Transfer control technique between two units included in a data processing system

In a data processing system comprising a central processing unit, a control store including a storage device, and an electrical bus for transferring information between said unit and said control store, the information including instructions generated by the central processing unit for controlling performance of operations by the control store, a response-control apparatus, included in said control store, comprising:

• A. means for receiving an instruction from said central processing unit by means of said bus, a said instruction capable of requesting the performance of one of several different operations by said control store, including a write instruction for writing information into said storage device and a read instruction for reading information from said storage device;
• B. decoder means for determining the operation indicated by said instruction;
• C. register means having a plurality of positions, including an end position;
• D. means, responsive to said decoder means, for placing indicia in at least one of said positions of said register means, said one of said positions dependent upon the operation indicated by said decoder means;
• E. means for stalling an operational response by said control store in response to said instruction until one of said indicia is in said end position;
• F. means, responsive to said means for stalling, for moving said indicia from said one of said positions to another one of said positions in a direction toward said end position each time said means for stalling dictates the operational response by said device;
• and
• G. means for providing the operation indicated by said instruction when one of said indicia is in said end position.

In a data processing system comprising a central processing unit, a data processing device and an electrical bus for transferring information between said unit and said device during periods of time granted to either said unit or said device as bus cycles, the information including instructions generated by the central processing unit for controlling the operation of said device and requests for the device to execute a transferred instruction, apparatus included in said device, comprising:

• A. register means having a plurality of positions, including a last portion, each of said positions having an input, and wherein said register means includes means for shifting indicia stored in said positions toward said last position;
• B. means, responsive to an instruction received from said unit, for storing said indicia in said positions included in said register means;
• C. means for executing an operation indicated by said received instruction if one of said indicia is stored in said last position;
• D. means for activating said means for shifting if none of said indicia is stored in said last position;
• E. means for indicating to said unit that a request to execute a said received instruction should be repeated during the next available one of said bus cycles if none of said indicia is stored in said last position;
• and
• F. means, responsive to a repeated request from said unit to execute said instruction, for enabling said means for activating or said means for executing depending upon the location of said indicia in said register means.

Apparatus comprising:

• A. a shift register having a plurlity of positions, including a last position, each of said positions having an input for receiving one of a plurality of signals, each said input coupled to receive a different one of said signals, each said signal associated with an operation to be performed by said apparatus;
• B. means for receiving one of said signals at said input of one of said positions which is not said last position and for storing indicia corresponding to said signals in said positions, said indicia also associated with an operation to be performed by said apparatus;
• C. means for shifting said indicia to others of said positions;
• D. means, responsive to said means for shifting, for delaying the performance of said operation associated with said shifted indicia by said apparatus for a period of time related to said operation;
• E. means for enabling said means for shifting to further shift said indicia to said others of said positions after said means for delaying has delayed the performance of said operation associated with said shifted indicia by said apparatus for said related period of time;
• and
• F. means, responsive to the shifting of one of said indicia to said last position for activating said apparatus to perform said operation associated with said indicia shifted into said last position.

In a data processing system comprising a first data processing unit, a second data processing unit including a shift register having a plurality of storage positions including a last position, and an electrical bus for transferring information between said first unit and said second unit during bus cycles which are short periods of time granted to either of said units for use of said bus, a machine-implemented process comprising the method steps of:

• A. issuing an instruction during a first bus cycle from said first unit to said second unit, said instruction indicating that said second unit perform a given operation;
• B. storing indicia representing said issued instruction in at least one of a plurality of said positions in said shift register, the position in which said indicia are stored being indicative of the type of said issued instruction;
• C. acknowledging during a next available one of said bus cycles from said second unit to said first unit, in response to the storage of one of said indicia in said last position, that said second unit has accepted and performed the operation indicated by said instruction represented by said indicia stored in said last position;
• D. requesting by said second unit that said first unit reissue to said second unit the request to perform the operation indicated by said issued instruction if the indicia representing said issued instruction are not stored in said last position;
• E. reissuing said request by said first unit;
• F. receiving during a next available one of said bus cycles said request reissued by said first unit to said second unit requesting said second unit to perform the operation indicated by said issued instruction;
• G. shifting, in response to said step of receiving, said indicia to another of said positions included in said register means in a direction toward said last position;
• and
• H. repeating said steps of requesting, receiving and shifting until one of said indicia is stored in said last position of said register means, following which said step of acknowledging is performed.