JP2000099455A - First-come priority bus competition control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a first-come priority bus arbitrating system capable of using buses in the order of bus use request generation without performing bus arbitration according to the fixedly determined priority. SOLUTION: Concerning the bus competition control system for a processor with which plural input/output device are connected to the buses, this system is provided with a first-come fixed priority arbitrating part 2 for performing the priority selection of bus use request signals from the respective input/output devices in the order of arrival for the unit of clock, a change detecting part 3 for detecting the change of priority output from the first-come fixed priority arbitrating part 2, a priority storage part 4 for storing the priority output from the change detecting part 3 until the end of bus use, a bus use permit signal synchronizing part 5 for outputting a bus use permit signal, and an arbitration control part 6 for controlling the output of the bus use permit signal from the bus use permit signal synchronizing part 5 corresponding to the output state of the bus use permit signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a first-come-first-served bus contention control method used for bus contention control in a processing device in which a plurality of input / output devices are connected to a bus.

[0002]

2. Description of the Related Art A conventional bus contention control system will be described with reference to the drawings. FIG. 3 is a block diagram showing a configuration of a conventional bus contention system, and FIG. 4 is an operation time chart in a conventional bus contention system.

Conventionally, a bus contention control system in a processing device in which a plurality of input / output devices are connected by a bus generally has a bus contention system configuration as shown in FIG. Now, assuming that the priority order is fixedly determined in the order of the input / output devices A to D, while the input / output device having the higher priority is using the bus, the other input / output devices having the lower priority are kept waiting, and In this method, a high input / output device performs bus arbitration in accordance with a fixed priority determined at the end of bus use.

More specifically, as seen in the bus contention operation time chart shown in FIG. 4, regardless of the order of arrival of the bus use request signals REQ from the input / output devices A to D,
The clock arrival time T2, time T4, and time T after each bus use end according to the determined fixed priority.
6. Bus arbitration is performed only at time T8. Therefore,
The input / output device D having the determined lower priority has been postponed even though the bus use request has been transmitted between the time T1 and the time T2, and the bus use right cannot be obtained until the time T8.
If a bus use request is periodically generated from the other input / output devices A to C having a higher priority between the time T1 and the time T7, the bus right is not transferred to the input / output device D during that time.

As described above, in the conventional bus contention method, the right to use the bus is not easily transferred to the I / O device having a low priority, and the bus monitoring timer of the I / O device times out during that time. There is.

[0006] On the other hand, with the increase and speeding up of processed data in recent years, it has become difficult to determine the priority itself in accordance with the bus throughput of each input / output device.

[0007]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, it is an object of the present invention to perform bus arbitration in accordance with a fixed priority determined at the end of use of the bus as in the prior art. And a bus arbitration system in which the buses can be used in the order in which the bus use requests are generated.

[0008]

In order to solve the above problem, the first-arrived priority bus arbitration system of the present invention includes a first-arrival fixed priority arbitration unit, a change detection unit, a priority storage unit, and a bus arbitration unit.
By providing an arbitration control unit, first-come-first-served selection is performed in the order of arrival of bus use request signals from each input / output device, and bus use request signals arriving simultaneously within a unit clock are selected by fixed priority. It is characterized in that a bus right is transferred to an input / output device having a low priority in a first-come-first-served order.

According to the present invention, it is possible to prevent a situation in which an I / O device having a higher priority occupies the bus and an I / O device having a lower priority cannot obtain a bus right. The effect is that the right is granted.

[0010]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a bus contention system according to an embodiment of the present invention, and FIG. 2 is an operation time chart in a bus contention according to the embodiment of the present invention.

The features of the bus contention system according to the present embodiment are as follows.
As shown in FIG. 1, the first-come first-served priority arbitration unit 2 selects arbitration for the bus use request signal REQ such that the first-come-first-served order is prioritized in units of one clock, and the precedence of the result of arbitration with the first-come first-served priority over the fixed priority. Are detected by the change detecting unit 3 and the detected priorities are stored in the priority storing unit 4.

In the arbitration control unit 6, the primary bus use permission signal A
Based on the conditions of K1 and the secondary bus use permission signal AK2, output control to the mask signal MSK for inhibiting the input of the bus use request signal to the first-come-first-served priority arbitration unit 2 and the priority order storage unit 4 is performed.

The first-come first-served priority arbitration unit 2 does not perform bus arbitration at the end of use of the bus, but executes first-come first-served selection by a bus use request signal in units of one clock even when the bus is in use. I do. In principle, first-come, first-served selection is performed in the order of arrival of the bus use request signals. However, bus use request signals that arrive at the same time within a unit clock are selected according to a fixed priority.

Referring to FIG. 1, bus use request signals REQ from a plurality of input / output devices (not shown) are transmitted through signal lines 9a to 9a.
The signal is input to the bus request signal synchronizer 1 via 9d. The bus use request signal synchronized with the same clock is signal line 1
It is input to the first-come-first-served priority arbitration unit 2 via 0a to 10d.

The first-arrival fixed priority arbitration unit 2 performs bus arbitration in accordance with a fixed priority determined fixedly and a mask condition from the arbitration control unit 6. The change detection unit 3 detects a change in the output signal from the first-come-first-served priority arbitration unit 2, and when there is a change, stores the arbitration result in the priority order storage unit 4 via the signal lines 11 a to 11 d and performs arbitration control at the same time. The unit 6 is notified of the primary bus use permission state.

The arbitration control unit 6 outputs to the first-come-first-served priority arbitration unit 2 a mask signal 14 for inhibiting input of a bus use request signal from an input / output device for which the primary bus use permission or the secondary bus use permission has been obtained. . Also, when the secondary bus use permission signal ACK2 is negated, the arbitration control unit 6 inputs the output instruction signal 15 to the priority storage unit 4 and outputs the priority signal.

Next, a bus arbitration process according to this embodiment will be described with reference to the drawings.

In FIG. 2, at time T0, input / output device A
Is using the bus. At time T1, since the bus use request signal C-REQ has arrived only from the input / output device C,
The primary bus use permission signal C-AK1 is output to the priority storage unit 4 via the change detection unit 3.

At time T2, a bus use request signal B-REQ from the input / output device B, a bus use request signal C-REQ from the input / output device C, and a bus use request signal D-REQ from the input / output device D
REQ is input. However, as for the input / output device C, since the primary bus use permission signal C-AK1 has already been acquired, the input from the bus request signal synchronizer 1 at the time T1 by the mask signal MSK from the arbitration controller 6 is performed. prohibited. In addition, the bus use request signals arriving at the same time within the unit clock are selected according to the fixed priority, so that the input / output devices B and D
2, the input / output device B is selected first, and the primary bus use permission signal B-AK1 of the input / output device B is output to the change detection unit 3. At the next time T3, the primary bus use permission signal D-AK1 of the input / output device D is output to the change detection unit 3. And
At the time T2, the reception of the bus use request signal REQ from the input / output device B and from the input / output device D at the time T3 are prohibited.

When the secondary bus use permission signal A-AK2 of the input / output device A is negated between the time T1 and the time T2, the bus use of the input / output device C stored in the priority storage unit 4 is permitted. The signal C-AK1 is read, and the secondary bus use permission signal C-AK2 is output at time T2.

Subsequently, when the secondary bus use permission signal C-AK2 of the input / output device C is negated between the time T3 and the time T4, the bus use of the input / output device B stored in the priority storage unit 4 is permitted. The signal B-AK1 is read, and the secondary bus use permission signal B-AK2 is output at time T4. Time T4
As in the case of the input / output device C, the input of the bus use request signal of the input / output device D is prohibited. Time T
5, the bus use request signal C-
Since the REQ has arrived, the primary bus use permission signal C-
At the same time as the output of AK1, the input of the bus use request signal of the input / output device A is prohibited.

When the secondary bus use permission signal B-AK2 of the input / output device B is negated between time T5 and time T6,
The bus use permission signal D-AK1 of the input / output device D stored in the priority storage unit 4 is read out, and at time T6, the input / output device D with the lowest priority is given priority on a first-come, first-served basis, The bus use permission signal D-AK2 is output.

When the secondary bus use permission signal D-AK2 of the input / output device D is negated between time T7 and time T8,
The bus use permission signal A-AK1 of the input / output device A stored in the priority storage unit 4 is read out, and the secondary bus use permission signal A-AK2 is output at time T8.

As another embodiment of the present invention, the basic configuration is the same as that of the above embodiment, but the output instruction from the priority order storage unit 4 triggers the secondary bus use permission signal negation condition. In order to increase the bus arbitration speed by devising it, the bus use request signals 9a to 9d from the input / output device during the assertion of the secondary bus use permission signal are judged to be the end of the bus use, and the priority order storage unit is used. An output instruction may be given.

In each of the above embodiments, the four input / output devices A to D have been described. However, the number of input / output devices is not limited to four and may be any number. For the priority order storage unit, a first-in first-out FIFO is used.
It can be configured by having the same function as.

[0027]

As described above, in the first-come-first-served fixed-priority bus contention control method of the present invention, bus arbitration is not performed when the bus use of an arbitrary input / output device is completed, but one bus is used even when the bus is being used. Since bus arbitration is performed in units of clocks according to the first-come-first-served priority condition, buses can be used in the order in which bus use requests are generated.

Therefore, it is possible to prevent a situation in which an I / O device having a higher priority occupies the bus and an I / O device having a lower priority cannot obtain the bus right, and the bus right is granted in the order in which the bus use request arrives. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a bus contention system according to an embodiment of the present invention.

FIG. 2 is an operation time chart in a bus contention according to the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional bus contention system.

FIG. 4 is an operation time chart in a conventional bus competition.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bus request signal synchronizing part 2 First-arrival fixed priority arbitration part 3 Change detection part 4 Priority storage part 5 Bus use permission signal synchronizing part 6 Arbitration control part 7 I / O device 8 Processing device 20 Bus request signal synchronizing part 21 Fixed Priority arbitration unit 22 bus use permission signal synchronization unit 23 input / output device 24 processing device

Claims (5)

[Claims] In a bus contention control method in a processing device in which a plurality of input / output devices are connected to a bus, a first-come first-served priority arbitration unit that performs priority selection in a clock unit on a bus use request signal from each of the input / output devices. When,
A change detection unit that detects a change in the priority output from the first-come-first-served priority arbitration unit; a priority storage unit that stores the priority output from the change detection unit until the end of bus use; and outputs a bus use permission signal. And a arbitration control unit that controls the output of the bus use permission signal from the bus use permission signal synchronization unit according to the output state of the bus use permission signal. Priority bus contention control method. 2. A fixed priority arbitration unit for performing priority selection based on a predetermined priority when a bus use request signal from each input / output device arrives at the same time within a single clock. The first priority bus contention control system according to claim 1, wherein: 3. The first priority bus contention control system according to claim 1, wherein the first priority fixed priority arbitration unit outputs a primary bus use permission signal to the change detection unit. 4. The first priority bus contention control method according to claim 1, wherein a secondary bus use permission signal is output from the bus use permission signal synchronization unit. 5. The arbitration control unit outputs a mask signal for inhibiting input of a bus use request signal from an input / output device for which a primary bus use permission or a secondary bus use permission has been obtained to a first-come-first-served priority arbitration unit. The first-come-first-served bus contention control method according to any one of claims 1 to 4, wherein: