JP3244044B2 - Bus arbitration method and bus system - Google Patents

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]

Means for Solving the Problems A bus arbitration method according to the present invention includes a reception address buffer and a reception data buffer.
Multiple lower-level agents to a higher-level agent via a single bus.
Agent is connected and the bus is licensed.
Address using the bus from the
A bus system in which data is transferred to the upper agent
In the bus arbitration method, the reception data buffer and the
And receive address buffers have free or no
Receive data buffer busy signal indicating how
Detecting a dress buffer busy signal;
The address buffer busy signal indicates that the received address
When it is detected that there is free space in the
Decide which lower-level agent should get the bus
Sending a bus permission signal to the next agent;
The lower agent that has received the bus use permission signal
(1) before receiving the receive data buffer busy signal
When it is detected that there is free space in the receive data buffer
Uses the bus to transfer addresses and data to the upper
(2) the received data buffer
If it is detected that there is no free space, use the bus
After transferring only the address to the upper agent first
Release the bus once and receive data from the upper agent
Buffer busy signal is empty in the receive data buffer
Transfer data after indicating that there is
From the start of data transfer to the end of data transfer
Means that a higher-level agent is
Control so as not to accept a service request.

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]

[0008]

The bus system of the present invention includes a plurality of lower
Agent, a bus, and the plurality of
Has a higher-level agent connected to the higher-level agent
In the bus system configured by
The data transferred from the subordinate agent is
Indicates whether or not there is free space for data to be stored
Received data buffer Received data that sends a busy signal
Buffer and the address transferred from the subordinate agent.
Address is stored, and there is space to store the received address.
Sends receive address buffer busy signal indicating whether or not
Receiving address buffer, and receiving address buffer
Receive the busy signal and empty the received address buffer.
When it detects that there is a
Receives a bus request signal, arbitrates, and acquires a bus
Determine the lower-level agent to be used and the lower-level agent
A bus arbitration circuit for granting a bus use permission to the
Prior to receiving the bus grant signal.
The receive data buffer transmitted by the receive data buffer
(1) Receive data buffer busy
Signal indicates that the receive data buffer is empty
The address and data using the bus.
To the upper agent, and (2) the received data
Buffer busy signal is empty in the receive data buffer
If there is no bus, use the bus to access
After transferring only the dress to the upper agent first
Release the bus once and receive data from the upper agent
Buffer busy signal is empty in the receive data buffer
Transfer data after indicating that there is a bus arbitration
The lower agent initiates the forwarding of the address.
From the start to the end of data transfer, other lower
Control not to accept bus requests from agents

[0010]

[0011]

[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). If there is a free space, the bus arbitration is performed to determine the lower-level agent to acquire the bus and to permit the bus use. 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 agent 1 first.₁Forward 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
And the received data buffer busy signal 15 is received.
Data buffer 13₁ Check that there is room
After knowing, the data is sent 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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G06F 12 / 00,13 / 16,13 / 36 G06F 13 / 362,13 / 38,15 / 16

Claims (2)

(57) [Claims] (1)Receive address buffer and receive data buffer
To a higher-level agent with
Number of subordinate agents are connected and the bus is licensed
Received from the lower agent using the bus.
Address and data are transferred to the upper agent
In the bus arbitration method of the bus system, The reception data buffer and the reception address buffer
Receive data buffer indicating whether each has free space
Busy signal and receive address buffer busy signal.
Detecting, The reception address buffer busy signal causes the reception
When it detects that there is free space in the dress buffer,
Decide which lower-level agent should get the bus through arbitration
Sends a bus use permission signal to the lower agent
Stages and The lower agent that has received the bus use permission signal
(1) before receiving the receive data buffer busy signal
When it is detected that there is free space in the receive data buffer
Uses the bus to transfer addresses and data to the upper
(2) the received data buffer
If it is detected that there is no free space, use the bus
After transferring only the address to the upper agent first
Release the bus once and receive data from the upper agent
Buffer busy signal is empty in the receive data buffer
Transfer data after indicating that there is
From the start of data transfer to the end of data transfer
Means that a higher-level agent is
Control so as not to accept a service request.
And a bus arbitration method. (2)Multiple sub-agents, buses, and fronts
Connected to the plurality of lower-level agents via a bus.
Bus system configured with a host agent
At The upper agent, The data transferred from the lower agent is stored.
Received, indicating whether there is free space to store the data
Receive data buffer that sends a data buffer busy signal
And The address transferred from the lower agent is stored.
Indicates whether or not there is free space to store the received address.
Receive address buffer
Res buffer and Receiving the reception address buffer busy signal and
When it is detected that there is free space in the
Upon receiving a bus request signal from the lower agent,
Stop to determine the lower agent to get the bus
To give the lower agent a bus permission
With a stop circuit, The lower agent receives the bus use permission signal
When the received data buffer sent by the received data buffer
Receiving a busy signal and (1) receiving data buffer
A busy signal is available in the receive data buffer
Indicates that the address and address are
Transferring the data to the upper-level agent;
Receive data buffer busy signal
If there is no free space in the bus, use the bus
And transfer only the address to the upper agent first.
Release the bus once and receive from the upper agent
A data buffer busy signal is sent to the receive data buffer.
Transfer data after indicating availability, In the bus arbitration circuit, the lower agent
From the start of data transfer to the end of data transfer
Does not accept bus requests from other lower-level agents.
A bus system characterized by control as follows.