AU580359B2 - Arrangement for apportioning priority among co-operating computers - Google Patents

Arrangement for apportioning priority among co-operating computers

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Publication number
AU580359B2
AU580359B2 AU50932/85A AU5093285A AU580359B2 AU 580359 B2 AU580359 B2 AU 580359B2 AU 50932/85 A AU50932/85 A AU 50932/85A AU 5093285 A AU5093285 A AU 5093285A AU 580359 B2 AU580359 B2 AU 580359B2
Authority
AU
Australia
Prior art keywords
priority
signal
bus
low
access
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
AU50932/85A
Other versions
AU5093285A (en
Inventor
Lars-Orjan Kling
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from SE8406312A external-priority patent/SE445861B/en
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of AU5093285A publication Critical patent/AU5093285A/en
Application granted granted Critical
Publication of AU580359B2 publication Critical patent/AU580359B2/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F13/00Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
    • G06F13/14Handling requests for interconnection or transfer
    • G06F13/36Handling requests for interconnection or transfer for access to common bus or bus system
    • G06F13/362Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control
    • G06F13/366Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control using a centralised polling arbiter
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F13/00Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
    • G06F13/14Handling requests for interconnection or transfer
    • G06F13/36Handling requests for interconnection or transfer for access to common bus or bus system
    • G06F13/362Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control
    • G06F13/364Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control using independent requests or grants, e.g. using separated request and grant lines

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Remote Monitoring And Control Of Power-Distribution Networks (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Description

ARRANGEMENT FOR APPORTIONING PRIORITY AMONG CO-OPERATING COMPUTERS
TECHNICAL FIELD
The invention relates to a priority apportioning arrangement for computers containing processors of two types, high-priority type which can determine its priority itself in relation to processors of the second low-priority type when using a common bus, such as to allow the use of the bus by the low-priority type also, if the high-priority processor does not have important tasks.
BACKGROND ART
In a system having several processors using the same bus where none of the processors has priority, distribution on the bus can take place with the aid of a ' logic which obtains a signal from each of the prospective users and assigns the bus to them in a given order, with the latest user coming last. None of the processors can be kept out longer than for a number of accesses corresponding to the number of processors minus one.
Apportioning becomes more complicated when a number of processors with low priority and a processor with high priority work on the same bus. In known arrangements, such as that described in Electronic Design, May 24th, 1978 an extra time is necessary for assigning the bus when the high-priority processor needs it.
DISCLOSURE OF INVENTION
The object of the invention is to shorten the waiting and to give the high- priority processor full priority when it needs the bus, but to give access to the low-priority processors when the bus is not needed by the high-priority processor. This is achieved in accordance with the invention by access to the bus being blocked for the low-priority units when the high-priority one needs the bus, whereas when the high-priority unit does not need the bus immediately, the low-priority units are given access for a time in given proportion to the operating time of the high-priority unit. The invention is characterized as will be seen from the claim.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described below with the aid of an embodiment and with reference to the accompanying drawings, on which
Figure 1 is a block diagram of a processor system with processors working over a common bus,
Figure 2 is a block diagram of a priority distribution arrangement in accordance with the invention, and
Figure 3 is a time chart illustrating how the bus is assigned when the high- priority processor does not need the bus immediately
BEST MODE FOR CARRYING OUT THE INVENTION
According to Figure 1 a processor 1 with high priority is connected via a bus 2 to a plurality, in all eight, of low-priority processors 3a- 3h. A memory 4 is connected to the bus, and the processors have acess to the memory via the bus. The problem occuring in this co-operation is that access for the high-priority processor must always be ensured, while the low-priority processors share the remaining access time. In accordance with the invention this is solved by the priority apportioning arrangement denoted by 5. The arrangement is indicated as a separate unit, but may be divided such that certain parts are in the processors. The signals with which these units communicate with each other will be explained in detail in connection with Figure 2. Their designations are as follows:
BMA = bus master address. Selects one of the 8 low-priority processors. EBG = external bus grant. Grants access to one of the low-priority units. MBG = intensive processor bus grant. Grants access to the high-priority processor. RQB = request bus. Request for bus access from the low-priority units.
REB = reserve bus. Request for access to the bus from the high-priority processor.
BOC = bus occupied. The bus is engaged, work is in progress. Figure 2 illustrates the priority apportioning arrangement in the form of a block diagram. The mutual apportioning of the bus between the low-priority pro¬ cessors takes place with the aid of a logic consisting of a PROM memory 10 and a register 11. Each low-priority processor 3a-3h, in all eight according to the exemplified embodiement, sends a signal RQB with a request for access to the PROM memory 10, which contains a table. In the table there is given the address to that of the low-priority processors which shall be activated next. The address is pointed out by a signal BMA which enables addressing eight different units via a 3-wire line. The fed-out address is registered in the register 11 and points out in the memory a new address which is to be used when the next low- priority processor sends an RQB signal. Of the low-priority units only the unit 3h is indicated in detail. A wait flip-flop denoted by 6 has its output activated when bus access is desired according to the programme, and an access flip-flop is denoted by 7, this flip-flop being activated when the processor has obtained access, and is kept activated as long as this processor uses the bus. During this
' time the flip-flop sends the signal BOC denoting that the bus is engaged by the processor. The flip-flop 7 is activated by a comparator 8 determining that the address BMA sent from the register 11 agrees with the address of the processor itself and activates an input on an AND circuit 9, which obtains an EBG signal on another input, denoting that the bus is available for the low-priority processors. Such an arrangement is already known.
If it is now desired to subdivide the access between the low-priority processors and the high-priority processor such that the former will have access to the bus during a time which is in a given proportion to the time during which the high- priority processor uses the bus, although permitting the high-priority processor to have immediate access to the bus at any time, an arrangement in accordance with the invention is then necessary. The arrangement includes a first logic circuit 20 controlling the assignment of the bus alternatively to the high- priority unit or to a low-priority unit, and a second logic circuit 40, the output signal of which indicates that the high-priority unit is in immediate need of the bus or that it can temporarily release the bus to a low-priority unit. According to the exemplified embodiement, the first logic circuit 20 is arranged outside the processors while the second logic circuit 40 is in the high-priority processor. However, where the logic circuits are situated has no importance from the inventive aspect. The first logic circuit 20 has three inputs, a first where a signal RQB occurs when one of the low-priority units needs the bus, a second where a signal REB occurs when the high-priority unit needs the bus and a third where a signal BOC occurs denoting that the bus is engaged by one of the units. The signals on the first and the second inputs are taken to an AND circuit 21 which sends an output signal only if the high-priority unit does not request access, and is blocked for the opposite case. This signal is fed to an input on an AND circuit 22 the negation input of which obtains the signal BOC. When the signal BOC thus ceases in connection with the bus being disengaged and the signal REB does not occur since the high-priority unit is not in immediate need of the bus, an EBG signal is se it to enable access for one of the low-priority units. A further AND circuit 23 is arranged, which obtains the AND circuit 21 output signal on one side and the BOC signal on the other side. If both these signals cease, the signal MBG is generated, which assigns the bus to the high-priority unit and this signal is fed to the second logic circuit 40.
A program selector denoted by 30 provides one of two alternative signals in response to the programme in progress. The first type of signal from the programme selector signifies that immediate bus access is desired by the high- priority unit, and the other signal signifies that immediate access is desired, but low-priority units are also permitted to use the bus. A wait flip-flop denoted by 41 has its output activated immediately when the first type of signal is fed to its activating input S. The output signal blocks the circuit 21 so that access to the bus from the low-priority units is prevented, and when the (bus occupied) signal BOC ceases, the bus is once again assigned to the high-priority unit by the signal MGB. This is fed to one input of an AND circuit 39, the other input of which obtains the programme selector signal via an OR circuit 38. The output signal of the AND circuit 39 activates an access flip-flop 42, which feeds a BOC signal via its output to the logic circuit 20 to indicate that the bus is occupied. If the first type of signal remains from the programme selector, the output of the wait flip-flop 41 is immediately activated so that the circuit 21 is kept blocked and no EBG signal is sent for giving access to the low-priority units. The other type of signal from the programme selector 30 signifies that the high-priority unit can allow access for a low-priority unit. A flip-flop 43, which is activated by this signal, feeds a signal to the input of and AND circuit 6 in which a negation input is connected to the output of the flip-flop 42 so that it is blocked the whole time the high-priority processor uses the bus. The output of the AND circuit 46 is connected to an input of the OR circuit 47 which will send the output signal of the circuit 46 to the AND circuit 21. By activating the output signal of the circuit 46, and the generation of the REB signal taking place with a given delay after the BOC signal has ceased, due to the delay circuit 48, the REB signal does not occur until after the EBG signal has occurred at the output of the circuit 22, so that one of the low-priority units will be given access. The REB signal occurs, immediately afterwards which ensures that the high-priority unit is given direct access when the "bus occupied" signal BOC has ceased.
This is further explained in the time chart according to Figure 3. When the high-priority unit is working and there is no immediate need to use the bus again, there is no standing REB signal from the flip-flop 41. When the "bus occupied" signal BOC ceases, the output of the circuit 46 is activated with a ' time lag such that the REB signal does not occur until the EBG signal has had time to be sent to the low-priority processors. Immediately afterwards the circuit 21 is once again blocked by the REB signal, so that when the low- priority unit has completed its task and the BOC signal has ceased, the high- priority unit can take over the bus without delay. By the BOC signal ceasing, the register 11 is activated and the identity of the low-priority unit can be sent out. With the aid of the described arrangement it will be possible to assign the bus to the low-priority units during such periods where the program does not make necessary immediate acces for the high-priority unit, although it is ensured that the high-priority unit always has immediate access to the bus when so required.

Claims (1)

  1. CLAIM
    Arrangement for apportioning priority for computers that contain processors of two types, a high-priority type which can itself determine its priority in relation to processors of a second low-priority type when using a common bus, such as to allow the low-priority type to use the bus also, if the high-priority processor does not have important tasks characterized in that the arrangement includes a first and a second logic circuit, the first logic circuit (20) having three inputs, the first for an input signal (RQB) which signifies a request for access from one of the low-priority units (3a-3h) the second for an input signal (REB) which signifies a request for access from the high-priority unit (1) and the third for an input signal (BOC) which occurs during the whole time the bus is used, the circuit (20) having two outputs on which a signal (EBG) occurs on the first one for assigning the bus a low-priority unit (3a-
    ' 3h) if only the first input has been activated, on the second output there occuring a signal (MGB) for assigning to the bus the high-priority unit, while the signal on the first output is inhibited, the second logic circuit (40) being with two outputs and two inputs, a first output which feeds the signal (REB) with the request for access from the high-priority unit to the second input of the first logic circuit, and a second output which feeds the signal (BOC) indicating that the bus is occupied, to the third input of the first logic circuit, there occuring a signal (REB) unconditionally on the first input on its activation, the signal (REB. denoting on the second input of the first logic circuit that the high-priority unit desires access, so that the assigning or granting signal (MGB) occurs on the second output of the first logic circuit, the second input of the second logic circuit on activation resulting in that the signal (REB) of a request for access for the high-priority units occurs with delay on the first output of the second logic circuit so that the signal (EBG) for granting or assigning the bus to a low- priority unit has time to occur, but the high-priority unit still has immediate access to the bus after termination of the work of the low-priority unit.
AU50932/85A 1984-12-12 1985-11-01 Arrangement for apportioning priority among co-operating computers Ceased AU580359B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE8406312A SE445861B (en) 1984-12-12 1984-12-12 PRIORITY DISTRIBUTION DEVICE FOR COMPUTERS
SE8406312 1984-12-12
PCT/SE1985/000429 WO1986003606A1 (en) 1984-12-12 1985-11-01 Arrangement for apportioning priority among co-operating computers

Publications (2)

Publication Number Publication Date
AU5093285A AU5093285A (en) 1986-07-01
AU580359B2 true AU580359B2 (en) 1989-01-12

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Family Applications (1)

Application Number Title Priority Date Filing Date
AU50932/85A Ceased AU580359B2 (en) 1984-12-12 1985-11-01 Arrangement for apportioning priority among co-operating computers

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Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4787033A (en) * 1983-09-22 1988-11-22 Digital Equipment Corporation Arbitration mechanism for assigning control of a communications path in a digital computer system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU524538B2 (en) * 1978-11-06 1982-09-23 Honeywell Information Systems Italia S.P.A. Bus address control unit with priority selecting
AU525374B2 (en) * 1980-07-11 1982-11-04 Siemens Aktiengesellschaft Two-computer data block transfer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU524538B2 (en) * 1978-11-06 1982-09-23 Honeywell Information Systems Italia S.P.A. Bus address control unit with priority selecting
AU525374B2 (en) * 1980-07-11 1982-11-04 Siemens Aktiengesellschaft Two-computer data block transfer

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Publication number Publication date
AU5093285A (en) 1986-07-01

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