JP2000148668A - Bus arbitration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable bus arbitration, wherein the standby permissible time of each bus master is not exceeded by comparing 'occupation expected times when the bus use right is obtained' by bus masters with 'standby permissible times, when the bus use right cannot be obtained' and giving the bus use right to only a bus master which does not exceed the standby permissible times of other bus masters. SOLUTION: An arbitration part 60 arbitrates common bus requests from bus masters 10, 20, and 30 and allows a proper bus master to use a common bus according to the situation. Timers 11, 21, and 31 measure the standby permissible times of the respective bus masters. Then the 'occupancy expected times when the bus use right is obtained' by the bus maters 10, 20, and 30 are compared with the 'standby permissible times when the bus use right cannot be obtained' to carry out bus arbitration, so that a data transfer interrupt request to a bus master once given the bus use right is not generated and the standby permissible times of other bus masters are not exceeded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to arbitration of the right to use a bus when a plurality of bus masters are connected to a shared bus when each bus master uses the bus.

[0002]

2. Description of the Related Art In conventional bus arbitration, priorities are determined in advance, and when a bus request from each bus master occurs simultaneously, a bus user is determined according to the priority. . If the priority is fixed, there may be a case where a lower-ranking bus master cannot permanently acquire the right to use the bus. Alternatively, there is a method of equalizing the opportunity to acquire the bus right, such as lowering the priority of the bus master to the lowest order every time any bus master acquires the bus use right. In many cases, bus masters with different bus occupation periods and waiting time limits when bus rights are acquired are connected, so it is most efficient for the entire system to equalize the bus right acquisition opportunities. I can't say that there is. Rather, arbitration in accordance with the circumstances of each bus master is efficient.

As means for solving the problem, Japanese Patent Laid-Open No. 9-2
Japanese Patent Application Publication No. 31165 discloses a bus arbitration control system in which the size of transfer data of a bus cycle and occupation time data are added as additional information at the time of a bus request, and a bus right is given to the bus master based on the additional information. It is proposed to estimate the bus occupation period in such a case, and to give the bus right preferentially from a bus master having a short occupation period, thereby reducing the total standby time of the entire system.

On the other hand, in Japanese Patent Application Laid-Open No. 9-91247, the "standby time" for each bus master is set in the bus arbitration unit.
Arbitration is performed by giving priority to the bus master with a short remaining allowable time, or in some cases, requesting the bus master holding the bus right at that time to give up the bus right. Propose that.

[0005]

Problems to be Solved by the Invention
In the proposal of JP-A-5, too much priority is given to the efficiency of the entire system, and it does not take into account the tightness of each bus master who has requested the use of the bus. The proposal in Japanese Patent Application Laid-Open No. 9-91247 gives too much priority to the tightness of the bus master and does not consider the efficiency of the entire system. Also, in order to rescue the bus master performing the real-time processing, the bus master using the bus is requested to relinquish the bus right at a certain point in time, but it is up to the bus master to determine whether to relinquish the bus right. There is no guarantee that they will give up. The bus master is
It is also conceivable that the specification may not be able to cope with the request for interruption of the data transfer. In such cases, the allowable standby time is exceeded and the real-time processing is impaired.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art. JP-A-9-23
A bus right is arbitrated based on information on data transfer of each bus master as in Japanese Patent Application Laid-Open No. 1165, to optimize the efficiency of the entire system, and a timer for measuring an allowable standby time as in Japanese Patent Application Laid-Open No. 9-91247. Prepared and furthermore, "Scheduled occupation time when bus use right is obtained" for each bus master
Is compared with the "allowable time when the bus use right is not obtained" so as not to exceed the wait allowable time of other bus masters without generating a data transfer interrupt request to the bus master once granted the bus use right. By having a mechanism for performing bus arbitration taking into account the above, reliable and efficient bus arbitration is performed without delaying real-time processing. According to the first aspect of the present invention, a shared bus, a plurality of bus masters that occupy the bus and perform data transfer, and a bus master to which a bus right is granted by arbitrating a bus request signal from the bus master are exclusively used. A bus arbitration unit to select, in the bus arbitration system, the bus master includes a unit for registering various information on data transfer in the bus arbitration unit, and when a bus request from the plurality of bus masters overlaps, The arbitration unit includes means for calculating the efficiency of the entire system based on the registered information and selecting a bus user.The bus arbitration means receives a bus request from a bus master having a high need to perform real-time processing, When competing with a bus request from another bus master, the "maximum standby time" of the bus master requiring real-time processing is Compare the "scheduled time to occupy the shared bus" calculated from the registered information of the master, and if it is determined that the bus master requiring real-time processing is pending and the real-time processing is impaired, Means for giving the right to use the shared bus preferentially. Claim 2
According to the invention described in the above, a shared bus, a plurality of bus masters that occupy the bus and perform data transfer, and a bus that arbitrates a bus request signal from the bus master and exclusively selects a bus master to which a bus right is granted In the bus arbitration system, comprising: an arbitration unit, each of the bus masters described above includes means for transmitting various information related to its own data transfer to the bus arbitration unit,
When bus requests from a plurality of bus masters overlap, the bus arbitration unit calculates the efficiency of the entire system based on various information of data transfer transmitted together with the bus requests from each bus master and selects a bus user. The bus arbitration means is provided, when a bus request from a bus master that needs to perform real-time processing conflicts with a bus request from another bus master, the “maximum standby time of a bus master requiring real-time processing” And the "scheduled time to occupy the shared bus" calculated from information transmitted by a bus master other than the bus master together with the bus request, and as a result, it is determined that the bus master requiring real-time processing is pending and the real-time processing is impaired Priority is given to the bus master who needs real-time processing. Comprising means, it is characterized in that. According to a third aspect of the present invention, a shared bus, a plurality of bus masters that occupy the bus and perform data transfer, and a bus master that arbitrates a bus request signal from the bus master and grants a bus right are exclusively selected. In the bus arbitration system including the bus arbitration unit, each of the bus masters includes a unit that transmits information that does not change among various information related to its own data transfer to the bus arbitration unit and registers the information in the bus arbitration unit. The bus master includes means for transmitting only information that changes for each bus request to the bus arbitration unit, and when bus requests from a plurality of bus masters overlap, the bus arbitration means uses the information registered in the bus arbitration unit and the bus arbitration unit. The "scheduled time to occupy the shared bus" is calculated from the data transfer information transmitted along with the request, and the "bus standby state" of the bus master requiring real-time processing is calculated. Compared to a long time ", it is characterized in that it comprises means for arbitrating.

[0007]

An embodiment of the present invention will be described below with reference to FIG. The bus masters 10, 20, 30 are connected to the shared bus and request to occupy the shared bus. The arbitration unit 60 includes the bus masters 10, 20,
The arbitration unit arbitrates a shared bus request from the server 30 and permits an appropriate bus master to use the shared bus depending on the situation. The timers 11, 21, 31 measure the permissible standby time of each bus master. The internal information 12, 22, 32 is a part for storing information such as the transfer frequency and scale of each bus master inside the arbitration unit 60. Reference numerals 101, 201 and 301 are signals indicating the intention of a shared bus request from each bus master. 102,202,3
02 is information accompanying the shared bus request from each bus master, and is a portion that changes every time it is transferred, and is updated by the bus master as necessary. Reference numerals 103, 203, and 303 denote information on the permissible standby time from timers provided for each bus master. 104, 204, 304 Information accompanying the shared bus request from each bus master, which does not change with each transfer and is set in advance. 111,
112, 113 These signals are exclusively valid and indicate that the arbitration unit has permitted the use of the shared bus to the validated connection destination bus master.

There are many algorithms for evaluating the internal information and the accompanying information and selecting a bus master so that the shared bus is used efficiently.
The basic policy is to minimize the total standby time of all bus masters used in "1165 publication". For a description of the benefits of mediation under this policy, see
No. 31165 ".

Next, the operation of the embodiment of the present invention will be described with reference to FIG. First, regarding the bus master 10,
The estimated occupation time when the right to use the bus is granted is calculated from the internal information 104 and the accompanying information 102, and a 3T period (T is a unit of time. In the description of the present invention, a reference representing a relative time length) ). This value can be estimated with higher accuracy by increasing the elements required for calculation, such as the planned transfer data amount, the effective bus width, and the response of the data transfer destination. Similarly, it is assumed that the scheduled occupancy period of the bus master 20 is 5T and the scheduled occupancy period of the bus master 30 is 7T.

On the other hand, as for the bus master 10, it is assumed that the maximum allowable time from when a bus request is generated to when the right to use the bus is obtained and data transfer is permitted is 10T. This value is determined by restrictions specific to each application, such as when the bus master is a device that communicates with the outside or a controller of a storage device, and the buffer performance of the bus master itself. Similarly, the bus masters 20 and 30 are 20T and 6T. These standby allowable times start counting down from the time when a bus request is generated, and when they reach 0T, the real-time processing of the bus master is impaired. A certain time T
Assume that bus request signals 101, 201, and 301 from the bus masters 10, 20, and 30 simultaneously occur at 0 and conflict with each other. The selection that minimizes the total waiting time of all bus masters is to give priority to a bus master with a short bus occupation period over a bus master with a long bus occupation period.
First, the validity is examined with the bus master 10 having the shortest bus occupation period of 3T as a candidate. The scheduled data transfer end time of the bus master 10 is the time T0 + T3 after the scheduled transfer time 3T of the bus master 10 from the time T0.
It is.

The bus master 20, which is assumed to be postponed,
30 are 17T (= 20T−3T) and 3T (= 6T−3T), respectively, the allowable standby time at time T0 + 3T, and do not reach 0T. Therefore, there is no problem even if the bus right is given to the candidate bus master 10. It can be confirmed that there is no. The bus master 10 is given a bus right as assumed, and the bus master 10 occupies the bus and ends the data transfer, and the time T0 +
It reaches 3T.

Next, the validity of the remaining two bus masters will be examined with the bus master 20 having a shorter bus occupation period of 5T as a candidate. The scheduled data transfer end time of the bus master 20 is the time T0 + 8T after the scheduled transfer time 5T of the bus master 20 in addition to the time T0 + 3T. However, the bus master 30, which is assumed to be turned later,
The standby permissible time at time T0 + 8T is -2T (= 6T-
8T), and if the right to use the bus is given to the bus master 20 as it is, the standby allowable time of the bus master 30 will be exceeded. However, when the bus master 30 is considered as a candidate, the data transfer end time of the bus master 30 is the time T0 + 10T after the scheduled transfer time 7T of the bus master 30 from the time T0 + 3T. In this case, the time T0 of the bus master 20 assumed to be postponed
The allowable standby time at + 10T is 10T (= 20T−10).
T), it can be determined that there is no problem even if the right to use the bus is given to the candidate bus master 30. After all, in this case,
By granting the bus use right in the order of the bus master 10, the bus master 30, and the bus master 20, arbitration with the shortest total standby time was performed under the condition that the allowable standby time of any bus master was not exceeded. What is important here is to verify the effect on the bus master that is passed after the candidate bus master, assuming that the candidate bus master has obtained the bus right and the occupied occupation time has elapsed before actually granting the bus right. It is to be. Indeed, even if only the efficiency at that time is emphasized and the bus right is handed over in a short-circuit, depending on the specifications of the bus master, the data transfer is interrupted later by the instruction of the arbitration unit, and the allowable waiting time is In some cases, it may be possible to transfer the bus right to a tight bus master. However, according to the present invention, the central bus arbitration control unit does not rely on the bus master's data transfer interruption specification. It is possible to guarantee that the time will not be exceeded.

[0013]

As described above, according to the bus arbitration method of the present invention, the most efficient arbitration for the entire system is usually performed, and at the same time, the evaluation is performed by incorporating the allowable waiting time of each bus master. By not giving the right to use the shared bus to the bus master that exceeds the allowable waiting time of another bus master, it is possible to perform bus arbitration that does not exceed the allowable waiting time of each bus master.

Depending on the system configuration, it may not be possible to prevent all bus masters from exceeding the allowable waiting time, regardless of the order in which the bus rights are transferred, but this is because the shared bus is inherently provided. There are cases where the bus masters are excessively connected ignoring the transfer performance limit that is present, the bus masters have an extremely short waiting time, or the bus masters have a very long bus occupation time. This is out of the scope of the effect of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating one embodiment of a bus arbitration system of the present invention.

[Description of Signs] 10 Bus master 20 Bus master 30 Bus master 60 Arbitration unit 61 Arbitration control unit 11 Timer 21 Timer 31 Timer 12 Internal storage unit of arbitration unit 22 Internal storage unit of arbitration unit 32 Internal storage unit of arbitration unit 101: shared bus request signal 201: shared bus request signal 301: shared bus request signal 102: information associated with shared bus request 202: information associated with shared bus request 302: associated with shared bus request Information 103: information on allowable waiting time 203: information on allowable waiting time 303: information on allowable waiting time 104: information associated with shared bus request 204: information associated with shared bus request 304: information associated with shared bus request 111 ... shared bus use permission signal 211 ... shared bus use permission signal 311 ... shared bus use permission Signal

Claims (3)

[Claims] 1. A shared bus, a plurality of bus masters that occupy the bus and transfer data, and a bus arbitration that arbitrates a bus request signal from the bus master to exclusively select a bus master to which a bus right is granted. A bus unit, wherein each of the bus masters has means for registering various information related to data transfer in a bus arbitration unit, and when bus requests from the plurality of bus masters overlap,
The bus arbitration unit includes means for calculating the efficiency of the entire system based on the registered information and selecting a bus user. The bus arbitration means receives a bus request from a bus master that needs to perform real-time processing. When conflicting with a bus request from another bus master, the "maximum waiting time" of the bus master requiring real-time processing and the "scheduled time for occupying the shared bus" calculated from the registration information of the bus master other than the bus master concerned And, if it is determined that the bus master requiring real-time processing is pending and the real-time processing is impaired as a result, means for preferentially giving the right to use the shared bus to the bus master requiring real-time processing should be provided. Features a bus arbitration system. 2. A bus arbitration for exclusively selecting a shared bus, a plurality of bus masters occupying the bus and performing data transfer, and arbitrating a bus request signal from the bus master to select a bus master to which a bus right is granted. The bus master includes means for transmitting various information on its own data transfer to the bus arbitration unit, and when bus requests from a plurality of bus masters overlap, the bus arbitration unit The bus arbitration means includes means for calculating the efficiency of the entire system based on various information of data transfer transmitted along with the bus request and selecting a bus user. The bus arbitration means includes a bus from a bus master which needs to perform real-time processing. When a request conflicts with a bus request from another bus master, the "maximum wait time" of the bus master that requires real-time processing And the "scheduled time to occupy the shared bus" calculated from information transmitted by the bus master other than the bus master together with the bus request,
As a result, a bus master requiring real-time processing is pending, and if it is determined that the real-time processing is impaired, a means for preferentially giving a shared bus use right to the bus master requiring real-time processing is provided. Mediation system. 3. A shared bus, a plurality of bus masters that occupy the bus and perform data transfer, and a bus arbitration unit that arbitrates a bus request signal from the bus master and exclusively selects a bus master that gives a bus right. In the above system, each of the bus masters includes means for transmitting information that does not change among various information related to its own data transfer to the bus arbitration unit and registering the information in the bus arbitration unit. In the case where bus requests from a plurality of bus masters overlap, the bus arbitration unit transmits various information registered in the bus arbitration unit and data transmitted together with the bus request. Calculate the “scheduled time to occupy the shared bus” from the transfer information and compare it with the “maximum standby time” of the bus master that requires real-time processing. A bus arbitration system, comprising means for performing arbitration.