Priority selection system in access control

• US 3,967,249 A
• Filed: 12/30/1974
• Issued: 06/29/1976
• Est. Priority Date: 12/28/1973
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Taniyama, Yukio, Kanda, Kaoru, Nagahori, Tetsuo, Isaka, Tetsuo
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Chapnick, Melvin B.
• Application Number:
  US05/537,450
• Time in Patent Office: 547 Days
• Field of Search: 340/172.5
• US Class Current: 710/37
• CPC Class Codes: G06F 13/368 with decentralised access control

Abstract

A selection system for an information processing system wherein a unit, such as a magnetic tape unit, is shared by a plurality of control units. At least first and second signal lines are connected between each control unit at a driver circuit and a receiver circuit pair. The two signal lines connected between each control unit correspond to a single shared unit, and each control unit provides a driver circuit and a receiver circuit connected so as to transmit and receive signals carried on each line. Each line is connected to a separate driver circuit and receiver circuit at each control units. A block signal is transmitted from one of the control units through a first signal line to the other control units to prevent them from starting their operation for accessing the shared unit, and selection signals are transmitted from possible plurality of started control units through the second signal line at different timings to thereby determine priority of the started control units for accessing the shared unit. With this system, the control units can be correctly operated in accordance with priority by simple circuit construction without employing a scanning system, and further, the number of control units can be increased without increasing the cost of the selection system.

Claims

1. A selection system for an information processing system comprising in combination:

a shared unit;

a plurality of control units connected to said shared unit, for accessing said shared unit, wherein each of said plurality of control units includes means for generating a block signal when that corresponding control unit starts its operation, means for generating a reserved signal when said corresponding started control unit completes its operation and commences accessing said shared unit, and a time delay means connected to said block signal generating means for defining an operation time of said corresponding control unit from said start to said completion and controlling said reserved signal generating means, the respective time delay means of said plurality of control units defining respectively different operations times for each of said plurality of said control units;

a first signal line connected in common to each of said plurality of control units for conveying said block signals;

a second signal line connected in common to each of said plurality of control units for conveying said reserved signals;

each control unit, further including first transmitting means for transmitting a block signal generated by its corresponding block signal generating means, when said control unit has started its operation, over said first signal line to all other said control units, and first receiving means for receiving said transmitted block signals conveyed on said first signal line and preventing said corresponding control unit from subsequently starting its respective operation;

each control unit also includes second transmitting means for transmitting a reserved signal generated by its corresponding reserved signal generating means, when said control unit has completed its operation, over said second signal line to all other said control units, and second receiver means for receiving said transmitted reserved signals conveyed on said second signal line and preventing said corresponding control unit from completing its operation;

said selection system is characterized by the control unit having the shortest said operation time, of said plurality of control units which have been started, being the first to transmit a reserved signal, thereby preventing all others of said plurality of control units from completing their corresponding operations.

2. A selection system according to claim 1, wherein said time delay means includes a flip-flop circuit connected to receive said block signal from said corresponding block signal generating means.

3. A selection system according to claim 1, wherein said time delay means includes a single-shot multivibrator, having a different pulse generation delay time for each of said plurality of said control units and connected to receive said block signal from said corresponding block signal generating means.

4. A selector system for an information processing system of claim 1, wherein said shared unit is a magnetic tape unit and said plurality of control units are magnetic tape control units.

5. A selection system for an information processing system comprising:

a plurality of shared units;

a plurality of control units, each respectively connected to said plurality of shared units for accessing said shared units, wherein each control unit includes means for defining an operation time as the time duration from the start to completion of the accessing operation, a plurality of means for generating a blocking signal respectively corresponding to a different one of said plurality of shared units, means corresponding to said blocking signal generating means for generating a reserved signal, means corresponding to said blocking signal generating means for transmitting a blocking signal generated by said corresponding blocking signal generating means to the others of said plurality of said control units, means corresponding to said blocking signal transmitting means for receiving said transmitted blocking signal, means corresponding to said reserved signal generating means for transmitting a reserved signal generated by said corresponding reserved signal generating means to the others of said plurality of said control units, means corresponding to said reserved signal transmitting means for receiving said transmitted reserved signal;

a plurality of first signal lines respectively corresponding to said plurality of shared units, each of said first signal lines being connected to corresponding blocking signal transmitting means and blocking signal receiving means at each control unit;

a plurality of second signal lines respectively corresponding to said plurality of shared units, each of said second signal lines being connected to corresponding reserved signal transmitting means and reserved signal receiver means at each control unit;

wherein the output of each said blocking receiving means being connected to said corresponding blocking signal generating means to inhibit the generation of said blocking signal when said blocking signal receiving means receives a blocking signal from another control unit;

the output of each said reserved signal receiving means being connected to said reserved signal generating means to inhibit the generation of said reserved signal when said reserved signal generating means receives a reserved signal from another control unit;

further wherein, each said control unit, when starting its operation for accessing a given shared unit, causes the blocking signal generating means thereof corresponding to said given shared unit to generate a blocking signal and said corresponding blocking signal transmitting means to transmit said blocking signal on said corresponding first signal line to all other control units, thereby preventing other said control units from subsequently starting their respective operations for accessing said given shared unit; and

the corresponding reserved signal generating means, of each said control unit which has started its operation for accessing the said given shared unit;

generating a reserved signal at the end of the corresponding operation time for said control unit and said corresponding reserved signal transmitting means transmitting said reserved signal over said corresponding second signal line to all other control units, thereby preventing all other control units which have started their operation for accessing said given shared unit from completing their operations.

6. A selection system as in claim 5, wherein said shared units are magnetic tape units and said control units are magnetic tape control units.