row 92-2 of the TLB 92 with the real address read out from the portion R of the corresponding rows 93-1 and 93-2 of the BAA 93. Upon detection of coincidence between the two inputs, the output of each of the real address comparators 96-1, 96-2, 97-1 and 97-2 becomes "1". The results of comparison by the real address comparators 96-1, 96-2, 97-1 and 97-2 are entered into an encoder 98, and after selected, an encoded output (one bit in this example) of the encoder 98 is stored in a upper bit of a register 99. An intra-page address of the register 91 is stored in a lower bit of the register 99. Thus, a buffer storage address corresponding to the logical address or real address stored in the register 91 is obtained. A buffer storage is identified with this address of the register 99 and the data thus read out from the buffer storage is transferred to the central processing unit. Requiring a high speed property as well as a certain capacity, the TLB 92 and BAA 93 are generally constituted by bipolar memories. Fig. 2 shows a bipolar memory to be used for such a purpose. In Fig. 2, after decoded in an X-address decoder 110 and a Y-address decoder 114, address signals applied to input pins A₀ - A₂ and A₃ - A₅ of the X- and Y-address decoders 110 and 114 actuate a memory cell 112 through drivers 111 and 113 respectively. In this example, the memory cell 112 is composed of 8 x 8 bits, that is, 64 bits. A selected one bit of the memory cell 112 is led to an output circuit 116 through a sense amplifier 115. The mode becomes a write mode when an input WE (write enable) is valid. In the write mode, an input DI (data-in) is passed through a gate 117 so as to be ANDed with the WE in an AND 118 and another AND 119. Write "1" or Write "0" is made valid by the outputs of the ANDs 118 and 119 so as to give write instructions, through the driver 113, to the bit of the memory cell 112 designated through the address inputs A₀ - A₅. When used as the aforementioned TLB or BAA, the bipolar memories of the kind as described above are arranged in the form of a matrix to thereby realize a desired word length as well as a desired bit length. The recent development and improvement of extra high density LSIs has begun to make it possible to realize making electronic computers large in scale and high in processing speed. This tendency is considered to be promoted also from now on. Further, there is a tendency that a main storage becomes large in its capacity and therefore it is required to make the capacity of a buffer storage large. That is, it is required to increase the BAA capacity. On the other hand, the technique to make bipolar memories highly integrated has been promoted so that it has become possible to realize high speed memories. However, it is not easy to realize a structure of a large capacity BAA by using bipolar memories having such a structure as described above with respect to Fig. 2, because it is required to extremely increase the number of package pins of the bipolar memories. For example, in the case where a 4K-bit memory is composed of 64 words, each word can accommodate 64 bits, however, about 140 pins are required for address lines, data lines, control lines, and power supply lines, so that the package size of the bipolar memory is limited by the number of those input and output pins. The above JP-B-57-57784 discloses a device in which a TLB and a BAA are constituted by memories of the type in which comparators are included in an LSI for the BAA. For example, in the JP-B-57-57784, it is intended to solve the above problems by making the portions encircled by broken lines in Fig. 1 be incorporated in a memory chip. In the above JP-B-57-57784, a real address read out from the TLB is once led to the outside and then entered into the memory chip constituting the BAA so that the real address is compared with a real address read out from the BAA. There is therefore a problem that the number of pins required for input and output of the TLB and BAA increases and propagation delay also increases. There is a further problem that the communication path among the TLB, BAA, comparators provided in a single LSI becomes so long that the signaling time among those elements is prolonged. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a buffer memory control apparatus in which the above problems of the prior art are eliminated and the propagation delay as well as the number of the input and output pins of the package are reduced. It is another object of the present invention is to provide a buffer memory control apparatus in which it is made possible to read out and write data corresponding to a given logical address from and into a buffer memory at a high speed. In order to achieve the above objects, according to the present invention, each of TLBRA and BAA is divided into a plurality of sections with respect to identification logical addresses in each column in such a manner that logical addresses which are quite within the bounds of possibility of simultaneous identification are stored in a region in which transfer of information can be executed at a high speed, for example, one and the same LSI. According to the present invention, since each pair of corresponding units of TLBRA and BAA each divided into a plurality of units are incorporated in adjacent regions within one LSI, it is possible to reduce the propagation delay as well as to reduce the number of the input and output pins of the package, and since each of the TLBRA and BAA is divided into a plurality of sections with respect to identification logical addresses, it is possible to attain the above reduction in the propagation delay as well as in the pin number even if those TLBRA and BAA are large in their capacity. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a buffer memory control apparatus; Fig. 2 is a block diagram illustrating a structure of a bipolar memory; and Fig. 3 is a block diagram illustrating an embodiment of the buffer memory control apparatus according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 3, an embodiment of the present invention will be described in detail hereunder. In the drawing, the numerals 1 - 31 attached to devices designate address bit positions and the numerals attached to lines designate the number of signal bits. Each region rectangularly encircled by a broken line is a region in which transfer of information can be made at a high speed. For example, one LSI may be such a region, which is represented as an LSI 60 and an LSI 70 in the following. The reference numerals 40 and more are used to designate other constituent parts. In Fig. 3, a logical address for instruction fetch or operand fetch is set in a logical address register LAR 40. The logical address is composed of 31 bits from bit 1 to bit 31. In an address translation buffer (TLB, 51, 61, 71), the directory of the logical address entries registered in the TLB is abbreviated to TLBLA, and a data portion in which real addresses are stored is abbreviated to TLBRA. A buffer address array for holding real addresses of the data held in a buffer memory is abbreviated to BAA (62, 72) and the buffer memory is abbreviated to BS (81). The logical address set in the LAR 40 is used to make an access to the TLB which is split into a TLBLA and two TLBRAs, the BAA, and the BS. The TSB has two rows the columns of which are identified with the bits 12- 19 of the logical address, while the BAA has 16 rows which are identified with the bits 18 - 24 of the logical address. Data of 16 rows are read out from the BS 81 and one of the data can be selected at a high speed if the TLBRA and BAA can be stored in one and the same LSI (with no inter-IC connection). If the TLBRA and BAA cannot be stored in one and the same LSI, it is necessary to divide the TLBRA and BAA into a plurality of sections so as to store the TLBRA and BAA in a plurality of LSIs. The present invention is intended to show a manner how to divide the TLBRA and BAA. In this embodiment, since the column identification addresses of the respective TLBRA and BAA are common or overlapped at the bits 18 and 19 and the columns of the respective TLBRA and BAA which are different from each other at these bits 18 and 19 are not identified at the same time, the TLBRA and BAA can be divided so as to obtain four combinations. In Fig. 3, each of the TLBRA and BAA is divided into two sections depending on the state of the bit 19, whether it is "1" or "0", and the sections 61 and 62 of the respective TLBRA and BAA, the bit 19 of each of which is identified with "0", is stored in the LSI 60 while the sections 71 and 72 of the respective TLBRA and BAA, the bit 19 of each of which is identified with "1", is stored in the LSI 70. An address bit line 69 from the LAR 40 is supplied to both the LSIs 60 and 70. The TLBRA sections 61 and 71 are identified with the logical address bits 12 - 18, while the BBA sections 62 and 72 are identified with the logical address bits 18, and 20 - 24. Read out real addresses are compared by comparators 63 and 73, and upon coincidence the respective row numbers are encoded in encoders 64a, 64b, 74a and 74b. One of the respective outputs of the encoders 64a, 64b, 74a and 74b is selected by a selector 80 in accordance with the combination of the value of the bit 19 of the logical address set in the LAR 40 and the value of the output of an encoder 53. When the value of the bit 19 of the logical address set in the LAR 40 is "0", the respective outputs of the encoders 74a and 74b are made invalid while when it is "1" the respective outputs of the encoders 64a and 64b are made invalid. When the TLBLA coincidence signal put out from the encoder 53 indicates the row 0, the respective outputs of the encoders 64b and 74b are made invalid, while when the TLBLA coincidence signal indicates the row 1, the respective outputs of the encoders 64a and 74a are made invalid. In response to the BAA coincidence signal selected by the selector 80, a selector 82 selects one of the 16 rows of outputs of the BS 81 and puts out the same as data of 8 bits. Fig. 3 shows a buffer memory control apparatus for instruction fetch or operand fetch. Also in the case of operand store, a circuit for judging into which one of the 16 rows of the BS 81 an operand is to be written is constituted on the basis of similar point of view to that described above. Further, when the logical address set in the LAR 40 has not been registered in the TLB, a real address corresponding to the logical address is obtained by well known means, the thus obtained real address is set in a real address register 41 (hereinafter abbreviated to "RAR"), and after determination of a row to be replaced by, for example, a least recently used (LRU) algorithm or the like, the bits 1 - 11 of the logical address are stored in that row of the column of the TLBLA 51 designated by the bits 12 - 19 of the logical address and the bits 1 - 19 of the real address set in the RAR 41 are stored in that row of the column of the TLBRA section 61 designated by the bits 12 - 18 of the logical address when the bit 19 of the logical address is "0" while stored in that row of the column of the TLBRA section 71 designated by the bits 12 - 18 of the logical address when the bit 19 of the logical address is "1". An address bit line 68 from the RAR 41 is supplied to both the LSIs corresponding to the bit line 69. When a block designated by a logical address set in the LAR 40 has not been registered in the BAA, the logical address is translated into a corresponding real address by using the TLB, the thus obtained real address is set in the RAR 41, and after determination of a row to be replaced by, for example, an LRU algorithm or the like, the bits 1 - 19 of the real address set in the RAR 41 are stored in that row of the column of the BAA section 62 designated by the bits 18 and 20 - 24 of the logical address when the bit 19 of the logical address is "0" while stored in that row of the column of the BAA section 72 designated by the bits 18 and 20 - 24 of the logical address when the bit 19 of the logical address is "1". A block designated by the logical address set in the LAR 40 is transferred to and stored in the BS 81.

Claims: A buffer memory control apparatus comprising: a buffer memory (81) for storing a part of information stored in a main storage; a buffer address array (BAA) storing respective main storage real addresses of data blocks stored in said buffer memory; an address translation mechanism (TLB) for translating a logical address into a real address when a memory access request at said logical address is made, said address translation mechanism being functionally divisible into a directory of logical address entries (TLBLA) and a directory of real address entries (TLBRA); comparator means (63, 73) for detecting coincidence between the real addresses produced by said address translation mechanism and the corresponding real addresses produced by said buffer address array; said logical address having a translatable portion (bits 1-19) actually supplied to said address translation mechanism, and another portion (bits 18-28) for directly addressing said buffer memory, said two portions of the logical address having a plurality of overlapping bits (bits 18, 19); said buffer memory control apparatus being characterized in that the logical address directory (TLBLA) and the real address directory (TLBRA) of said address translation mechanism are implemented on separate integrated circuits; said real address directory (TLBRA) and said buffer address array (BAA) are further divided into a plurality of real address storage portions (61, 71) and of buffer address sub-arrays (62, 72), respectively, whereby a correspondence is established between those real address storage portions and those buffer address sub-arrays being selected by the same state of at least one (bit 19) of said plurality of overlapping bits; corresponding ones (61, 62; 71, 72) of said real address storage portions and of said buffer address sub-arrays are implemented on the same integrated circuit (60; 70) together with the comparator means (63; 73) for detecting coincidence between the corresponding real addresses. A buffer memory control apparatus according to claim 1, further comprising selecting means (64, 74, 80, 82) connected to an output of said comparator means for selecting storage data of said buffer memory (81). A buffer memory control apparatus according to claim 2, in which said address translation mechanism includes a plurality of logical address directory portions (TLBLA, 51), and in which said buffer memory control apparatus further comprises a second comparator means (52, 53) for comparing an output of each of said plurality of logical address directory portions (TLBLA, 51) with a logical address, an output of said second comparator means being supplied to said selecting means (64, 74, 80, 82) so as to be used to perform the storage data selection.

Inventors: TANAKA ATSUSHI, WATANABE TSUYOSHI, TANAKA, ATSUSHI, WATANABE, TSUYOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1988
Main classification: G06F12
IPC codes: G06F12