JPH10254823A - Bus arbitration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To flexibly cope with the case of equally giving a bus using right to any device and the case of giving priority in the acquiring of the bus using right to a specific device by avoiding the delay of a response to the bus using request by the successive inspection of the bus using request in a circulating priority order system. SOLUTION: Plural devices 102a to 102h are connected to one bus 101 to receive a bus using request signal 104 from the devices 102a to 102h. When a bus using request signal 104 is outputted from the plural devices 102a to 102h, a bus arbitration device 103 executing bus arbitration giving the bus using right permitting the access of the bus 101 stores a variable weighting value, which becomes different value at each device 102a to 102h executing a bus using request and varies the value each time of bus arbitration, to arbitrate this variable weighting value as the priority of the bus using right.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of assigning a priority by using a variable weighting value when a plurality of devices connected to one bus make a bus use request and a bus use right needs to be determined. The present invention relates to a bus arbitration device that determines and executes bus arbitration.

[0002]

2. Description of the Related Art Generally, in data transfer of a computer system, a plurality of devices are connected to one bus, and when the device uses the bus, the device becomes a bus master and starts data transfer. At this time, a plurality of devices simultaneously become bus masters, and data collision occurs on the bus that performs data transfer. Therefore, the number of bus masters is limited to only one.

[0003] In many systems, however, devices are required to request their own use of the bus.
Therefore, in consideration of a case where a plurality of devices request the use of the bus at the same time, the device outputs a bus use request signal for making a bus use request to the bus arbitration device, and One of the devices is selected, the selected device is used as a bus master, and the bus is permitted to be used.

At this time, as a method for selecting a device, a priority is fixedly determined for each device, and a first method for selecting a device having a higher priority or a method for selecting each device equally. There are the following two methods, which are performed without setting the priority.

[0005] The second method is a method for determining a bus master according to the cyclic priority method shown in FIG.
For example, when there are four devices connected to the bus, the bus use request signal output from the specified device in each state is checked cyclically, and it is confirmed that the signal is output. At that time, the right to use the bus is granted, the state is stagnated, and the state transitions at the next arbitration.
This is to check a bus use request of another device.

Further, when the priority is fixedly determined, if a high-priority device frequently uses the bus, another device may not have a chance to acquire the right to use the bus. .

On the other hand, in the above-mentioned cyclic priority system in which the priority is determined by circulating and checking the bus use request signal, in many cases, these signals are sequentially examined in synchronization with a clock. Therefore, after a certain device outputs a bus use request signal, it waits for several clocks until the bus arbitration device checks the signal of the device and responds. Therefore, for example, even when only one device requests the right to use the bus and arbitration is unnecessary, it is impossible to immediately respond.

Therefore, as a conventional technique for solving the above problem, for example, a "bus arbitration apparatus" disclosed in Japanese Patent Application Laid-Open No. Hei 7-134689 is disclosed. Here, the bus use requesting device outputs a value indicating a priority determined in advance by software to the bus arbitration device at the time of the bus use request. The bus arbitrator refers to these values, determines a device with a higher priority, and gives the right to use the bus. If there is a case where the values representing the priorities are the same between the devices, arbitration is performed only between those devices by the cyclic priority method.

[0009]

However, in the prior art as described above, a signal line for outputting a value indicating the priority to the bus arbitration device is required, In some cases, a device to which the bus right is granted is selected depending on the system, so that there is a problem that it is not possible to immediately respond to a bus use request.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and it is possible to avoid a delay in response to a bus use request due to sequential inspection of bus use requests in a cyclic priority system, and furthermore, to make any device equally. An object of the present invention is to flexibly cope with a case where a bus use right is given or a case where a superior advantage in acquiring a bus use right is given to a specific device.

[0011]

According to a first aspect of the present invention, there is provided a bus arbitration apparatus in which a plurality of devices are connected to one bus, and a bus use request from the devices is transmitted. A bus arbitration device for executing bus arbitration that grants a bus use right to permit access to the bus when the bus arbitration device receives the bus use request from the plurality of devices and conflicts with each other. A variable weighting value, which is different for each device that issues a use request and changes each time the bus is arbitrated, is stored, and the variable weighting is arbitrated as the priority of the bus use right.

That is, by determining priorities for determining the right to use the bus, the value of which changes each time bus arbitration is executed, the right to use the bus can be assigned to a plurality of devices connected to one bus. Equal opportunities are obtained, and a quick bus master (access right) is determined in response to a bus use request.

According to a second aspect of the present invention, in the bus arbitration apparatus, a plurality of devices are connected to one bus, a bus use request from the device is received, and the bus use request is output from the plurality of devices. And conflict,
In a bus arbitration device that performs arbitration that grants a bus use right that permits access to the bus, the bus arbitration device has a different value for each device that issues the bus use request, and the value changes each time the bus arbitration is performed. A variable weight value is stored, and a fixed weight value that is different for each device that makes the bus use request and does not change due to the bus arbitration is stored, and a variable weight value and the fixed weight value are stored. The sum is arbitrated as the priority of the right to use the bus.

That is, in addition to the variable weight value of the above-mentioned claim 1, by giving a fixed weight value whose value does not change due to bus arbitration, an invariant priority is provided for a specific device.

According to a third aspect of the present invention, in the bus arbitration apparatus, a plurality of devices are connected to one bus, a bus use request from the device is received, and the bus use request is output from the plurality of devices. And conflict,
In a bus arbitration device that performs arbitration that grants a bus use right that permits access to the bus, the bus arbitration device has a different value for each device that issues the bus use request, and the value changes each time the bus arbitration is performed. A variable weight value is stored, the devices are grouped according to priority, and priorities are determined and arbitrated prior to the priority based on the variable weight values.

That is, in addition to the variable weight value of the first aspect, a priority is given to each group, so that the priority of a device belonging to a specific group is increased.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a bus arbitration device of the present invention will be described in detail with reference to the accompanying drawings.

[Embodiment 1] In this embodiment 1,
A description will be given of an example in which a variable weighting value that differs for each device that issues a bus use request and changes each time bus arbitration is stored, and the previous variable weighting value is used as the priority for determining the bus use right.

FIG. 1 is a block diagram showing an example of a system configuration in which a plurality of devices are connected to one bus. In the figure, reference numeral 101 denotes a bus, and 102 denotes a plurality of (here, eight) devices 102a to 1 connected to the bus 101.
02h and 103 are bus arbitration devices that execute a bus arbitration operation described later.

Further, a bus use request signal 104 and a bus use permission signal 105 are individually connected to the bus arbitration device 103 from each of the devices 102a to 102h. Here, the bus use request signal 104 and the bus use permission signal 105 are not required for all the devices 102a to 102h connected to the bus 101, but need only be connected to the device for starting the bus use.

In the above configuration, the bus arbitration device 103
Outputs a bus use permission signal 105 to the device that has output the bus use request signal 104 to permit the start of data transfer. At this time, the plurality of devices 102a to 102h
Outputs the bus use request signal 104, the bus arbitration device 103 selects only one device based on the following priority, and outputs the bus use permission signal 105 only to the selected device.

In selecting a device, the bus arbitration device 1
03, when the bus use request signal 104 is output from a plurality of devices, in the first embodiment, each device 1
Weights corresponding to 02a to 102h are assigned, and the larger the value, the higher the priority.

Here, the weighting value is determined for each device 102a.
If the values are the same between -102h and 102h, the priority cannot be determined, so different values are taken. FIG. 2 shows examples of the weights and the priorities. Here are eight devices 1
It is assumed that 02a to 102h output the bus use request signal 104. As a weight value, for example, 0 to 7
Are assigned to each of the devices 102a to 102h. The priority is the same as the weight value.

In the column of bus use request, 1 is set when there is a bus use request, and 0 otherwise. The priority is compared only for the device whose value is 1 in the bus use request column, the device having the largest value is selected, and the bus use permission signal 105 is set to 1. In this example, the device 102d is selected. In this way, by determining the value of the priority, the bus master is immediately determined in response to the bus use request.

Here, the bus arbitration is performed by each of the devices 102a to 102a.
The weighting value is updated every time bus arbitration is performed in order to achieve equality between 102h. As shown in FIG. 3, for example, the update values of the weighting values are distributed so that the weight of the device selected in the previous arbitration is minimized, and the priority at the next arbitration is the lowest.

[Embodiment 2] In this embodiment 2,
Further, when it is desired to give a priority to a specific device, a unique and fixed weight value (where the former is a variable weight value, and the latter is a variable weight value) separately from the variable device weight value in the first embodiment. An example will be described in which a fixed weight is given) and the sum of the variable weight and the fixed weight is used as the priority for determining the bus use right.

That is, here, a different value is set for each device that makes a bus use request, and a variable weight value that changes every time the bus is arbitrated is stored, and becomes different for each device that makes a bus use request. The fixed weighting value whose value does not change is stored, and the sum of the variable weighting value and the fixed weighting value is used as the priority for determining the bus use right.

The priority required for determining the bus master is the sum of the variable weight value and the fixed weight value. At this time, the priority of the sum of the weighting values cannot be determined if the same value occurs. For example, as shown in FIG. 4, when the number of the specific devices giving fixed priority is limited to two, , 3n + 1 and 3n + 2 (n = 0, 1,...). The variable weight value is 3n (n =
0, 1,...) To avoid duplication of weight values.

At this time, if the value of n is increased, the effect of the priority increases. Conversely, if n is a negative value, the priority can be lowered. In the example shown in FIG.
Device 102c, device 102e, device 102
h outputs a bus use request, indicating that the device 102e is selected as a bus master only from the variable weight value, but the device 102c is selected as the bus master by the fixed weight value.

[Embodiment 3] In this embodiment 3,
A variable weighting value that varies for each device that makes a bus use request and changes at each bus arbitration is stored, and devices are grouped according to priority, and priority is determined by the variable weighting value. A description will be given of an example in which priorities are determined based on the above-described grouping and priorities are determined for determining the bus use right.

Here, in the third embodiment, some devices are grouped, and a fixed priority is given to the group as a priority level. The grouping by priority is performed, for example, as shown in FIG.
Into three groups. The higher the priority level, the higher the priority.

The priority required for the determination of the bus master is, for example, the sum of the value of the priority level * 8 and the variable weighting value as shown in FIG. In this way, the priority values do not overlap among the devices 102a to 102h, and the priority level by grouping has the highest priority.

[0033]

As described above, according to the bus arbitration apparatus according to the present invention (claim 1), the priority for determining the bus use right whose value changes each time bus arbitration is performed is determined. Therefore, the opportunity to acquire the right to use the bus can be equalized for a plurality of devices connected to one bus, and the bus master (access right) can be quickly determined in response to the bus use request.

According to the bus arbitration device of the present invention (claim 2), in addition to the variable weight value of claim 1,
By giving a fixed weight value whose value does not change due to bus arbitration, an invariant priority is set for a specific device, so that the superiority in acquiring the bus use right can be flexibly given to a specific device. .

According to the bus arbitration device of the present invention (claim 3), in addition to the variable weight value of claim 1,
By giving a priority to each group, the priority for devices belonging to a specific group is raised, so that the superiority in acquiring the right to use the bus can be flexibly given to a specific device.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a system configuration example in which a plurality of devices are connected to one bus.

FIG. 2 is a table showing fixed weight values and priorities of devices according to the first embodiment;

FIG. 3 is a table showing weighted update values according to the first embodiment;

FIG. 4 is a table showing fixed weight values, variable weight values, and priorities of devices according to the second embodiment;

FIG. 5 is a table showing priority levels, variable weight values, and priorities of devices according to the third embodiment;

FIG. 6 is an explanatory diagram illustrating an example of determining a bus master according to a cyclic priority scheme.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Bus 102a-102h Device 103 Bus arbitration device 104 Bus use request signal 105 Bus use permission signal

Claims (3)

[Claims] 1. A plurality of devices are connected to one bus,
A bus arbitration device that receives a bus use request from the device and executes a bus arbitration that grants a bus use right that permits access to the bus when the bus use requests are output from the plurality of devices and there is a conflict. The bus arbitration device stores a variable weighting value that differs for each device that makes the bus use request, and changes the value each time the bus arbitration is performed, and stores the variable weighting value as a priority of the bus use right. A bus arbitration device that arbitrates as a bus. 2. A plurality of devices are connected to one bus,
A bus arbitration device that receives a bus use request from the device and executes arbitration that grants a bus use right to permit access to the bus when the bus use requests are output from the plurality of devices and there is a conflict; The bus arbitration device stores a variable weighting value that changes for each device that makes the bus use request, and a variable weighting value that changes every time the bus arbitration is performed. A bus arbitration device which stores a fixed weight value whose value does not change due to bus arbitration, and arbitrates a sum of the variable weight value and the fixed weight value as a priority of a bus use right. 3. A plurality of devices are connected to one bus,
A bus arbitration device that receives a bus use request from the device and executes arbitration that grants a bus use right to permit access to the bus when the bus use requests are output from the plurality of devices and there is a conflict; The bus arbitration device stores a variable weighting value that varies for each device that makes the bus use request, and changes the value each time the bus arbitration is performed. A bus arbitration device, wherein priorities based on weighting values are determined prior to said grouping priorities and arbitration is performed.