JPH04106651A - Controller for system bus - Google Patents

Abstract

PURPOSE:To improve the economy and reliability of a system bus by providing busy status holding means which recognizes the busy status of its own device connected to a system bus on the basis of data transfer controlling information to each device connected to the system bus. CONSTITUTION:Busy status holding means 13-16 respectively provided to plural devices 1-4 connected to a system bus 27 recognize the busy status of the devices 1-4 on the basis of data transfer controlling information. Bus arbitration controlling means 9-12 respectively discriminate the busy statuses of transferred devices from the recognized information of the means 13-16 and inhibit the delivery of bus requesting signals from transferring devices when one the transferred devices are busy. Therefore, the economy and reliability of the system bus can be improved, since no special busy signal line is required to the system bus.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a system bus control device that controls a system bus shared by a plurality of devices.

(Prior Art) In a system in which a plurality of devices share a system bus, the plurality of devices are given statically or dynamically set priority rights to use the system bus.

When multiple devices compete for the use of the system bus, arbitration is performed so that the device with higher priority among the multiple devices acquires the right to use the system bus. At this time, if a device with a high priority that has obtained the right to use the system bus accesses a busy device via the system bus, the requested transfer will become a busy response, and new updates will be performed until the busy status is released. Busy retry is repeated unless a device with higher priority issues a request to use the system lot.

Therefore, during this period, effective transfer from a device with a low priority to a device that is not in a busy state is not performed, and the system bus cannot be used effectively.

Conventionally, as a method to avoid invalid system bus usage due to the busy state of the transfer destination, for example, Japanese Patent Laid-Open No.
There is a system bus control method disclosed in Japanese Patent No. 166242.

This system bus control method takes the busy signal output from the busy signal generation circuit of the transfer destination device to the bus translation stop control circuit of the own device via the system bus.
A request to use the system bus is issued only when the destination device is not sending out a busy signal. By using this method, unnecessary system bus accesses are reduced, low-priority devices are given more access opportunities, and system bus efficiency is improved.

(Problem to be Solved by the Invention) However, in the conventional system bus control method described above, busy signals and busy signal lines are required for each device connected to the system bus, and the number of system bus signal lines increases. In addition, there is a problem in that a driver/receiver that is not suitable for LSI is required for each busy signal.

The present invention was made to solve the above problems,
An object of the present invention is to provide an economical system bus control device that does not require a special busy signal line on the system bus.

(Means for Solving the Problems) A system bus control device of the present invention gives different priorities to bus request signals of a plurality of devices sharing a single system bus, so that the bus use requests of the plurality of devices are In the case of contention, a device having a bus request signal with a high priority acquires the right to use the system bus, and in a system bus control device that transfers data between the plurality of devices via the system bus, device-specific busy state holding means, which is provided in each device and recognizes the busy state of all devices connected to the system bus within the device itself based on transfer control information for the data transfer; and the device-specific busy state The busy state of the transfer destination device is determined based on the recognition information of the holding means, and when the transfer destination device is in the busy state, the sending of a bus request signal from the transfer source device is suppressed, and when the transfer destination device is not in the busy state, the bus request signal is not sent. A bus arbitration control means for sending out signals is provided.

(Function) In the system bus control device of the present invention, the device-specific busy state holding means provided in each of the plurality of devices determines the busy state of all devices connected to the system bus based on transfer control information for data transfer. recognize.

Further, the bus arbitration control means determines the busy state of the transfer destination device based on the recognition information of each device and the busy state holding means, and suppresses the transmission of the bus request signal from the transfer source device when the transfer destination device is in the busy state.

Therefore, when a bus use request is issued to multiple devices at the same time, if the device-specific busy state holding means recognizes that each data transfer partner device is not in a busy state, the bus arbitration control means will grant the right to use the system bus. A device with a high priority issues a bus request signal, and a device with a low priority is forced to wait for acquisition of the system bus.

Further, if a certain device is in a busy state, the bus arbitration control means does not send out a bus request signal even if the device attempting to transfer data to that device is a device with a high priority. Therefore, a device with a lower priority is not forced to wait to acquire the right to use the system bus.

Furthermore, since the recognition of whether a device is busy or not is carried out by device-specific busy state maintenance means within the own device based on normal transfer control information, it is possible to recognize whether or not a device is busy by the number of devices connected to the system bus. No signal line is required.

(Example) Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

FIG. 1 is a configuration diagram of an apparatus for explaining the system lotus control method of the present invention.

The device shown in the figure is composed of four devices 1 to 4 and a system bus 27 shared by these devices 1 to 4.

Each of the devices 1 to 4 includes transfer control means 5 to 8, bus arbitration control means 9 to 12, and device-specific busy state holding means 13 to 1.
6, and by these means the system bus 27
is connected to.

The system bus 27 includes a transfer control line 25 and a bus arbitration line 26.
It consists of.

The transfer control line 25 is a collection of signal lines related to data transfer, including address, data, read/write signal lines, and a transfer destination device address line that indicates the transfer destination, and a transfer destination device that identifies the transfer destination. It has an address line and a transfer type control line that indicates transfer activation/report. Further, the transfer control line 25 is connected to the transfer control means 5 to 8 and the device-specific G state holding means 13 to 16.

The bus arbitration line 26 is a set of bus request signal lines and control signal lines corresponding to each device 1-4, and is connected to the bus arbitration control means 9-12 of each device 1-4.

Different priorities are given to bus request signals, and if there is a conflict of bus use requests in each device, each device 1 to 4 The bus arbitration control means 9 to 12 perform distributed control.

In addition, in this embodiment, the priority order of each device 1 to 4 is
Device 2>Device 3>Device 4.

Further, transfer request lines 17 to 8 are sent from transfer control means 5 to 8 of each device 1 to 4 to bus arbitration control means 9 to 12, respectively.
20 are connected. Further, device-specific busy state indication lines 21-24 indicating the busy state of each device are connected from the device-specific busy state holding means 13-16 to the bus arbitration control means 9-12, respectively.

The device-specific busy state holding means 13 to 16 are circuits consisting of decoders, F/Fs (flip-flops), etc., as will be described later, and are circuits that are a feature of the present invention. That is, the transfer control line 25 for normal data transfer is used to monitor the transfer on the system bus 27, the busy state of each device 1 to 4 is set and maintained in the device itself, and the bus arbitration control means 9 to 12
It has a function of outputting information via device-specific busy state indication lines 21 to 24.

The bus arbitration control means 9 to 12 are circuits consisting of priority encoders, decoders, F/Fs, etc., and the transfer control means 5
In response to the transfer request from ~8, the busy status of the transfer destination device is determined based on the information of each device and the busy status holding means 13 to 16, and if it is busy, the transfer request is suppressed, and if it is not busy, the transfer request is suppressed. It has the function of generating a bus request signal and executing bus arbitration.

Further, the transfer control means 5 to 8 are comprised of known control circuits that control normal data transfer.

FIG. 2 shows the specific configuration of each device and the G state holding means 13 to 16.

That is, the device-specific busy state holding means 13 to 16 include a transfer source device decoder 31, a transfer destination device decoder 32, a transfer type decoder 33, and a device-specific busy state holding F/F (hereinafter referred to as
(simply referred to as F/F) 34 to 37.

A source device address line (transfer control line 25) for transmitting transfer control information is connected to the input of the source device decoder 31, and the output is sent via device-specific busy release lines 38 to 41 corresponding to devices 1 to 4. are connected to the reset terminals of F/Fs 34 to 37, respectively. Further, the transfer source device decoder 31 is configured to be enabled by a transfer report signal output from the transfer type decoder 33.

The transfer destination device decoder 32 has an input connected to a transfer destination device address line (transfer control line 25) for transmitting transfer control information, and outputs via device-specific busy setting lines 42 to 45 corresponding to devices 1 to 4. are connected to the set terminals of F/Fs 34 to 37, respectively. Further, the transfer destination device decoder 32 is configured to be enabled by a transfer activation signal output from the transfer type decoder 33.

The transfer type decoder 33 has a transfer type control line (transfer control line 25) connected to its input that transmits transfer control information, and
Its output is connected to the enable terminals of the source device decoder 31 and the destination device decoder 32. Further, this transfer type decoder 33 is configured to be enabled by a strobe signal from a transfer strobe line. still,
This strobe signal is a transfer instruction signal indicating that data such as an address valid for data transfer is being output.

In addition, F/Fs 34 to 37 each have the following outputs:
Device-specific busy state indication signal line 46 corresponding to devices 1 to 4
~49 are connected. These four device-specific busy state indication signals 46 to 49 correspond to any one of the device-specific busy state indication lines 21 to 24 in FIG.

Next, the operation of the above control device will be explained.

First, when a bus request is issued to devices 1 to 4 having different rights to use the system bus at the same time, if each data transfer partner device is not busy, the device with the higher priority of the right to use the system bus 27 will issue the bus request signal. , and devices with lower priority are forced to wait for acquisition of the system bus 27.

For example, if a bus use request is made from device 1 to device 3 to transfer data, and a bus use request is made from device 2 to device 4 to transfer data, device 3 If device 1 is not in a busy state, device 1 outputs a bus request signal, and device 2's bus use request is put on standby.

Next, recognition of the busy state of each device 1 to 4 will be explained.

FIG. 3 shows a time chart of the inter-device transfer operation.

In this embodiment, a transfer operation between devices 1 and 2 will be explained as an example of inter-device transfer.

In FIG. 3, the first half (T1) of the time chart shows how inter-device transfer is performed from device 2 to device 1 via the system bus 27 for starting transfer in response to a transfer strobe signal.

That is, first, the transfer type decoder 33 is enabled by changing the signal on the transfer strobe line shown in FIG. 3(d) from H (high level) to low level. Further, the address data of device 2 is input to the transfer source device address line, the address data of device 1 is input to the transfer destination device address line, and the transfer start data is input to the transfer type control line [Figure 3 (a), (b), (c). As a result, the transfer type decoder 33 decodes the transfer start signal on the transfer type control line and asserts the transfer start, and the transfer destination device decoder 32 is enabled.

Next, the transfer destination device decoder 32 decodes the signal on the transfer destination device address line and decodes the device 1 busy state holding F/F 3.
The device 1 busy setting line 42, which is the set input of 4, is asserted [FIG. 3(e)].

As a result, the F/F 34 of the device 1 is set, and the output device 1 busy state indication signal line 46 comes to indicate that the device N1 is busy [FIG. 3(f)].

While the device 1 is in a busy state, for example, even if a transfer request is generated from the transfer control means 7 of the device 3 to the device I through the transfer request line 19, the device-specific busy state indication line from the device-specific busy state holding means 15 Since the device 1 busy status indication signal line 46 of the 23 signals indicates that the device 1 is busy, the bus arbitration control means 11 can suppress this transfer request.

The second half (T2) of the time chart in FIG. 3 shows the transfer report from device 1 to device 2.

That is, when the transfer type decoder 33 is enabled by the signal on the transfer strobe line, the transfer type decoder 33 decodes the transfer report signal on the transfer type control line, and sends the transfer report signal to the transfer source device decoder 31. This enables the source device decoder 31 and decodes the signal on the source device address line. Note that the address data of device 1 is input to the transfer source device address line, and the address data of device 2 is input to the transfer destination device address line.

As a result, the device 1 busy release line 38 is asserted, the F/F 34 of device 1 is reset, and the 20 F/F 3
The device 1 busy state indication signal line 46, which is the output of device 4, indicates the non-busy state of device l.

Here, if the inhibited transfer request to the device 1 exists in another device, the passnoquest signal can be sent at this point.

In the above embodiment, the transfer operation between device 1 and device 2 has been described, but transfer operation between other devices can be performed in exactly the same manner.

In addition, in the above embodiment, the priority order of bus usage rights for each device 1 to 4 is device 1>device 2>device 3>device 4, but even if the priority order is other than this, the same priority as in the above embodiment may be used. be effective.

(Effects of the Invention) According to the system bus control device of the present invention described above, the device being purchased can monitor the busy states of all devices connected to the system bus within itself based on normal data transfer control information. Since it is equipped with a busy state holding means for each device to be managed, there is no need to provide a special busy signal line on the system bus, and there is no need for a driver/receiver for the busy signal as in the past, making it easy to implement into LSI. Therefore, economical efficiency and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the system bus control device of the present invention, FIG. 2 is a specific configuration diagram of the device-specific busy state holding means of the device of the present invention, and FIG. 3 is the operation of the device of the present invention. This is a time chart. 1-4...device, 5-8...transfer control means, 9-1
2...Bus arbitration control means, 13-16...Busy state holding means, 25...Transfer control line, 26...Bus arbitration line, 27...System bus. Patent applicant Oki Electric Industry Co., Ltd.

Claims (1)

[Scope of Claims] Different priorities are given to bus request signals of a plurality of devices sharing a single system bus, and when the bus use requests of the plurality of devices conflict, the bus request signal has a higher priority. In a system bus control device in which a device acquires the right to use a system bus and transfers data between the plurality of devices via the system bus, the system bus control device is provided in each of the plurality of devices and connected to the system bus. device-specific busy state holding means that recognizes the busy state of all the devices within itself based on the transfer control information of the data transfer; and the busy state of the transfer destination device based on the recognition information of the device-specific busy state holding means. judge,
A system bus characterized in that a bus arbitration control means is provided for suppressing sending of a bus request signal from a transfer source device when the transfer destination device is in a busy state, and sending out a bus request signal when the transfer destination device is not in a busy state. control device.