JPH11232216A - Bus arbitration method and bus system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten idle time by effectively utilizing a bus when there is no free area in a receiving data butter. SOLUTION: A slave agent 21 requests bus use to a master agent 11 by a bus request signal 211 . When an address buffer busy signal 14 indicates the existence of a free area in a receiving address buffer 121 , a bus arbitration circuit 111 sends a bus ground signal 221 to permit the use of the bus. When a data buffer busy signal 15 indicates no existence of a free area in a data buffer 131 , the slave agent 21 transfers only an addrses to the master agent 11 through the bus at first. When the signal 15 indicates the existence of a free area in the buffer 13. therearefer, the slave agent 121 transfers data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bus system, and more particularly to a bus system which receives a bus request from a plurality of lower-level agents connected via a single bus, determines a priority order by a centralized arbitration scheme, and uses the bus to transmit data. The present invention also relates to a bus arbitration method and apparatus for a bus system including an upper-level agent for transferring an address and receiving the received data in a reception data buffer and a reception address buffer, respectively.

[0002]

2. Description of the Related Art Conventionally, in the bus arbitration method of this type of bus system, the state of an address / data buffer on the receiving side is monitored when arbitration is performed. Control is performed so that the agent cannot acquire the bus.

[0003]

In the conventional bus arbitration method described above, when a transfer involving data from a plurality of lower agents is attempted, the reception data buffer runs out of space, and even if the reception address buffer has room, There is a disadvantage that the request cannot be accepted and the bus cannot be used. In order to avoid this, a technique has been devised to provide a dedicated line for a read request and receive a read request when there is no space in the reception data buffer and there is room in the reception address buffer, but there is a problem such as an increase in the number of signal lines. Was.

An object of the present invention is to receive a request using a bus when there is no free space in a reception data buffer and a free space in a reception address buffer without increasing the number of signal lines such as dedicated lines for read requests. To provide a bus arbitration method and apparatus that can be used.

[0005]

According to the bus arbitration method of the present invention, a bus use request is received from a plurality of lower agents connected via a single bus to an upper agent having a reception address buffer and a reception data buffer. Performing a centralized arbitration-type bus arbitration from among the plurality of lower-level agents to determine a lower-level agent to acquire a bus, and granting use of the bus; Transferring an address and data from the agent to the upper-level agent using the bus, wherein the received data buffer has no free space and the received address buffer has free space. There is a step of first transferring only the address from the lower agent.

With this configuration, only the address can be transferred first, so that the bus idle time can be reduced, and processing such as address conversion and prefetch can be performed prior to data transfer.

[0007] The step of first transferring only the address includes:
Sending a receive data buffer busy signal and a receive address buffer busy signal indicating whether or not the receive data buffer and the receive address buffer are empty, and receiving the receive address buffer busy signal to the receive address buffer. When it is detected that there is a vacancy, a lower agent for acquiring the bus is determined by bus arbitration, and a bus use permission signal is transmitted to the lower agent. When receiving a data buffer busy signal and detecting that there is no free space in the reception data buffer, the method may further include first transferring only the address to the higher-level agent using the bus.

In the step of transferring only the address first by the lower-level agent, the lower-level agent confirms that there is no free space in the reception data buffer based on the reception data buffer busy signal received by the lower-level agent, and starts transferring only the address. If the address transfer is a transfer without data, release the bus after transferring the address and terminate the transfer.If the transfer involves data, release the bus after transferring the address and temporarily release the bus. The data transfer is performed after the reception data buffer busy signal indicates that there is free space in the reception data buffer, and from the start of the transfer of the address to the end of the data transfer, the upper-level agent performs another transfer. Includes those that control not to accept bus requests from lower-level agents.

A bus system according to the present invention comprises: a plurality of lower agents; a bus; a reception data buffer connected to the plurality of lower agents via the bus and storing data transferred from the lower agents; A receiving address buffer in which an address transferred from the lower agent is stored, and receiving a bus request signal from the lower agent, arbitrating by a centralized arbitration method to determine a lower agent to acquire a bus, and A bus arbitration circuit that grants a bus use permission to the lower agent and transfers data and addresses to the lower agent via the bus.
The lower-level agent transfers only the address to the higher-level agent first using the bus if the received data buffer has no free space when the bus use permission is given and there is a free space in the received address buffer.

[0010] The reception data buffer sends a reception data buffer busy signal indicating whether or not there is free space for storing reception data.
The bus arbitration circuit sends out a reception address buffer busy signal indicating whether or not there is a free space in which a reception address is stored, and the bus arbitration circuit receives the reception address buffer busy signal to detect that there is a free space in the reception address buffer. Then, the lower agent which should acquire the bus by adjusting the bus is determined, and a bus use permission signal is transmitted to the lower agent. The lower agent receives the bus use permission signal when receiving the bus use permission signal. When the receive data buffer busy signal transmitted by the buffer is received and the receive data buffer busy signal indicates that the receive data buffer has no free space, only the address using the bus is used first and the upper-level agent is used. May be transferred.

The lower agent receives the reception data buffer busy signal when receiving the bus use permission signal, confirms that the reception data buffer has no free space, starts transferring only the address, and starts the address transfer. In the case of transfer without data, the bus is released after transferring the address and the transfer is terminated.In the case of transfer with data, the bus is released once after transferring the address,
The data transfer is performed after the reception data buffer busy signal from the upper agent indicates that the reception data buffer is empty, and the bus arbitration circuit transfers the data after the lower agent starts the transfer of the address. Until the end, the control is performed so as not to accept a bus request from another lower agent.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a flowchart of a bus arbitration method according to a first embodiment of the present invention.

In the bus arbitration method shown in FIG. 1, the upper agent first receives a bus use request from a plurality of lower agents (step S1). Next, it is determined whether or not there is a free space in the reception address buffer of the upper agent (step S2). If there is no free space, the process ends without arbitrating the bus (step S3). If there is a free space in the reception address buffer, the bus arbitration is performed to determine a lower agent to acquire the bus, and the lower agent is permitted to use the bus (step S4). Subsequently, it is determined whether or not there is a free space in the reception data buffer of the upper agent (step S5). If there is a free space, the address and data are transferred to the lower agent permitted to use the bus using the bus (step S5). S6). If there is no free space in the received data buffer in step S5, the lower agent transfers only the address first using the bus (step S7).

In the bus arbitration method according to the present embodiment, when there is no free space in the received data buffer and there is a free space in the received address buffer, the address is transferred first, so that the free time of the bus is shortened. And prefetching can be performed prior to data transfer.

FIG. 2 is a flowchart of a bus arbitration method according to a second embodiment of the present invention.

In the bus arbitration method shown in FIG. 2, first, similarly to step S1 in FIG. 1, the upper agent receives a bus use request from a plurality of lower agents (step S1).
1). Next, it sends a receive data buffer busy signal indicating whether there is room in the receive data buffer for storing data, and a receive address buffer indicating whether there is room for storing the address in the receive address buffer. A busy signal is transmitted (step S12). Subsequently, it is determined whether the reception address buffer busy signal indicates that the reception address buffer is empty (step S1).
3) If there is no free space, the bus arbitration is stopped in the same manner as in step S3 of FIG. 1 (step S14). A signal is sent (step S15). Subsequently, it is determined whether the reception data buffer busy signal indicates that the reception data buffer has a free space (step S16). If there is a free space, the address and data are transferred to the lower agent that has received the bus use permission signal (step S16). S17). In step S16, if there is no free space in the reception data buffer, only the address is first transferred to the lower agent that has received the bus use permission signal (step S1).
8).

In the bus arbitration method of this embodiment, as in the case of FIG. 1, when there is no free space in the reception data buffer, the address is transferred first, so that the bus free time is shortened.
Necessary processing such as address conversion and prefetch can be performed in advance.

FIG. 3 is a flowchart of a bus arbitration method according to a third embodiment of the present invention.

In the bus arbitration method of FIG. 3, steps S21 to S27 are the same as steps S11 to S17 of FIG. 2, but if there is no free space in the reception data buffer in step S26, only the address is transferred to the bus. After transferring the data to the upper agent using the bus, the bus is once released (step S28), and the received data buffer busy signal indicates that the received data buffer is free, and then the data is transferred to the upper agent using the bus. (Step S29). From the start of address transfer in step S28 to the end of data transfer in step S29, the upper agent does not respond to a bus use request from another lower agent (step S3).
0).

In the bus arbitration method of the present embodiment, as in the case of FIG. 2, when there is no free space in the reception data buffer, only the address is transferred first, so that the free time of the bus is reduced, and necessary address conversion and Processing such as prefetch can be performed prior to data transfer.

FIG. 4 is a block diagram of a bus system to which the bus arbitration method of FIG. 1 is applied.

The bus system shown in FIG.
And lower agents 2, 3, 4 and 5 and a bus (not shown). The lower agents 2, 3, 4 and 5 are connected to the upper agent 1 via the bus. The upper agent 1 includes a bus arbitration circuit 11, a reception address buffer 12, and a reception data buffer 13. The received address buffer 12 stores the addresses transferred from the lower agents 2, 3, 4, and 5. The received data buffer 13 stores data transferred from the lower agents 2, 3, 4, and 5. The bus arbitration circuit 11 receives bus request signals 21, 31, 41 and 51 requesting permission of bus use from the lower agents 2, 3, 4 and 5, respectively, and when there is no space to be stored in the reception address buffer 12, Do not arbitrate for the bus. At this time, if there is a free space in the reception address buffer 12, the bus arbitration circuit 11 arbitrates the bus in the centralized arbitration system, determines the lower agent to acquire the bus according to the priority, and gives the lower agent the bus use. A bus grant signal 22, 32, 42 or 52 is sent to authorize use of the bus. Bus grant signal 22, 32, 42 or 5
The lower agents 2, 3, 4 or 5 receiving 2 transfer the address and data to the upper agent using the bus if there is a free space in the received data buffer 13, and if there is no free space in the received data buffer 13, Only forward addresses first.

In this bus system, even if there is no vacancy in the reception data buffer of the upper agent, if there is a vacancy in the reception address buffer, only the transfer of the address is performed first, so that the vacancy time of the bus is shortened and the data transfer is performed. Prior to this, processing such as address conversion and prefetch can be performed.

FIG. 5 is a block diagram of a bus system to which the bus arbitration method of FIGS. 2 and 3 is applied.

The bus system shown in FIG.
₁ And subordinate agent 2₁ , 3₁ , 4₁ And 5₁ And ba
(Not shown).₁ ,
3₁, 4₁ And 5₁ Is the upper agent via the bus
1₁ It is connected to the. Top Agent 1₁ Is a bus style
Stop circuit 11₁ And reception address buffer 12₁ And received data
Buffer 13₁ And Receive address buffer
A12₁ Has lower agent 2₁ , 3₁ , 4₁ and
5₁ The address transferred from is stored in its own buffer.
Address indicating whether there is free space to store the address
A sbuffer busy signal 14 is transmitted. Receive data buffer
Fa 13₁ Has lower agent 2₁ , 3₁ , 4₁ And
And 5₁ The data transferred from is stored in its own buffer.
Data bar that indicates whether there is free space for data storage
A buffer 15 is transmitted. Subordinate Agent 2
₁ , 3₁ , 4₁ And 5₁ Are the top agents
1 ₁ Bus request signal 21 requesting the use of a bus
₁ , 31₁ , 41₁ And 51₁ Is sent. Top A
Gent 1₁Bus arbitration circuit 11₁ Is a bus request
Signal 21₁ , 31₁ , 41₁ And 51₁ Accept
Address buffer 12₁ Address buffer sent by
When the busy signal 14 is received, the address buffer busy
Signal 14 is received address buffer 12₁ Address
If there is no room to store, no bus arbitration is performed. This
If there is free space in the receive address buffer,
Arbitration circuit 11₁ Is a centralized arbitration scheme
To arbitrate for buses and get buses according to priority
Determine the next agent and bus to its subordinate agents
Bus grant signal 22 that permits use₁ , 32₁ , 42
₁Or 52₁ To allow use of the bus. Lower d
Agent 2₁ , 3₁ , 4 ₁ Or 5₁ Is the upper age
1₁ From the bus grant signal 22₁ , 32₁ , 42₁ 
Or 52₁ , The upper agent 1₁ From
Receives data buffer busy signal 15 and
Buffa 13₁ If it detects that there is free space, the address and
Higher-level agent 1 using the data bus₁ Forward to
And the reception data buffer 13₁ Detect that there is no free space
If you do, only the address will be sent to the upper agent₁Forward to
I do. The bus arbitration method shown in FIG.
Is applied, subordinate agent 2₁ , 3
₁ , 4₁ Or 5₁ Only the address is the upper agent
1₁When the transfer is completed, the bus is released once the transfer is completed
And the received data buffer busy signal 15 is received.
Data buffer 13₁ Check that there is room
After knowing, the data is transferred to upper agent 1₁ Forward to
You. In this case, upper agent 1₁Bus arbitration circuit 1
1₁ Is the lower agent 2₁ , 3₁ , 4₁ Or 5₁ 
Starts transferring only addresses and then transfers data
Until the end, the bus transfer from other lower agents
Quest signal 21₁, 31₁ , 41₁ And 51₁ By
Control that does not respond to a bus use request.

In this bus system, similarly to the bus system of FIG. 4, even if there is no free space in the reception data buffer of the upper agent, if there is a free space in the reception address buffer, only the transfer of the address is performed first. The time can be shortened, and processing such as address conversion and prefetch can be performed prior to data transfer.

[0028]

As described above, according to the present invention, when there is no vacancy in the reception data buffer of the upper-level agent, if there is vacancy in the reception address buffer, only the address is transferred by the bus, so that the vacancy time of the bus is reduced. Since the address can be shortened for effective use, and the address is transferred prior to the data transfer, processing such as address conversion and prefetch can be performed, thereby improving the processing efficiency of the information processing apparatus.

[Brief description of the drawings]

FIG. 1 is a flowchart of a bus arbitration method according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a bus arbitration method according to a second embodiment of the present invention.

FIG. 3 is a flowchart of a bus arbitration method according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a bus system to which the bus arbitration method of FIG. 1 is applied.

FIG. 5 is a block diagram of a bus system to which the bus arbitration method of FIGS. 2 and 3 is applied;

[Explanation of symbols]

1, 1 ₁ Upper agent 2, 2 ₁ , 3, 3 ₁ , 4, 4 ₁ , 5, 5 ₁ Lower agent 11, 11 ₁ Bus arbitration circuit 12, 12 ₁ Receive address buffer 13, 13 ₁ Receive data buffer 14 Address Buffer busy signal 15 Data buffer busy signal 21, 21 ₁ , 31, 31 ₁ , 41, 41 ₁ , 51, 51 ₁
Bus request signals 22, 22 ₁ , 32, 32 ₁ , 42, 42 ₁ , 52, 52 ₁
Bus grant signal

Claims (6)

[Claims] A step of receiving a bus use request from a plurality of lower agents connected via one bus to an upper agent having a reception address buffer and a reception data buffer; Arbitrating bus arbitration to determine a lower-level agent to acquire the bus and give permission to use the bus; and A bus arbitration method for a bus system, comprising the step of: transferring the address only from the lower agent first when the reception data buffer has no space and the reception address buffer has a space. A bus arbitration method comprising: 2. The method according to claim 1, further comprising: transmitting a reception data buffer busy signal and a reception address buffer busy signal indicating whether or not the reception data buffer and the reception address buffer have free space, respectively. Receiving the reception address buffer busy signal and detecting that there is free space in the reception address buffer,
Determining a lower agent to acquire a bus by bus arbitration, and transmitting a bus use permission signal to the lower agent; the lower agent receiving the bus use permission signal receiving the reception data buffer busy signal and 2. The bus arbitration method according to claim 1, further comprising, when detecting that there is no free space in the reception data buffer, first transferring only the address to the upper-level agent using the bus. 3. The method of claim 1, wherein the lower agent first transfers only the address. The lower agent confirms that there is no free space in the reception data buffer based on the reception data buffer busy signal received by the lower agent and starts transferring only the address. In the case where the address transfer is a transfer without data, the bus is released after transferring the address and the transfer is terminated, and in the case of a transfer with data, the bus is once released after transferring the address, The upper agent transfers the data after the reception data buffer busy signal from the upper agent indicates that the reception data buffer is empty, and, from the start of the address transfer to the end of the data transfer, 3. The bus arbitration method according to claim 2, wherein control is performed so as not to accept a bus request from another lower agent. 4. A plurality of lower agents, a bus, a reception data buffer connected to the plurality of lower agents via the bus and storing data transferred from the lower agents, and a transfer from the lower agents. When a bus request signal is received from the lower-level agent, the lower-level agent that performs arbitration by the centralized arbitration method to determine a lower-level agent to acquire the bus and permits the lower-level agent to use the bus. A bus arbitration circuit for transferring the data and the address to the lower agent via the bus, the upper agent comprising a bus arbitration circuit. No space left in buffer A bus system for transferring only an address first to an upper-level agent using the bus when there is a free space in the reception address buffer; 5. The reception data buffer sends a reception data buffer busy signal indicating whether or not there is a space for storing reception data, and the reception address buffer has a space for storing a reception address. When the bus arbitration circuit receives the reception address buffer busy signal and detects that the reception address buffer has a free space, the bus arbitration circuit adjusts the bus and performs bus adjustment. Determines a lower-level agent to obtain the following, sends a bus use permission signal to the lower-level agent, and the lower-level agent transmits a reception data buffer busy signal transmitted by the reception data buffer when the bus use permission signal is received. Receiving, the reception data buffer busy signal indicates that the reception data buffer is full. 5. The bus system according to claim 4, wherein only the address is transferred to the upper agent first using the bus. 6. The lower agent receives the reception data buffer busy signal when receiving the bus use permission signal, confirms that the reception data buffer has no free space, and starts transferring only an address. If the address transfer is a transfer without data, release the bus after transferring the address and terminate the transfer.If the transfer involves data, release the bus after transferring the address and temporarily release the bus. Transfer data after the receive data buffer busy signal from the device indicates that there is free space in the receive data buffer, and the bus arbitration circuit terminates the data transfer after the lower agent starts transferring the address. 6. The bus system according to claim 5, wherein control is performed so as not to accept a bus request from another lower agent until the request is made.