JPH04276843A - Scsi bus monitor - Google Patents

Abstract

PURPOSE:To provide a SCSI bus monitor that can protect, when one of all of SCSI units connected to SCSI buses in a SCSI system fails with a BSY signal set on by the SCSI unit, all of the SCSI units from becoming unusable. CONSTITUTION:In a system where a plurality of SCSI units are connected to SCSI buses, a SCSI bus monitor is installed for monitoring SCSI buses, and the SCSI bus monitor consists of a differentiating circuit 6 and counter 7 for detecting the presence or absence of the change of a SCSI bus request signal for a predetermined period of time with a SCSI bus busy signal on, an n- specifying switch 12 for arbitrarily setting a predetermined period of time, and a flip-flop 8 and driver 9 for turning a SCSI bus reset signal when no change of request signal is made within a predetermined period of time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SCSI bus monitoring device, and more particularly to a SCSI bus monitoring device suitable for efficiently using the bus of SCSI devices connected to the SCSI bus.

0002

2. Description of the Related Art Conventionally, SCSI (Small Compute) has been used as a peripheral device interface for small computers.
er System Interface) Bus Interface (ANSI X3.131-1986)
There is. Devices that can be connected to this SCSI bus (hereinafter referred to as SCSI bus)
There are eight CSI devices in total, and each device has an identification number from 0 to 7 called an ID (Identifier). Examples of the SCSI device include a host computer including a host adapter, a SCSI disk controller, a tape controller, a floppy controller, a printer controller, a network controller, a CD-ROM controller, and the like. These SCSI devices are classified into devices that issue operation instructions (commands) (hereinafter referred to as initiators) and devices that execute instructions (commands) from the initiators (hereinafter referred to as targets).

FIG. 4 is a diagram showing an example of the configuration of a conventional SCSI system.

In FIG. 4, reference numerals 41 and 42 indicate an initiator which is a host computer including a host adapter;
Targets 3, 44, and 45 are controllers for various peripheral devices. Here, the target 43 is a hard disk controller, and the hard disk drive 46
-1 to 46-n are connected. The target 44 is a magnetic tape controller, and a magnetic tape drive 47-
1 to 47-n are connected. The target 45 is a printer controller to which printers 48-1 to 48-n are connected. In the figure, LUN is a logical device number indicating the address of a peripheral device connected under the target, and when the device interface under the target is ESDI, LUN=0 to 7. 49 is the initiator 41, 42
and SC to which targets 43, 44, and 45 are connected
It's an SI bus.

Next, the system operation shown in FIG.
An example in which the target 43 is selected will be explained.

[0006] First, the initiator 41
In order to issue an operation to the target, the right to use the SCSI bus 49 is acquired and the target 43 is selected. This selected target 43 is connected to the BSY signal (
Hereinafter, the BSY signal means an inverted signal) is turned on to indicate to the initiator 41 that it has been selected. BSY
The signal is also used to control the aforementioned acquisition of the right to use the SCSI bus 49, but normally it is used to notify other SCSI devices (initiator 42, targets 44, 45) that the SCSI bus 49 is in use. is controlled by target 43 in order to assert it. The selected target 43 is connected to the SCS with the BSY signal turned on.
Receives commands from the initiator 41 in accordance with the SCSI standard via other signal lines on the I bus 49 and executes operations (here, writing data to the hard disk drive, reading data from the hard disk drive, etc.) do. After the operation is completed, the target 43 turns off the BSY signal and all other SCSI signals to release the right to use the SCSI bus 49. When SCSI bus 49 is released,
The SCSI bus 49 can be used by other SCSI devices.

As described above, only the initiator 41 that has obtained the right to use the SCSI bus and the selected target 43 can use the SCSI bus 49, and other SCSI devices cannot use the SCSI bus.

[0008]

[Problems to be Solved by the Invention] However, in the conventional system described above, if one of the plurality of SCSI devices connected to the SCSI bus has the BSY signal turned on, some abnormality such as a program runaway occurs. If this occurs, not only will it be impossible to use the device, but the SCS
Since the I bus remains in use, all devices connected to the SCSI bus become unusable.

An object of the present invention is to solve such conventional problems, and in a SCSI system, when one of the SCSI devices connected to the SCSI bus turns on the BSY signal, the SCSI device To provide a SCSI bus monitoring device capable of preventing all SCSI devices from becoming unusable when an abnormality occurs.

0010

[Means for Solving the Problems] In order to achieve the above object, the SCSI bus monitoring device of the present invention includes a SCSI bus monitoring device that monitors the SCSI bus in a system in which a plurality of SCSI devices are connected to the SCSI bus. established,
The SCSI bus monitoring device includes a detection circuit that detects the presence or absence of a change in the SCSI bus request signal for a predetermined time while the SCSI bus busy signal is on, a setting circuit that arbitrarily sets the predetermined time, and a detection circuit that detects the predetermined time. SCS when there is no change in the above request signal within the time
The feature is that it is composed of a reset circuit that turns on the I bus reset signal.

[0011]

[Operation] In the present invention, SCSI bus busy (B
When the SCSI bus request (RE) signal is on,
Q) Detects (monitors) the presence or absence of a change in the signal (hereinafter, the REQ signal means an inverted signal) for a predetermined period of time, and
SCSI bus reset (
RST) signal (hereinafter, RST signal means an inverted signal) is automatically turned on. This can prevent all SCSI devices connected to the SCSI bus from becoming unusable.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained in detail below with reference to the drawings. FIG. 2 is a block diagram of a SCSI system to which the present invention is applied. This shows a configuration in which the SCSI bus monitoring device of the present invention is connected to a SCSI bus.

In FIG. 2, 21 and 22 are host computers including host adapters;
3, 24, and 25 are targets that are controllers for various peripheral devices, and 26 is a SCSI bus monitoring device of the present invention. Here, the target 23 is a hard disk controller, and hard disk drives 27-1 to 27-n
are connected. The target 24 is a magnetic tape controller to which magnetic tape drives 28-1 to 28-n are connected. The target 25 is a printer controller to which printers 29-1 to 29-n are connected. 31 is a SCSI bus. The system configuration in Figure 2 is S
SCSI bus monitoring device 26 connected to CSI bus 30
Other than this, the configuration is the same as the conventional SCSI system configuration shown in FIG.

In this embodiment, the SCSI bus monitoring device 26
The SCSI bus monitoring circuit 26 is connected to the SCSI bus 30.
The configuration is such that the SCSI bus monitoring device 26 is connected to the SC
While the BSY signal on the SI bus 30 is on, the presence or absence of a change in the REQ signal of the SCSI bus signal is detected for an arbitrarily set predetermined time, and when no change in the REQ signal is detected, the S
By automatically turning on the RST signal of the CSI bus signal, all SCSI devices are automatically turned on when an error occurs in an operating SCSI device.
It is possible to prevent the device from becoming unusable.

FIG. 1 shows a SCSI system according to an embodiment of the present invention.
FIG. 2 is a detailed configuration diagram of a bus monitoring device. This shows a detailed configuration example of the SCSI bus monitoring device 26 in FIG. Moreover, the time chart is shown in FIG. In FIG. 3, signals A to I correspond to A to I in FIG.

In FIG. 1, 1 and 2 are input terminals, 3 is an output terminal, 4 and 5 are receivers, 6 is a flip-flop, and N
A differentiation circuit consisting of an AND gate, 7 a counter, 8 a flip-flop, 9 a driver, 10 a pulse generator,
11 is a 1/n frequency divider, 12 is an n designation switch, 13 is a terminator power terminal, and 14 is a ground terminal.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 3.

The REQ signal D of the SCSI bus is a signal outputted from the target and requests the initiator to transfer data, and is inputted from the input terminal 1 via the receiver 4 to the differentiating circuit 6. This differentiating circuit 6 is connected to the REQ signal D.
This is to detect the failure even if a failure occurs in the SCSI device while the REQ signal D remains on.
The REQ signal E is output from the differentiating circuit 6 only when is a pulse signal.
Output. The REQ signal E is input to the load terminal of the counter 7, and the value of the counter 7 is initialized to 0 every time the REQ signal E is output. Therefore, when the input of the REQ signal D stops for a certain period of time, the count value F of the counter 7 reaches the maximum value, the timeout signal G is output from the carry-out terminal of the counter 7, and the flip-flop 8 is turned on. The output signal H of the flip-flop 8 is outputted to the output terminal 3 via the driver 9 as the RST signal I of the SCSI bus signal. Further, the BSY signal C is inputted via the receiver 5 to the reset terminals of the differentiating circuit 6, the counter 7, and the flip-flop 8. These circuits perform the SCSI bus monitoring operation only when the BSY signal C is on, and when it is off, these circuits are reset and the SCSI bus monitoring operation is not performed.

[0019] Once the flip-flop 8 is turned on, it becomes BS.
The on state is maintained until the Y signal C becomes off state.

A pulse generator 10 generates a basic clock A used in the present SCSI bus monitoring device. The 1/n frequency divider 11 generates an arbitrary time monitoring basic clock B from the basic clock A according to the value specified by the n designation switch 12. The basic clock B for time monitoring is input to the clock terminal of the counter 7, and the counter 7 is counted up by one with one input clock.

Furthermore, the power supply of the SCSI bus monitoring device described above is supplied from the SCSI bus signal terminator power terminal 13, thereby making it possible to reduce the cost and size.

In the above embodiment, the presence or absence of a change in the SCSI bus REQ signal is detected, but instead of the SCSI bus REQ signal, the SCSI bus ACK signal (here (the ACK signal means an inverted signal) may also be used.

[0023]

[Effects of the Invention] As explained above, according to the present invention,
By connecting a SCSI bus monitoring device to the SCSI bus, even if some abnormality occurs in the SCSI device while the SCSI device keeps the BSY signal on, the SC
The SI bus monitoring device detects the abnormality and sends the RST signal to S.
By outputting to the CSI bus, normally when a SCSI device detects the RST signal in any state, it turns off all SCSI bus signals, including the BSY signal.
All SCSI devices connected to the SCSI bus can be prevented from becoming unusable.

[Brief explanation of the drawing]

FIG. 1 is a detailed configuration diagram of a SCSI bus monitoring device showing one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a SCSI system to which the present invention is applied.

FIG. 3 is a time chart of FIG. 1;

FIG. 4 is a diagram showing a configuration example of a conventional SCSI system.

[Explanation of symbols]

1, 2 Input terminal 3 Output terminal 4,5 Receiver 6 Differential circuit 7 Counter 8 Flip-flop 9 Driver 10 Pulse generator 11 1/n frequency divider 12 n designation switch 13 Terminator power terminal 21, 22 Initiator 23, 24, 25 Target 26 SCSI bus monitoring device

Claims (1)

[Claims] 1. In a system in which a plurality of SCSI devices are connected to a SCSI bus, a SCSI bus monitoring device is provided that monitors the SCSI bus, and the SCSI bus monitoring device is configured to monitor the SCSI bus for a predetermined period while a SCSI bus busy signal is on. A detection circuit that detects the presence or absence of a change in the bus request signal, a setting circuit that arbitrarily sets the predetermined time, and the detection circuit turns on the SCSI bus reset signal when there is no change in the request signal within the predetermined time. 1. A SCSI bus monitoring circuit comprising a reset circuit for