JPH10307788A - Bus bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade overhead for useless retrial and to prevent the throughput of a bus from being reduced by outputting a retrial response to a current bus master only when a response from a slave is delayed. SOLUTION: The bus bridge 10 is constituted so as to connect a bus A connected to a bus master A11 to a bus B connected to a bus slave B21. The bridge 10 is provided with a response time monitoring means 101 for monitoring the time of a response from the slave B21, and if the means 101 detects the absence of an access completion response from the slave B21 within a fixed time at the time of accessing the slave B21 from the master A11 through the bridge 10, the bridge 10 transmits a retrial signal to the master A11 and opens the bus A. At the time of detecting the access completion response within the fixed time, the bridge 10 allows the master A11 to hold the bus A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Bus (Busb) connecting two buses (Bus)
Ridge). When a bus master accesses a bus slave via a bus bridge, it generally involves a change in the protocol of the bus, so that an access time is longer than when a slave on the same bus is accessed. Then, while one master is accessing the bus slave via the bus bridge, the other bus masters cannot use the bus, and the throughput of the entire bus decreases. There is a need for a technique for preventing this decrease in throughput.

[0002]

2. Description of the Related Art To avoid this problem, there has been a technique called "delayed transaction" as a conventional technique. This method uses the retry function of the bus.

For example, in FIG. 2, when the bus master A11 tries to access the bus slave B21 in FIG.
And the requested contents (target slave name,
Address, data attributes, etc.), and sends a retry response to the bus master A11. The bus master A11 that has received the retry response releases the bus A once,
After a certain time, the same access (bus slave B21)
Access) again.

During this time, the bus bridge is connected to the bus master A11.
Performs access to the bus B requested by the
Data transfer or reception is performed with respect to. The bus bridge does not accept the re-execution request of the bus master A11 until the access of the bus slave B21 is completed.

As described above, the bus master receiving the retry response once releases the bus, so that other bus masters (for example, the bus masters A12 and A13) can use the bus, and the throughput of the bus A cannot be reduced. Did not.

[0006]

In the above-mentioned conventional "delayed transaction" system, the bus bridge always sends a retry response to the requesting bus master. Therefore, when the bus master re-executes access, it must perform the same bus protocol as the first time. The protocol of this bus varies depending on the installed bus, but in general, the right to use the bus (bus master right) is acquired, the address is transmitted, and the attribute of data (read or write, amount of data, etc.) is transmitted. And data transmission (at the time of data transmission).

Therefore, the re-execution of the bus is accompanied by the overhead (オ ー バ). If it is assumed that one master is accessing the bus while another master does not use the bus, the overhead for the retry would be wasted.

The present invention solves such a conventional problem, and performs a retry response to the current bus master only when the response from the slave is slow or when there is a bus use request from another bus master. It is another object of the present invention to prevent a decrease in bus throughput by avoiding an overhead for useless retries.

[0009]

FIG. 1 is a diagram illustrating the principle of the present invention. In FIG. 1, 10 is a bus bridge, 101 is a response time monitoring means, A and B are buses, A11 and A12 are bus masters, and B21 is a bus slave.

The present invention is configured as follows to solve the above-mentioned conventional problems. (1): In the bus bridge 10 connecting the bus A to which the bus master A11 is connected and the bus B to which the bus slave B21 is connected, a response time for monitoring the bus bridge 10 for a response time from the bus slave B21. When the bus master A11 accesses the bus slave B21 via the bus bridge 10, the response time monitoring means 101 does not receive an access completion response from the bus slave B21 within a predetermined time. Is detected, a retry is transmitted to the bus master A11 to release the bus A. If an access completion response is detected within the predetermined time, the bus master A1 is detected.
1 keeps the bus A held.

(2): Bus A to which bus masters A11 and A12 are connected and bus B to which bus slave B21 is connected
A bus master right request monitoring means for monitoring a bus master right request in the bus bridge 10, and when the bus master A11 accesses the bus slave B21 via the bus bridge 10, When the bus master right request monitoring means detects a request to use the same bus by a bus master A12 other than the currently accessed bus master A11, the bus master right request monitoring means transmits a retry to the currently accessed bus master A11 and Release bus A.

(3) In the bus bridge of (1) or (2), a bus arbitration unit is provided in the bus bridge 10, and the bus arbitration unit arbitrates the right to use the buses A and B. (Operation) The operation based on the above configuration will be described.

When the bus master A11 accesses the bus slave B21 via the bus bridge 10, the response time monitoring means 101 in the bus bridge 10 confirms that there is no access completion response from the bus slave B21 within a predetermined time. If detected, a retry is transmitted to the bus master A11 to release the bus A. If an access completion response is detected within the predetermined time, the bus master A11 keeps the bus A held. For this reason, a retry response is made to the current bus master A11 only when the response from the bus slave is slow, so that useless retry overhead can be avoided as compared with the conventional delayed transaction method, and a decrease in bus throughput can be prevented.

The bus master A11 is connected to the bus bridge 1
0 to access the bus slave B21 via
When the bus master right request monitoring means in the bus bridge 10 detects a request to use the same bus other than the currently accessed bus master A11, a retry is transmitted to the currently accessed bus master A11. To release the same bus A. For this reason, a retry response is sent to the current bus master A11 only when there is a bus use request from another bus master, so that unnecessary overhead for retry can be avoided as compared with the conventional delayed transaction method, and a decrease in bus throughput is prevented. it can.

Further, a bus arbitration unit is provided in the bus bridge 10, and the bus arbitration unit arbitrates the right to use the buses A and B. Therefore, bus arbitration can be performed inside the bus bridge 10, and a retry response to the bus master A11 can be efficiently performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 2 to 7 are views showing an embodiment of the present invention. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (1): Description of two types of bus connections FIG. 2 is an explanatory diagram of two types of bus connections. In FIG. 2, a bus bridge 10 connects two types of buses A and B. A plurality of bus masters A11, A
12 and A13 are connected to a plurality of bus slaves A21 and A22. The bus B includes a plurality of bus masters B11,
B12 and a plurality of bus slaves B21 and B22 are connected.

The bus bridge 10 connects the bus A and the bus B, and the bus masters A11, A12, A13 are connected to the bus slaves B21, B22 via the bus bridge 10.
And bus masters B11 and B12 are bus slaves A21,
A22 can be accessed.

The bus A has bus masters A11, A12, A
13 transmits and receives data to and from the bus slaves A21 and A22 by outputting address and control signals on this bus. Bus B is bus master B1
1 and B12 transmit and receive data to and from the bus slaves B21 and B22 by outputting address and control signals on this bus.

The bus masters A11, A12, and A13 are bus masters (for example, processors) on the bus A, and can access a bus slave directly connected to the bus. The bus slaves A21 and A22 are bus slaves of the bus A (for example, a memory and an I / O controller), and the bus masters A11, A12, and A on the bus A
13 to transmit and receive data in accordance with a request from the H.13.

The bus masters B11 and B12 are bus masters on the bus B and can access a bus slave directly connected to the bus. Bus slave B
Reference numerals 21 and B22 denote bus slaves of the bus B, which transmit and receive data according to requests from the bus masters B11 and B12 on the bus.

(2) Description of Bus Bridge FIG. 3 is an explanatory diagram of the bus bridge. In FIG. 3, a bus A and a bus B are connected above and below the bus bridge 10, respectively. The bus bridge 10 includes bus arbitration circuits 11 and 12, state machines 13 and 14, bus signal control circuits 15 and 16, address commands, and data buffers 17 and 18.

This bus bridge 10 is a block diagram for realizing a typical delayed transaction. The bus arbitration circuit 11 includes a bus master A1 connected to the bus A.
1, the bus use request signals from A12 and A13 are received and a bus A use permission signal is responded according to a predetermined priority. The bus arbitration circuit 12 receives a bus use request signal from the bus masters B11 and B12 connected to the bus B, and responds with a bus B use permission signal according to a predetermined priority.

The state machine 13 is a state machine of the bus A. When the bus bridge 10 becomes a master of the bus A or is selected by another master as a slave, the operation of the bus A is performed according to the protocol of the bus A. The control for performing is performed. State machine 14
Is a state machine of the bus B, and the bus bridge 10
When the device becomes a master of the bus B or is selected as a slave by another master, the control for operating the bus B is performed according to the protocol of the bus B.

The bus signal control circuit 15 is connected to an external bus A
Is transmitted to the state machine 13 and a signal is output to an external bus A in accordance with an instruction from the state machine 13. The bus signal control circuit 16 transmits an input signal from the external bus B to the state machine 14, and outputs a signal to the external bus B according to an instruction from the state machine 14.

Address command, data buffer 17
Stores information on bus transactions issued by external bus masters A11, A12, and A13. The address command and data buffer 18 stores information on bus transactions issued by the external bus masters B11 and B12.

Although the bus arbitration circuits 11 and 12 are provided inside the bus bridge 10, the bus arbitration circuits 11 and 12 can efficiently perform a retry response to the bus master. However, they can be provided outside the bus bridge 10.

(Explanation of Operation Example of Bus Bridge) A case where the bus master A11 on the bus A makes a read access to the bus slave B21 of the bus B will be described as an example.

First, the bus master A11 on the bus A sends a bus use request to the bus arbitration circuit 11 to start a bus transaction.
Issued to the bus arbitration section of When the bus arbitration circuit 11 confirms that the current bus transaction has been completed and no other bus master having a higher priority has given a request, the bus arbitration circuit 11 responds to the master A 11 with permission to use the bus.

When the bus master A11 acquires the right to use, the bus master A11 outputs attribute (attribute) information including information such as an address, a read, and a size to the bus A. Bus bridge 1
0 confirms that the bus master A11 has read access to the bus slave B11 on the bus B from this information, and sends the identification information of the bus master A11, the address of the bus, and the attribute information to the address command and the buffer of the data buffer 17. Store. Further, a bus use request is issued to the bus arbitration circuit 12 to access the bus B.

At this time, the bus A is occupied by the bus master A11.
The bus bridge 10 issues a retry response to the bus master A11, requesting that the bus A be released and that the same bus transaction be issued later.

Bus Bus Access Based on the address command and the information stored in the buffer of the data buffer 17, the bus bridge 10 starts a bus B transaction upon acquiring the right to use the bus B.
When the read data from the bus slave B11 is output to the bus B, the data is stored in a corresponding area in the buffer of the address command and data buffer 17.

The bus master A11 having received the retry response from the bus bridge 10 once releases the bus A, and starts the same bus transaction again. After acquiring the right to use the bus, the bus master A11 outputs the same address and attribute information as before to the bus A.

When the bus bridge 10 confirms that the address command, the identification information, address, and attribute information of the bus master A 11 stored in the buffer of the data buffer 17 match the current information of the bus A, the bus B Without accessing the address command,
The data stored in the buffer of the data buffer 17 is output to the bus A and responds to the bus master A11.

In this operation, the bus master A of the bus A
While the bus 11 has once released the bus A, another bus master can use the bus A, so that the bus use efficiency is improved.

(3): Description of the time monitoring method In the time monitoring method, a time monitoring mechanism, which is time monitoring (timer monitoring) means, is mounted inside the bus bridge, and a response from the bus slave is returned even after a certain time has elapsed. If not completed, a delayed transaction is performed by returning a retry response to the bus master. Then, if there is a response from the bus slave within this fixed time, the transfer is performed while holding the bus.

FIGS. 4 and 5 illustrate the time monitoring method. FIG. 4 is an explanatory diagram when there is no response to the completion of access within a certain time, and FIG. 5 is a diagram when there is a response to the completion of access within a certain time. FIG. Hereinafter, description will be given with reference to FIGS.

Description of a case where there is no access completion response from the bus master within a predetermined time With reference to FIG. 4, a case where the bus master A11 on the bus A accesses the bus slave B21 of the bus B will be described as an example.

T1: Acquisition of right to use the bus First, the bus master A11 on the bus A sends a bus use request to the bus bridge 10 to start a bus transaction.
Issued to the bus arbitration unit of the bus A. This bus arbitration unit
After confirming that the current bus transaction has been completed and that no other bus master with higher priority has issued a request,
A bus use permission is returned to the master A11.

T2: Start of Bus Transaction When the bus master A11 obtains the right to use, it outputs address and data attribute information to the bus A,
Wait for a response from the bus bridge 10.

T3: Acquisition of right to use bus of bus B The bus bridge 10 obtains the bus master A11 from the above information.
Confirms that the bus master B11 is accessing the bus slave B11 on the bus B, stores the identification information of the bus master A11, the address of the bus, and the attribute information in the buffer of the bus bridge 10 and accesses the bus B in order to access the bus B. Issues a bus use request to the bus arbitration unit.

T4: Access to Bus B When the bus bridge 10 acquires the right to use the bus B, it starts a transaction for the bus B. There is no completion response from the bus slave B11 even after the fixed time t0 has elapsed.

T5: Retry response At this time, the bus A is occupied by the bus master A11.
The bus bridge 10 issues a retry response to the bus master A11, requesting that the bus A be released and that the same bus transaction be issued later.

Description of a case where there is an access completion response from the bus master within a predetermined time With reference to FIG. 5, a case where the bus master A11 on the bus A accesses the bus slave B21 of the bus B will be described as an example.

T1: Acquisition of the right to use the bus First, the bus master A11 on the bus A sends a bus use request to the bus bridge 10 to start a bus transaction.
Issued to the bus arbitration unit of the bus A. This bus arbitration unit
After confirming that the current bus transaction has been completed and that no other bus master with higher priority has issued a request,
A bus use permission is returned to the master A11.

T2: Start of Bus Transaction When the bus master A11 acquires the right to use, it outputs address and data attribute information to the bus A,
Wait for a response from the bus bridge 10.

T3: Acquisition of right to use bus of bus B The bus bridge 10 obtains the bus master A11 from the above information.
Confirms that the bus master B11 is accessing the bus slave B11 on the bus B, stores the identification information of the bus master A11, the address of the bus, and the attribute information in the buffer of the bus bridge 10 and accesses the bus B in order to access the bus B. Issues a bus use request to the bus arbitration unit.

T4: Access to Bus B When the bus bridge 10 acquires the right to use the bus B, it starts a transaction for the bus B. There is a response signal Ack from the bus slave B11 within the fixed time t0.

T5: Completion of Access The bus bridge 10 does not issue a retry response to the bus master A11, performs transfer while the bus master A11 occupies the bus A, and completes the access.

The fixed time t0 varies depending on the adjustment of the system. For example, the fixed time t0 can be set to a time slightly longer than the response time of the bus slave when it is idle (when it is not doing its original work). .

As described above, in this time monitoring method, a retry response is issued to the current bus master only when the response from the bus slave is slow, so that unnecessary overhead for retry can be avoided as compared with the conventional delayed transaction method. A decrease in throughput can be prevented.

(4): Description of the bus master request monitoring method In the bus master request monitoring method, a monitoring mechanism for bus master right requests from all bus masters is mounted in the bus bridge, and a certain bus master accesses a bus slave via the bus bridge. During this time, the bus master request from another bus master is monitored, and if there is no request, the transfer is continuously performed (without performing a retry response and holding the bus). If a request from another bus master is detected, a retry is transmitted to the current bus master to temporarily release the bus.

FIG. 6 is an explanatory diagram of a bus master request monitoring system.
FIG. 7 is a time chart of the bus master request monitoring method. Hereinafter, description will be given with reference to FIGS. : Description of Two Types of Bus Connections In FIG. 6, a bus bridge 10 connects two types of buses A and B. The bus A includes a plurality of bus masters A11, A12, A13 and a plurality of bus slaves A21,
A22 is connected. The bus B includes a plurality of bus masters B11 and B12 and a plurality of bus slaves B21 and B22.
Is connected.

The bus bridge 10 has a bus master right request monitoring mechanism 102 mounted thereon, and the bus masters A11, A12, A13, B11, and B12 notify bus master request signals different from the buses A and B, respectively. Means (shown in dotted lines) are provided.

Description of Time Chart A case where the bus master A11 on the bus A accesses the bus slave B21 on the bus B will be described with reference to FIG.

T1: Acquisition of right to use the bus First, the bus master A11 on the bus A issues a bus use request to the bus bridge 10 to start a bus transaction.
Issued to the bus arbitration unit of the bus A. This bus arbitration unit
After confirming that the current bus transaction has been completed and that no other bus master with higher priority has issued a request,
A bus use permission is returned to the master A11.

T2: Start of Bus Transaction Upon acquiring the right to use, the bus master A11 outputs address and data attribute information to the bus A,
Wait for a response from the bus bridge 10.

T3: Acquisition of right to use bus B The bus bridge 10 obtains the bus master A11 from the above information.
Confirms that the bus master B11 is accessing the bus slave B11 on the bus B, stores the identification information of the bus master A11, the address of the bus, and the attribute information in the buffer of the bus bridge. Issues a bus use request to the arbitration unit.

T4: Access to Bus B When the bus bridge 10 acquires the right to use the bus B, it starts a bus B transaction.

T5: Bus Use Request from Another Bus Master A bus use request is issued from another bus master (for example, bus master A12) before the access by the bus master 11 is completed.

T6: Bus Bridge Retry Response The bus master right request monitoring mechanism 102 detects a bus use request from another bus master A12. At this time, the bus A is occupied by the bus master A11.
0 issues a retry response to the bus master A11 to request that the bus A be released and that the same bus transaction be issued later.

As described above, in this bus master request monitoring method, a retry response is sent to the current bus master only when there is a bus use request from another bus master.
As compared with the conventional delayed transaction method, unnecessary overhead for retry can be avoided, and a decrease in bus throughput can be prevented.

[0062]

As described above, the present invention has the following effects. (1): When the bus master accesses the bus slave via the bus bridge and the response time monitoring means in the bus bridge detects that there is no access completion response from the bus slave within a predetermined time, the bus master A retry is transmitted to release the bus, and if an access completion response is detected within the predetermined time, the bus master keeps holding the bus. Since a retry response is sent to the bus master, unnecessary overhead for retry can be avoided as compared with the conventional delayed transaction method, and a decrease in bus throughput can be prevented.

(2): When the bus master accesses the bus slave via the bus bridge, the bus master right request monitoring means in the bus bridge requests that a bus master other than the bus master currently accessing use the same bus. Is detected, a retry is transmitted to the currently accessed bus master to release the bus, so that a retry response is made to the current bus master only when there is a bus use request from another bus master. ,
As compared with the conventional delayed transaction method, unnecessary overhead for retry can be avoided, and a decrease in bus throughput can be prevented.

(3): A bus arbitration unit is provided in the bus bridge, and the bus arbitration unit performs arbitration of the right to use the bus. Therefore, bus arbitration can be performed inside the bus bridge, and a retry response to the bus master can be efficiently performed. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of two types of bus connections in the embodiment.

FIG. 3 is an explanatory diagram of a bus bridge in the embodiment.

FIG. 4 is an explanatory diagram in a case where an access completion response is not received within a predetermined time according to the embodiment;

FIG. 5 is an explanatory diagram in a case where an access completion response is received within a predetermined time according to the embodiment;

FIG. 6 is an explanatory diagram of a bus master request monitoring method according to the embodiment.

FIG. 7 is a time chart of a bus master request monitoring method according to the embodiment.

[Explanation of symbols]

 Reference Signs List 10 bus bridge 101 response time monitoring means A, B bus A11, A12 bus master B21 bus slave

Claims (3)

[Claims] 1. A bus bridge for connecting a bus to which a bus master is connected and a bus to which a bus slave is connected, the bus bridge comprising: a response time monitoring means for monitoring a time of a response from the bus slave; When the bus master accesses the bus slave via the bus bridge, when the response time monitoring unit detects that there is no access completion response within a predetermined time from the bus slave, it retrys the bus master. A bus bridge, wherein the bus is transmitted to release the bus, and when an access completion response is detected within the predetermined time, the bus master keeps holding the bus. 2. A bus bridge for connecting a bus to which a bus master is connected and a bus to which a bus slave is connected, the bus bridge comprising: a bus master right request monitoring means for monitoring a bus master right request; When accessing a bus slave via the bus bridge, when the bus master right request monitoring means detects a request to use the same bus by a bus master other than the bus master currently being accessed, the bus master right request monitoring means A bus bridge, wherein a retry is transmitted to a bus master to release the same bus. 3. The bus bridge according to claim 1, further comprising a bus arbitration unit in the bus bridge, wherein the bus arbitration unit arbitrates the right to use the bus.