JP2000250852A - Bus arbitrating device, bus system and bus arbitrating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce average start rating or average access time. SOLUTION: A bus system 1 is provided with a bus 10, a bus arbitrating device 20 and bus agents 31-36. Before a transaction using a bus 10, the respective bus agents 31-33 transmit a bus usage request signal, access object bus agent information, a transaction kind and a data transfer amount to the bus arbitrating device 20. While referring to a transfer performance table, the bus arbitrating device 20 performs bus arbitration. While defining any one of bus agents 31-36 as a master and defining the other agents as slaves, this transfer performance table stores data transfer performance characteristic values for each kind of transaction between these master and slaves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bus arbitration device, a bus system, and a bus arbitration method used in an information processing system such as a computer and a peripheral device.

[0002]

2. Description of the Related Art In an information processing system, a connection mode between devices (computers and peripheral devices, etc.) for transmitting and receiving data is less expensive than a one-to-one connection system in which an independent signal line is prepared for each data path. In many cases, a common bus connection method that can be configured as follows is used. In this common bus connection method, a device connected to a common bus or a functional module that performs bus access inside the device is called a bus agent. The bus system based on the common bus connection system includes a bus arbitration device in addition to the bus and the bus agent. A bus agent that intends to use the bus requests a bus arbitration device from the bus arbiter. When a plurality of bus agents output a bus use right request, the bus arbitrating device selects one of the bus use requests and gives the bus use right to the one bus agent. The bus agent granted the right to use the bus uses the bus to perform a data transfer transaction with another bus agent.

Here, the bus agent that has requested the bus use right is called a master. The bus agent to be accessed by the master for performing a transaction is called a slave. The time required from the request of the bus use right by the master to the start of the transaction after the acquisition of the bus use right is called start latency. The time required from the request for the right to use the bus by the master to the end of the transaction is called access time. The amount of data transferred per unit time via the bus during the execution of a transaction is called a transfer rate.
As an index indicating the performance of the bus system, an average value of each of the start latency, the access time, and the transfer rate is used. That is, the smaller the average start latency and the average access time, the better, and the larger the average transfer rate, the better. In order to optimize these values, various bus control methods are employed.

For example, when the first bus agent has a low-speed and large-capacity storage means, the first bus agent includes a small-capacity read buffer and a small-capacity write buffer that can be accessed at high speed. And
When the first bus agent receives a data read request from another second bus agent, the first bus agent predicts that there will be a data read request again from the second bus agent shortly thereafter. Is read from the storage means and stored in the read buffer in advance.
This is called prefetch. When data is written from another second bus agent, the first bus agent temporarily writes the data to the write buffer, then reads the data once written to the write buffer to store the data at a low speed. Write to the means. This is called Posted Light. By doing so, the bus use time during the transaction between the first bus agent and the second bus agent is reduced, and the performance of the bus system is improved.

[0005] The performance of the bus system has also been improved by improving the bus arbitration method. For example, JP-A-9
In the bus system disclosed in JP-A-185580,
When requesting the bus arbitration device for the bus arbitration device, the bus agent that intends to use the bus, that is, the master, also notifies the bus arbitration device of the expected data transfer amount. When a plurality of masters output a bus use right request, the bus arbitration device determines the time for each master to use the bus based on the data transfer amount expected by each master and the data transfer performance characteristic value of each master. Predict, select one master based on the prediction result, and give the one master the right to use the bus. By arbitrating the right to use the bus in this way, the average start latency and the average access time are reduced to improve the performance of the bus system. Further, in the bus system disclosed in the above publication, the bus agent executes various transactions, obtains the data transfer performance characteristic value based on the result of the executed transaction, stores the data transfer performance characteristic value in a table, and stores the data transfer performance characteristic value in the table. Arbitration is performed based on the stored data transfer performance characteristic values.

[0006]

In the bus system disclosed in the above publication, the data transfer performance characteristic value stored in the table depends only on each master. However, since the data transfer performance during a transaction generally depends on the combination of the master and the slave, the average start latency and the average access time are not necessarily set depending on the bus agent to be accessed by each master, that is, the slave. In some cases, the size cannot be reduced, and the performance of the bus system cannot be sufficiently improved.

In the bus system disclosed in the above publication, the data transfer performance characteristic value stored in the table is:
It is obtained based on the result of the transaction executed to obtain the value. However, the data transfer performance characteristic value obtained in this manner does not reflect the back-end operation (prefetch or posted write) that occurs in the bus agent at the time of the transaction in the actual bus system operation, and It may be a value far from the characteristic value at the time of the transaction. Therefore, also in this regard, the average start latency and the average access time cannot always be reduced, and the performance of the bus system may not be sufficiently improved.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a bus arbitration apparatus, a bus system, and a bus arbitration method that can reduce the average start latency and the average access time. And

[0009]

A first bus arbitration device according to the present invention is a bus arbitration device that arbitrates a bus use right request of each of a plurality of bus agents connected to a bus, and (1) A transfer performance table that stores data transfer performance characteristic values for each transaction type between these masters and slaves, with one of the plurality of bus agents as a master and the other as a slave, and (2) a plurality of bus agents. Input means for inputting a bus use right request signal output by any one of the bus agents as a master, information on a bus agent to be accessed, a transaction type, and a data transfer amount; (3) any one of the plurality of bus agents If two or more devices become the masters and the bus usage right request signal is output and the bus usage right requests conflict, each master and each master A bus use that grants a bus use right to any master by referring to the transfer performance table based on the slave indicated by the input access target bus agent information, the transaction type and the data transfer amount output from each master. Right grant means.

In the first bus arbitration device, any two or more of a plurality of bus agents connected to the bus become masters, output a bus usage right request signal, and the bus usage right requests compete. , The right to use the bus is granted to any one of the masters. In order to perform this arbitration, the bus arbitration device uses any one of the plurality of bus agents as a master and any other as a slave to determine a data transfer performance characteristic value for each transaction type between the master and the slave. It has a transfer performance table to store. Further, the bus arbitration device inputs a bus use right request signal, access target bus agent information, a transaction type, and a data transfer amount output by any one of the plurality of bus agents acting as a master. Then, the bus arbitration device refers to the transfer performance table based on each master, the slave indicated by the access target bus agent information output from each master, the transaction type and the data transfer amount output from each master, The right to use the bus is given to one of the masters. In this way, the bus arbitration device identifies not only the master but also the slave, predicts the time required for the transaction, and performs the bus arbitration based on the prediction result, thereby reducing the average start latency and the average access time. Thus, the performance of the bus system is improved.

In the first bus arbitration device, the transfer performance table may use any one of the plurality of bus agents as a master and optionally specify a data transfer performance characteristic value for each transaction type without specifying a slave. It is also preferable to store the information. In this case, even if the master bus agent cannot notify the bus control device of the bus agent information to be accessed, the bus arbitration device must specify the slave by referring to the transfer performance table. And the time required for the transaction can be predicted.

A second bus arbitration device according to the present invention is a bus arbitration device for arbitrating a bus use right request of each of a plurality of bus agents connected to a bus. A data transfer performance characteristic value for each transaction type between a specific master and an arbitrary slave is stored, and data transfer for each transaction type between a specific slave and an arbitrary master among a plurality of bus agents is stored. A transfer performance table storing performance characteristic values, and (2) a bus use right request signal output by any one of the plurality of bus agents as a master, access target bus agent information, a transaction type, and a data transfer amount. Input means for inputting, and (3) at least two of the plurality of bus agents become masters and require bus usage rights. When a signal is output and the bus use right request is in conflict, each master, the slave indicated by the access target bus agent information output from each master, the transaction type output from each master, and the data transfer amount are used. And a bus use granting means for granting a bus use right to any master by referring to the transfer performance table.

In the second bus arbitration device, any two or more of the plurality of bus agents connected to the bus become masters, output a bus usage right request signal, and compete for bus usage right requests. , The right to use the bus is granted to any one of the masters. In order to perform this arbitration, the bus arbitration device stores the data transfer performance characteristic value for each transaction type between a specific master and any slave among the plurality of bus agents, and Has a transfer performance table for storing data transfer performance characteristic values for each transaction type between a specific slave and an arbitrary master. Further, the bus arbitration device inputs a bus use right request signal, access target bus agent information, a transaction type, and a data transfer amount output by any one of the plurality of bus agents acting as a master. Then, the bus arbitration device, based on each master, the slave indicated by the access target bus agent information output from each master, the transaction type and the data transfer amount output from each master, , Referring to both the data transfer performance characteristic value stored for the specific master and the data transfer performance characteristic value stored for the specific slave, and determining the time required for the transaction based on both values. Predict. The bus arbitration device performs arbitration based on the time thus predicted. In this way, the bus arbitration device identifies not only the master but also the slave, predicts the time required for the transaction, and performs the bus arbitration based on the prediction result, thereby reducing the average start latency and the average access time. Thus, the performance of the bus system is improved. Further, the size of the transfer performance table stored in the bus arbitration device can be reduced.

[0014] Each of the first and second bus arbitration devices, based on the result of the executed transaction,
Preferably, the apparatus further comprises a table updating means for updating the data transfer performance characteristic value stored in the transfer performance table. In this case, a high-precision data transfer performance characteristic value that reflects a back-end operation (prefetch or posted write) that occurs in the bus agent at the time of a transaction during an actual bus system operation is obtained. Thus, even when the transfer performance dynamically changes, a highly accurate data transfer performance characteristic value can be obtained. As a result, the average start latency and the average access time are further reduced, and the performance of the bus system is improved.

Each of the first and second bus arbitration devices selects a master and a slave from a plurality of bus agents, executes a transaction between the master and the slave, and executes the executed transaction. Preferably, the apparatus further comprises table initialization means for storing the data transfer performance characteristic value in the transfer performance table based on the result of (1). In this case,
A data transfer performance characteristic value can be obtained even for a bus agent that cannot notify the bus arbiter of the required time of a transaction, and the data transfer performance characteristic value can be obtained before the bus system starts an actual operation. As a result, the average start latency and the average access time are reduced, and the performance of the bus system is improved.

The bus system according to the present invention has the following features. (1) When the bus system is connected to a bus and requests a bus use right as a master,
A plurality of bus agents that output a bus usage right request signal, information on a bus agent to be accessed, a transaction type, and a data transfer amount; and (2) a bus usage right output by one of the plurality of bus agents serving as a master. A bus arbitration device that grants a bus use right to any master when a bus use right request is in conflict, based on the request signal, the access target bus agent information, the transaction type, and the data transfer amount; It is characterized by having. This bus system includes the first or second bus arbitration device. The average start latency and the average access time are reduced, and the performance is improved.

The bus arbitration method according to the present invention is based on the same technical concept as the above-described bus arbitration device according to the present invention. According to this bus arbitration method, the average start latency and the average access time are reduced, and the performance of the bus system is improved.

[0018]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First Embodiment First, a first embodiment of a bus system, a bus arbitration device, and a bus arbitration method according to the present invention will be described.

FIG. 1 is a configuration diagram of a bus system 1 according to the first embodiment. This bus system 1 includes a bus 1
0, a bus arbitration device 20, and bus agents 31 to 36 connected to the bus 10.
Here, the number of bus agents connected to the bus 10 is six, but the number is not limited to six.
It is also assumed that among these six bus agents, each of the bus agents 31 to 33 can be a master and a slave.
It is assumed that each of 4 to 36 can be a slave.

Bus agents 31 to 31 which can be masters
33 are connected to the bus arbitration device 20 via a bus use right request signal line and a bus use right permission notification line. That is, the bus agent 31 is connected to the bus arbitration device 20 via the bus use right request signal line 41 and the bus use right permission notification line 51. The bus agent 32 is connected to the bus arbitration device 20 via a bus usage right request signal line 42 and a bus usage right permission notification line 52. Further, the bus agent 33 is connected to the bus arbitration device 20 via a bus use right request signal line 43 and a bus use right permission notification line 53.

Each of the bus agents 31 to 33
When the bus 10 is used as a master to access another bus agent to execute a transaction, prior to this transaction, the bus 10
A bus use right request signal indicating that a use right is requested, access target bus agent information indicating another bus agent to be accessed, a write or read transaction to be executed, and a type of the transaction to be executed. The expected data transfer amount is transmitted to the bus arbitration device 20 via the bus usage right request signal lines 41 to 43.

The bus arbitration device 20 includes a bus agent 3
When a bus use right request signal is output from any of 1 to 33, it is input and arbitrated according to a predetermined arbitration algorithm. At this time, the bus arbitration device 20 performs arbitration with reference to the transfer performance table. Then, the bus arbitration device 20 gives the bus use right to any one of the bus agents selected by the arbitration, and notifies the bus agent via the bus use right permission notification line. Then, the bus agent, which has received the notification of the permission to use the bus, waits until the bus 10 becomes available, and starts the permitted transaction.

Although the bus use right request signal line 41 and the bus use right permission notification line 51 are different signal lines from each other in FIG. 1, they may be common signal lines.
It may be partially common to the bus 10. A bus use right request signal line 42 and a bus use right permission notification line 52;
The same applies to the bus use right request signal line 43 and the bus use right permission notification line 53.

FIG. 2 is a chart for explaining a transfer performance table in the bus arbitration device 20 according to the first embodiment. The bus arbitration device 20 has a storage unit for storing a transfer performance table. This transfer performance table stores data transfer performance characteristic values for each transaction type between the master and the slave, with any one of the bus agents 31 to 36 as a master and the other as a slave. .

In the transfer performance table shown in FIG. 2, the bus agent 31 is used as a master and the bus agent 32
To 34 as slaves, when the bus agent 32 is the master and the bus agents 31 and 34 are the slaves, and when the bus agent 33 is the master and the bus agents 31 and 34
If each is a slave, for each write or read transaction type,
The required number of bus cycles is stored as a transfer performance characteristic value for each value (1, 4 and 8) of the data transfer amount that can be transferred per transaction.

For example, when a write transaction with a data transfer amount of 8 is performed using the bus agent 31 as a master and the bus agent 32 as a slave, the number of bus cycles required for the transaction is 19. When a read transaction is performed with a data transfer amount of 8 using the bus agent 32 as a master and the bus agent 34 as a slave, the number of bus cycles required for the transaction is 29. Also, when a write transaction with a data transfer amount of 8 is performed using the bus agent 33 as a master and the bus agent 34 as a slave, the number of bus cycles required for the transaction is 25.

The transfer performance table shown in FIG.
For example, the transfer performance characteristic values when the bus agent 32 is the master and the bus agent 33 is the slave are not shown. This is because it is not necessary to store the transfer performance characteristic value if it is known that a transaction in such a case will not be performed.

Next, the operation of the bus system 1 and the bus arbitration device 20 according to the present embodiment will be described, and the bus arbitration method according to the present embodiment will be described. Here, a write transaction T1 with a data transfer amount of 8 using the bus agent 31 as a master and the bus agent 32 as a slave, and a data transfer amount of 8 using the bus agent 32 as a master and the bus agent 34 as a slave.
And a write transaction T with a data transfer amount of 8 using the bus agent 33 as a master and the bus agent 34 as a slave.
Suppose that three bus use requests 3 occur simultaneously in bus cycle 1. As the arbitration algorithm, an arbitration algorithm that performs arbitration so that the average start latency is minimized is employed.

Under this arbitration algorithm, the bus arbitration device 20 refers to the transfer performance table and arbitrates such that transactions are performed in order from the one whose execution time is predicted to be short. That is, the bus arbitration device 20 transmits the bus agent 3 among the transactions T1 to T3.
When a write transaction T1 with a data transfer amount of 8 is performed with 1 as the master and the bus agent 32 as the slave, the number of bus cycles required is 19, which is the shortest. Therefore, a bus use right is requested to perform the transaction T1. The right to use the bus is given to the bus agent 31 that has made it. Then, the bus agent 31 executes a transaction using the bus 10 during the bus cycles 2 to 20.

Subsequently, the bus arbitrating device 20 selects the bus agent 3 among the remaining transactions T2 and T3.
Since the number of bus cycles required for performing a write transaction T3 with a data transfer amount of 8 using the master 3 as a slave and the bus agent 34 as a slave is 25, which is the shortest, a bus use right is requested to perform the transaction T3. The right to use the bus is given to the bus agent 33 that has made it. The bus agent 33 executes a transaction using the bus 10 during the bus cycles 21 to 45.

Finally, the bus arbitrating device 20 gives the bus use right to the bus agent 32 which has requested the bus use right to execute the transaction T2. And
Bus agent 32 executes a transaction using bus 10 during bus cycles 46-74.

By performing the arbitration in this manner, the start latency of each transaction is 1,20 in the order of execution.
And 45, giving an average start latency of 22.

For comparison, FIG. 3 shows a table for explaining a transfer performance table in the bus arbitration apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 9-185580, which is described in the section of the prior art.
This conventional transfer performance table does not store information on slaves. Therefore, when the bus agent 31 is the master, the transfer performance characteristic value when the bus agent 32 is the slave is adopted. When the bus agent 32 is the master, the transfer performance characteristic value when the bus agent 31 is the slave is adopted. Also,
When the bus agent 33 is the master, the transfer performance characteristic value when the bus agent 31 is the slave is adopted.

In the case of this comparative example, according to the transfer performance table, the transaction T
The required number of bus cycles of 1 is 19, the required number of bus cycles of the transaction T2 by the bus agent 32 is 15, and the required number of bus cycles of the transaction T3 by the bus agent 33 is 16. Therefore, according to an arbitration algorithm that performs arbitration so that the average start latency is minimized, the bus agent 32, the bus agent 33, and the bus agent 31 are given the right to use the bus in this order.

As a result, in the comparative example, first, the bus agent 32 performs the transaction T2 in which the actual number of required bus cycles is 29 in the period of the bus cycles 2 to 30. Subsequently, the bus agent 33 executes the transaction T3 in which the actual required bus cycle number is 25.
Is performed during the bus cycles 31 to 55. Finally, the bus agent 31 determines that the actual number of required bus cycles is one.
The transaction T1 which is 9
Performed during period 74. By performing the arbitration in this manner, the start latencies of the transactions are 1, 30, and 55 in the order of execution, and the average start latencies are about 2
7.7.

As described above, in the bus system, the bus arbitration device, and the bus arbitration method according to the present embodiment, the average start latency is shortened and the performance of the bus system 1 is improved as compared with the comparative example. In the above description, the arbitration algorithm that performs arbitration so as to minimize the average start latency is adopted. However, the same effect can be obtained even when the arbitration algorithm that performs arbitration so as to minimize the average access time is employed.

In this embodiment, the data transfer performance characteristic value stored in the transfer performance table of the bus arbitration device 20 is preferably updated based on the result of the actually executed transaction. Specifically, for example,
When each of the transactions T1 to T3 described above is performed, the bus arbitration device 20 obtains the number of bus cycles actually required by each transaction, and updates and stores the obtained number of bus cycles in the transfer performance table. .
By doing so, a highly accurate data transfer performance characteristic value reflecting a back-end operation (prefetch or posted write) occurring in the bus agent at the time of a transaction during an actual bus system operation can be obtained. Even when the transfer performance of the bus agent fluctuates dynamically, a highly accurate data transfer performance characteristic value can be obtained. As a result, the average start latency and the average access time can be further reduced, and the performance of the bus system 1 can be sufficiently improved.

In the present embodiment, a master and a slave are selected from the bus agents 31 to 36, a transaction is executed between the master and the slave, and a transaction is executed based on a result of the executed transaction. It is also preferable to store the data transfer performance characteristic value in the transfer performance table of the bus arbitration device 20 as an initial value. Specifically, for example, immediately after the power supply to the bus system 1 is started, the bus arbitrating device 20 instructs the bus agent 31 to perform a transaction using the bus agent 32 as a master and the bus agent 32 as a slave. Then, when this transaction is performed, the bus arbitration device 20 measures the number of bus cycles actually required by the transaction, and stores the measured number of bus cycles in the transfer performance table. By doing so, a data transfer performance characteristic value can be obtained even for a bus agent that cannot notify the bus arbitration device 20 of the time required for a transaction. The transfer performance characteristic value is obtained. As a result, the average start latency and the average access time can be reduced, and the performance of the bus system 1 can be sufficiently improved.

(Second Embodiment) Next, a second embodiment of the bus system, the bus arbitration device and the bus arbitration method according to the present invention will be described. The configuration of the bus system according to the present embodiment is the same as that shown in FIG.

FIG. 4 is a chart for explaining a transfer performance table in the bus arbitration device according to the second embodiment. The transfer performance table included in the bus arbitration device 20 according to the present embodiment is configured such that any one of the bus agents 31 to 36 is set as a master and any one of the bus agents 31 to 36 is specified without specifying a slave.
It stores data transfer performance characteristic values for each transaction type. That is, as shown in FIG. 4, the transfer performance table shows that the data transfer performance characteristics for each transaction type (write / read) can be obtained even when the bus agents 31 to 33 are used as masters and the slaves are specified without specifying the slaves. Store the value.

The bus arbitration method according to this embodiment is substantially the same as in the first embodiment. However, in the present embodiment, when each of the bus agents 31 to 33 that can be masters transmits the bus usage right request signal to the bus arbitration device 20, the bus agents 31 to 33 also transmit the transaction information and the data transfer amount together. In some cases, the access target bus agent information indicating another target bus agent is not transmitted. For example, assume that a bus agent 31 that intends to perform a write transaction sends a bus use right request signal without accompanying access target bus agent information. At this time, the bus arbitrating device 20 sets the data transfer performance characteristic value 20 in the case where the bus agent 31 is specified as the master and the slave is specified without specifying the slave in the storage contents of the transfer performance table.
It is estimated that the number of bus cycles is necessary for performing the transaction. Then, the bus arbitration device 20 performs arbitration based on the number of bus cycles predicted in this way.

The bus system, the bus arbitration device, and the bus arbitration method according to the present embodiment have the following effects in addition to the same effects as those of the first embodiment. That is, in the present embodiment, even when the master bus agent cannot notify the bus control device 20 of the bus agent information to be accessed, the average start latency and the average access time can be reduced, The performance of the system 1 can be sufficiently improved.

As in the case of the first embodiment, in this embodiment, the data transfer performance characteristic value stored in the transfer performance table of the bus arbitration device 20 is based on the result of the actually executed transaction. Preferably, it is updated. Also in the present embodiment, the bus agent 31
36, a master and a slave are selected, a transaction is executed between the master and the slave, and the data transfer performance is stored in the transfer performance table of the bus arbitration device 20 based on the result of the executed transaction. It is also preferable to store the characteristic values as initial values.

(Third Embodiment) Next, a third embodiment of the bus system, the bus arbitration device and the bus arbitration method according to the present invention will be described. The configuration of the bus system according to the present embodiment is the same as that shown in FIG.

FIG. 5 is a chart for explaining a transfer performance table in the bus arbitration device according to the third embodiment. The transfer performance table of the bus arbitration device 20 according to the present embodiment stores data transfer performance characteristic values for each transaction type between a specific master and any slave among the bus agents 31 to 36, and It stores a data transfer performance characteristic value for each transaction type between a specific slave among the agents 31 to 36 and an arbitrary master.

The bus arbitration method according to this embodiment is substantially the same as in the first embodiment. Also in the present embodiment, each of the bus agents 31 to 33 that can be the master
When transmitting the bus use right request signal to the bus arbitration device 20, the bus arbitration device 20 also transmits the access target bus agent information, the transaction information, and the data transfer amount.
However, in the present embodiment, the bus arbitration device 20 includes, in the storage contents of the transfer performance table, a data transfer performance characteristic value when the slave is specified without specifying the slave for the specific master, and the specific slave Arbitration is performed by referring to both the data transfer performance characteristic values when the master is determined without specifying the master.

Specifically, for example, the bus agent 31
It is assumed that there is a bus use right request for a write transaction T1 having a data transfer amount of 8 with the master as the master and the bus agent 32 as the slave. At this time, the bus arbitration device 20
Is a data transfer performance characteristic value 20 when the master is a bus agent 31 without specifying a slave, and a storage content is arbitrary without specifying a master as a bus agent 32. With reference to both of the data transfer performance characteristic values 19 in the case of, the larger value (or the average value) of both is predicted to be the number of bus cycles necessary for performing the transaction T1. And the bus arbitration device 2
0 performs arbitration based on the number of bus cycles predicted in this way.

The bus system, the bus arbitration device, and the bus arbitration method according to the present embodiment have the following effects in addition to the same effects as those of the first embodiment. That is, in the present embodiment, the bus arbitration device 20
Can reduce the size of the transfer performance table stored by the.

Also, as in the first embodiment, in the present embodiment, the data transfer performance characteristic value stored in the transfer performance table of the bus arbitration device 20 is based on the result of the actually executed transaction. Preferably, it is updated. Also in the present embodiment, the bus agent 31
36, a master and a slave are selected, a transaction is executed between the master and the slave, and the data transfer performance is stored in the transfer performance table of the bus arbitration device 20 based on the result of the executed transaction. It is also preferable to store the characteristic values as initial values.

[0051]

As described above in detail, according to the present invention, not only the master but also the slave are specified, the time required for the transaction is predicted based on the transfer performance table, and the bus is estimated based on the prediction result. Mediation,
The average start latency and the average access time are reduced, and the performance of the bus system is improved.

When the transfer performance table stores any one of the plurality of bus agents as a master and optionally stores a data transfer performance characteristic value for each transaction type without specifying a slave, Even if the bus agent cannot notify the bus control device of the access target bus agent information, the bus arbitration device refers to the transfer performance table,
It is possible to predict the time required for a transaction without specifying a slave.

The transfer performance table stores a data transfer performance characteristic value for each transaction type between a specific master and an arbitrary slave among the plurality of bus agents, and specifies a specific one of the plurality of bus agents. When storing the data transfer performance characteristic value for each transaction type between a slave and an arbitrary master, not only the master but also the slave is specified, and the time required for the transaction is predicted, and based on the prediction result, Since the bus arbitration is performed, the average start latency and the average access time are reduced, and the performance of the bus system is improved. Further, the size of the transfer performance table can be reduced.

In the case where the data transfer performance characteristic value stored in the transfer performance table is updated based on the result of the executed transaction, the back-up generated in the bus agent at the time of the transaction during the actual bus system operation is performed. A highly accurate data transfer performance characteristic value that reflects the end operation (prefetch or posted write) is obtained, and even when the transfer performance of the bus agent fluctuates dynamically, the highly accurate data transfer performance characteristic is obtained. Value is obtained. As a result, the average start latency and the average access time are further reduced, and the performance of the bus system is improved.

A master and a slave are selected from a plurality of bus agents, a transaction is executed between the master and the slave, and a data is stored in a transfer performance table based on a result of the executed transaction. When the transfer performance characteristic value is stored, the data transfer performance characteristic value can be obtained even for the bus agent that cannot notify the bus arbitration device of the required time of the transaction, and before the bus system starts the actual operation. Then, the data transfer performance characteristic value is obtained. As a result, the average start latency and the average access time are reduced, and the performance of the bus system is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a bus system according to a first embodiment.

FIG. 2 is a diagram illustrating a transfer performance table in the bus arbitration device according to the first embodiment.

FIG. 3 is a diagram illustrating a transfer performance table in a conventional bus arbitration device.

FIG. 4 is a diagram illustrating a transfer performance table in a bus arbitration device according to a second embodiment.

FIG. 5 is a table illustrating a transfer performance table in a bus arbitration device according to a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bus system, 10 ... Bus, 20 ... Bus arbitration device,
31 to 36 bus agent, 41 to 43 bus use request signal lines, 51 to 53 bus use permission notification lines.

Claims (11)

[Claims] 1. A bus arbitration device for arbitrating a bus use right request of each of a plurality of bus agents connected to a bus, wherein one of the plurality of bus agents is a master and the other is a slave. A transfer performance table storing a data transfer performance characteristic value for each transaction type between the master and the slave, and a bus use right request signal output as one of the plurality of bus agents serving as a master. Input means for inputting information on a bus agent to be accessed, a transaction type, and a data transfer amount; a bus use right request signal is output when any two or more of the plurality of bus agents serve as a master to output a bus use right request signal Conflicts with each other, the access target bus agent information output from each master A bus use right granting means for granting a bus use right to any one of the masters by referring to the transfer performance table based on the instructed slave, the transaction type and the data transfer amount output from each master. A bus arbitration device characterized by the following. 2. The transfer performance table according to claim 1, wherein any one of the plurality of bus agents is used as a master and a data transfer performance characteristic value is stored for each transaction type without specifying a slave. The bus arbitration device according to claim 1, wherein 3. A bus arbitration device that arbitrates a bus use right request of each of a plurality of bus agents connected to a bus, the bus arbitration device comprising a bus master and an arbitrary slave among the plurality of bus agents. A transfer performance table storing a data transfer performance characteristic value for each transaction type, and storing a data transfer performance characteristic value for each transaction type between a specific slave and any master among the plurality of bus agents; An input unit for inputting a bus use right request signal, an access target bus agent information, a transaction type, and a data transfer amount output by any one of the plurality of bus agents as a master; Any two or more become masters and output a bus use request signal to use the bus. When the right requests conflict, each master, the slave indicated by the access target bus agent information output from each master, the transaction type and the data transfer amount output from each master, the transfer performance table is updated. A bus arbitration device for granting a bus usage right to any one of the masters. 4. The apparatus according to claim 1, further comprising table updating means for updating a data transfer performance characteristic value stored in the transfer performance table based on a result of the executed transaction. Bus arbitration device. 5. A master and a slave are selected from the plurality of bus agents, a transaction is executed between the master and the slave, and the transfer performance table is determined based on a result of the executed transaction. 4. The bus arbitrating device according to claim 1, further comprising a table initializing means for storing a data transfer performance characteristic value in the bus arbitration device. 6. A plurality of bus agents which are connected to a bus and output a bus use right request signal, access target bus agent information, transaction type and data transfer amount when requesting a bus use right as a master. A bus use right request competes based on a bus use right request signal output by any one of the plurality of bus agents as a master, access target bus agent information, transaction type, and data transfer amount. A bus system comprising: a bus arbitrating device according to claim 1, wherein a bus use right is granted to any master in such a case. 7. A bus arbitration method for arbitrating a bus use right request of each of a plurality of bus agents connected to a bus, wherein one of the plurality of bus agents is a master and the other is a slave. A transfer performance table for storing a data transfer performance characteristic value for each transaction type between the master and the slave, wherein any one of the plurality of bus agents becomes a master and outputs a bus use right request. A signal, an access target bus agent information, a transaction type, and a data transfer amount are input, and any two or more of the plurality of bus agents serve as a master, and a bus use right request signal is output. In case of conflict, each master and the access target bus agent information output from each master indicate A bus arbitration method comprising: granting a bus use right to any master by referring to the transfer performance table based on a transaction type and a data transfer amount output from a slave and each master. 8. The transfer performance table stores any one of the plurality of bus agents as a master and a data transfer performance characteristic value for each transaction type without specifying a slave. The bus arbitration method according to claim 7, wherein 9. A bus arbitration method for arbitrating a bus use right request of each of a plurality of bus agents connected to a bus, the bus arbitration method comprising the steps of: There is a transfer performance table for storing the data transfer performance characteristic value for each transaction type and for storing the data transfer performance characteristic value for each transaction type between a specific slave of the plurality of bus agents and an arbitrary master. A bus use right request signal, an access target bus agent information, a transaction type, and a data transfer amount which are output as any of the plurality of bus agents as a master; Or two or more become masters, output a bus request signal, and When there is contention, each master, the slave indicated by the access target bus agent information output from each master, the transaction type and the data transfer amount output from each master, refer to the transfer performance table. A bus arbitration method, wherein a bus use right is given to any one of the masters. 10. The bus arbitration method according to claim 7, wherein the data transfer performance characteristic value stored in the transfer performance table is updated based on a result of the executed transaction. 11. A master and a slave are selected from the plurality of bus agents, a transaction is executed between the master and the slave, and the transfer performance table is determined based on a result of the executed transaction. The bus arbitration method according to claim 7 or 9, wherein the data transfer performance characteristic value is stored in the bus.