Apparatus for controlling system accesses having multiple command level conditional rotational multiple port servicing priority hierarchy

• US 4,821,177 A
• Filed: 09/02/1986
• Issued: 04/11/1989
• Est. Priority Date: 09/02/1986
• Status: Expired due to Fees

• Current Assignee: Honeywell Information Systems, Inc. (Honeywell International Inc.)
• Original Assignee: Honeywell Bull Incorporated
• Inventors: Rabins, Leonard, Koegel, Robert J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/902,545
• Time in Patent Office: 952 Days
• Field of Search: 364/200 MS File, 364/900 MS File
• US Class Current: 711/149
• CPC Class Codes: G06F 13/18 based on priority control G06F13/1605 takes precedence

Abstract

The apparatus controls access to at least one subsystem in response to requests for access from a plurality of equipments operatively connected to a corresponding port of said apparatus. The requests for access have a plurality of command levels wherein the command levels have a fixed predetermined priority relative to each other. The apparatus comprises a plurality of port request control elements for generating a plurality of specific request signals including a command level request signal to indicate the command level of a request received from the corresponding equipment, and a go signal to indicate the availability of the apparatus and the subsystem in order to execute the command requested. An activity priority select control element receives the specific request signals, and processes the go signals from each of the port request control elements to grant access within a predetermined time period to the equipment connected to the port having the highest port priority within the highest command level. There is also included logic which maintains a table of port priority for each command level utilized to determine a port priority within a command level. The table of port priority corresponding to the command level which was granted access is conditionally rotated when an equipment is granted access.

Claims

1. A data processing system comprising:

memory subsystem means for executing memory activities;

a system control unit (SCU) subsystem means having a plurality of ports;

a plurality of data handling units, each data handling unit being operatively connected to only one of said plurality of ports each data handling unit including means for producing and applying to its associated port a request signal set when the unit needs to access the memory subsystem means to request the memory subsystem means to execute a memory activity;

each request signal set requesting access to the memory subsystem means includes a command portion specifying a memory activity to be executed and a command priority portion specifying a priority for each such command;

said SCU subsystem means being operatively connected to the memory means for granting a data handling unit access to the memory means in response to the data handling unit producing a request signal set requesting such access, each port of the SCU subsystem means having a port priority for each command priority;

port request control means for each port connected to a data handling unit responsive to receiving a request signal set for generating port request control signals, the port request control signals including a port request go signal if the memory subsystem means and SCU subsystem means are available to execute the command portion of the signal set received by the port from its associated data handling unit; and

activity priority select means of the system controller operatively connected to each port of the system controller to receive said port request control signals generated by the port request control means of each port, said activity priority select means for producing and transmitting to a selected port a port request granted signal, the selected port being the port applying a port request go signal to said priority select means, and the command portion of the request signal set applied to the selected port having a higher command priority than that of any other port applying a port request go signal to the priority select means; and

if two or more ports apply a port request go signal to said priority select means during the same time period having the same command priority, the port selected is the port having the highest port priority, the port request granted signal is transmitted to the selected port enabling the memory subsystem means to execute the memory activity specified by the command portion of the request signal set applied to the selected port.

2. A data processing system as defined in claim 1, in which the memory subsystem means includes a plurality of addressable memory modules, and each request signal set requesting a memory activity includes the address of the memory module the unit requests execute the memory activity;

said port request control means generating a port request go signal if the addressed memory module is available to execute the requested memory activity.

3. A data processing system as defined in claim 2, in which a bus interconnects the SCU subsystem means and the modules of the memory subsystem means, said port request control means producing a port request go signal if the bus is available when needed in executing the requested activity.

4. A data processing system as defined in claim 2, in which the priority level assigned to each command is fixed.

5. A data processing system as defined in claim 4 in which the priority of each port for each command level is changeable.

6. A data processing system as defined in claim 5, in which for a given command priority level tee port priority of each of the ports changes each time the port having the highest port priority for the command priority level pending at any given period of time receives a port request granted signal.

7. A data processing system as defined in claim 6, in which at least one of the data handling units is an I/O controller.

8. A data processing system as defined in claim 7, in which at least one of the data handling units is a central processor.

9. A data processing system as defined in claim 8, in which the number of command priority levels is two.

10. The data processing system of claim 9 in which the SCU subsystem means includes means for rotating the priority of the ports for a given command priority each time a port requesting a memory access and having the highest port priority for said command priority pending during said given period of time is granted access to the memory means.

11. The method of controlling access to a random access memory capable of executing memory activities by a plurality of data handling units of a data processing system, each data handling unit being connected respectively to a corresponding port of a system controller, wherein a data handling unit requesting access to the random access memory issues a request including a command for a given memory activity to the system controller, said method comprising the steps of:

assigning a priority to each command issued by each data handling unit;

assigning a port priority to each port of the system controller for each command priority;

determining the availability of the random access memory to execute a memory activity in response to the command issued by each data handling unit and the availability of the system controller during a predetermined period of time; and

granting to a selected port and its associated data handling unit access to the random access memory during said predetermined period of time, the port selected satisfying the following criteria;

one, the random access memory is available to execute the memory activity of the command of the access request, and the system controller is available to provide the unit access to the memory;

two, the priority assigned to the command of the access request assured by the data handling unit of a port satisfying the first criteria is the highest pending during said predetermined period of time; and

three, if the access requests of two or more units pending at the same time both satisfy the first criteria and have commands of the same priority and that priority is the highest of any of the requests satisfying the first criteria pending at that time, the port selected is the port having the highest port priority for that command priority at that time.

12. The method of claim 11 which includes the additional step of rotating the port priorities of the ports for a given command priority when the port having the highest port priority for that command level pending during said predetermined period of time is granted access to the memory by the system controller.