JPH057207A - Scsi bus priority sequence evading system by polling - Google Patents

Abstract

PURPOSE:To eliminate the exclusive-using of an SCSI bus by an SCSI device with the highest priority and to equally use the SCSI bus by all SCSI devices in the system to perform the data transfer between plural SCSI devices with the SCSI(Small Computer System Interface) bus. CONSTITUTION:It is asked b polling whether or not the SCSI device 1 with the highest priority needs to use the bus for other SCSI devices 2-N with the low priority, and when the reply that the bus is used is returned, the using right of the bus is given to the SCSI device, and when the use of the bus is completed, it is informed to the SCSI device with the highest priority that the use of the bus is completed, and the SCSI device with the highest priority is polled to the next SCSI device.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to SCS by polling.
The present invention relates to an I bus priority order avoidance method, and more particularly to a SCSI bus priority order avoidance method by polling that enables efficient bus communication between computers.

[0002]

2. Description of the Related Art Recently, SCSI (Small Computer System I) has been used for data transfer between a computer and its peripheral devices.
nterface) is often used. A maximum of eight SCSI devices can be connected to the SCSI bus, and each SCSI device has an ID number (ID = 0 to ID).
= 7) is attached, but the larger the ID number, the SCS
The I bus can be used preferentially. Figure 2 shows a conventional SC
FIG. 3 is a diagram showing a SI bus priority use method, and particularly FIG.
And FIG. 2B is a diagram showing a bus use procedure when data is transferred between, for example, three SCSI devices. In the figure, 1 is a SCSI device whose ID number is ID = 7, 2
Is a SCSI device whose ID number is ID = 0, 3 is a SCSI device whose ID number is ID = 1, 4 is a SCSI device 1 to SCS
It is a SCSI bus for connecting the I-device 3.

Next, a bus use procedure in data transfer between SCSI devices having the above configuration will be described. First,
As shown in FIG. 2A, the SCSI device 1 with ID = 7 and the SCSI device 3 with ID = 1 simultaneously use the SCSI device with ID = 0.
When an attempt is made to transfer data to the device 2, the SCSI device 1 with ID = 7 is given the right to use the SCSI bus 4 due to the priority order, and as shown in FIG. 2B, the SCSI device 2 with ID = 0. Data can be transferred to.

[0004]

The above-mentioned conventional SCS.
In the worst case of the I-bus priority use method, when the SCSI device with ID = 7, which has the highest priority, participates in arbitration (acquires the right to use the bus), the priority is highest. In order to obtain the right, the SCSI device having a lower priority cannot obtain the right to use the SCSI bus, and the data cannot be transferred.

[0005]

The SCSI bus priority avoidance method by polling according to the present invention does not participate in arbitration except for the SCSI device having the highest priority, and the SCSI device having the highest priority is By polling a low priority SCSI device as to whether the bus needs to be used, if the bus needs to be used, only the SCSI device gets the right to use the bus by not participating in arbitration. Then, the data is transferred.

[0006]

According to the present invention, the SCSI device having the highest priority does not occupy the bus exclusively, and a fair bus use right can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an SCS by polling according to the present invention.
It is a figure which shows one Example of the I bus priority avoidance system, and especially FIG.1 (a) -FIG.1 (e) is a figure which shows the bus use procedure at the time of transferring data between three SCSI devices, for example. is there. First, as shown in FIG. 1A, the SCSI device 1 with ID = 7, which has the highest priority, performs arbitration, and inquires the SCSI device 2 with ID = 0 whether or not it is necessary to use the SCSI bus 4. .. And ID = 0
If the SCSI device 2 returns a reply that it does not need to use the SCSI bus 4, then the ID as shown in FIG.
= 7 SCSI device 1 polls S with ID = 1
Contact the CSI device 3. Again, this ID = 1
If the reply is that the SCSI device 3 does not need to use the SCSI bus, the SCSI device 1 with ID = 7 can use the SCSI bus 4 if necessary. Also,
If the SCSI device 1 with ID = 7 does not need to use the SCSI bus 4, the SCSI device with ID = 0 again as shown in FIG.
Go to the SI device 2 for inquiry.

If the SCSI device 2 with ID = 0 is SCS
It is necessary to use the I bus 4, and the SCSI device 1 with ID = 7
When a reply indicating that the SCSI bus 4 needs to be used is returned to, the SCSI device 2 having ID = 0 performs arbitration to obtain the right to use the SCSI bus 4,
As shown in FIG. 1D, the data is transmitted to the SCSI device 3 with ID = 1. Then, when the SCSI device 2 with ID = 0 finishes using the SCSI bus 4, the SCSI device 2 with ID = 0
Notify I-device 1 that the use of SCSI bus 4 is complete. Therefore, the SCSI device 7 of ID = 7 is polled by the next SCS of ID = 1 as shown in FIG.
Contact the I-device 3. In this way, polling can be used to inquire about the use of the SCSI bus. In the above description, the case where three SCSI devices are connected has been described, but the present invention is not limited to this, and it is needless to say that the same can be achieved when four or more devices are connected.

[0009]

As described above in detail, according to the SCSI bus priority avoidance method by polling according to the present invention, priority is given to the highest priority SCSI device by controlling the bus use order. Highest SCS
There is an effect that all SCSI devices can use the bus fairly without the I device dedicating the bus.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a SCSI bus priority avoidance method by polling according to the present invention.

FIG. 2 is a diagram showing a conventional SCSI bus priority use system.

[Explanation of symbols]

 1 SCSI device with ID = 7 2 SCSI device with ID = 0 3 SCSI device with ID = 1 4 SCSI bus

Claims (1)

What is claimed is: 1. A plurality of SCSI devices using a SCSI bus.
In the method of transferring data between devices, the SCSI device with the highest priority inquires to other low-priority SCSI devices by polling whether the bus needs to be used or not, and controls the right to use the bus. SCSI bus priority avoidance method by polling.