Information processor comprising a write buffer circuit containing an address buffer and a data buffer corresponding to each other

• US 5,404,480 A
• Filed: 03/19/1992
• Issued: 04/04/1995
• Est. Priority Date: 04/04/1991
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Suzuki, Hiroaki
• Primary Examiner(s): Dixon, Joseph L.
• Assistant Examiner(s): Asta, Frank J.
• Application Number:
  US07/853,940
• Time in Patent Office: 1,111 Days
• Field of Search: 395/425, 364/200 MS File, 364/900 MS File, 365/189.07
• US Class Current: 711/117
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence

Abstract

The invention assures data consistency at a time of data update. Also, the invention results in a reduction in the access time required to store incoming data. In response to an equality signal from a comparator circuit of a write buffer circuit which is then in an active level, data is immediately read out from a data buffer store having an address corresponding to the equality signal. A unidirectional tristate buffer is provided for temporarily disconnecting an address bus extending between a CPU and the write buffer circuit, again when such equality signal is in an active level. Similarly, a bidirectional tristate buffer is provided for temporarily disconnecting a data bus extending between the CPU and the write buffer circuit. At times a local controller may take over command of buffer storage of data, with an interrupt of the local controller if the central processor seizes command.

Claims

1. A information processor comprising a central processing unit, a main memory coupled to said central processing unit via a bus, said central processing unit issuing a data-write request with a transfer of a write-data to be written into said main memory and thereafter issuing a data-read request to fetch said write-data from said main memory, and a write buffer circuit coupled to said bus for temporarily storing said write-data, whereby said write data is not immediately stored in said main memory, said write buffer circuit performing a data-write operation to said main memory in place of said central processing unit in order to write said write-data into said main memory while said bus is free from said central processing unit said write data being deleted from said write buffer circuit after said write data is written into said main memory, and said write buffer circuit returning said write-data to said central processing unit in place of said main memory when said central processing unit issues said data-read request before said write buffer circuit writes said write-data into said main memory.

2. The information processor as claimed in claim 1, wherein said write-data is read out from said main memory and is transferred to said central processing unit when said data-read request is issued after said write buffer circuit writes said write-data into said main memory.

3. A central information processing unit comprising, a main memory coupled to said central information processing unit via a bus, said central information processing unit transferring over said bus a write-address to be used for accessing an address of said main memory and a write data to be written into said address of said main memory, and a write control buffer circuit coupled to said bus in order to temporarily store said write-address and said write-data received from the central information processing unit and to perform a data-write operation to said main memory said write-data is not immediately stored in said central processing unit in order to write said write-data into said address of said main memory in response to a use of said write-address, said write-data and said write-address being deleted from said write control buffer after said write-data is written into said main memory, said central processing unit issuing a data-read request by transferring a read address over said bus to fetch a read-data from said main memory, and said write control buffer circuit returning said write-data to said central processing unit as said read-data, whereby said write-data had not been stored in said main memory and said read-address is coincident with said write-address which is still stored in said write buffer circuit.

4. An information processor comprising a CPU, a main memory for storing data corresponding to addresses supplied from said CPU in a write mode, supplying data a corresponding to addresses supplied from said CPU in a read mode, a write buffer circuit for temporarily storing data and addresses which are thereafter to be stored in said main memory wherein said write buffer circuit supplies stored data to said main memory independently of said CPU operation and does not continue to store said data after supplying said data in said write mode, said write buffer circuit supplying a data to CPU when said write buffer circuit is storing said data which has been requested by said CPU in said read mode.

5. An information processor claimed in claim 4, said write buffer circuit including a data buffer circuit comprising a plurality of address buffer stages for storing said addresses, a comparator circuit having a plurality of individual comparator stages for comparing inputted addresses with addresses stored in said respective address buffer stages and for outputting equality signals having an active level in response to said comparator stages finding a coincidence between said inputted and stored addresses, and a plurality of individual data buffer stages individually corresponding to said respective address buffer stages.

6. An information processor claimed in claim 5, said write buffer circuit further including an output stage pointer for storing an address corresponding to an address which said comparator finds when said equality signal is in said active level, whereby data is read out of said data buffer circuit in response to the content of said output stage pointer means.