JPH03292545A - Detection/recovery device for program loop - Google Patents

Abstract

PURPOSE:To detect a program infinite loop by saving a program counter at each fixed time, comparing the current value with the old value, and deciding a loop when the coincident state of the comparison continues with exclusion of lower rant m bits. CONSTITUTION:An old program counter 6 is compared with a current program counter 5 at each fixed time interval, and the coincidence of addresses is checked with exclusion of specific lower rant m bits. When the coincidence of addresses is confirmed, a loop counter 8 is counted up. Then a program loop detection signal is outputted when the counter 8 reaches the specific value. Based on this detection signal, the contents of a restart address register 10 are transferred to the counter 5 and the recovery processing is started. Thus a program infinite loop can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a program loop detection and recovery device for detecting and automatically recovering an infinite loop in a computer program.

[Conventional technology]

FIG. 3 is a diagram showing the sequential control unit of a computer. In the figure, (1) is the main memory, (2) is an instruction register that stores instructions read from the main memory (1), and (3) is a diagram showing the sequential control unit of the computer. is the instruction decoder, and (4) is the main memory (
1) is a memory address register that is accessed, and (5) is a current program counter that holds the address of the instruction to be executed.

Next, the operation will be explained. The instructions read from the main memory (1) are placed in the instruction register (2). The instruction code in the instruction register (2) is decoded and executed by the instruction decoder (3). In the case of a branch instruction, the lower three bytes of the instruction register (2) are entered into the current program counter (5) as a jump address. For other instructions, the current program counter (5) is incremented to point to the next instruction address. This current program counter (5)
The contents of are passed to the memory address register (4) and used for fetching the next instruction.

[Problem to be solved by the invention]

Conventional sequential control methods operate as described above, so if a program falls into an infinite loop, it cannot be detected and the CPU time is wasted or the system goes down. There was a problem.

Furthermore, Japanese Patent Application Laid-Open No. 1-140350 discloses a technique for detecting program runaway by monitoring the state of a program counter during program execution. It is difficult to predict the execution destination address and set the comparison value, and it cannot be achieved without putting a burden on the program.

This invention was made in view of the above points,
It is an object of the present invention to provide a program loop detection and recovery device for a sequential control computer, which can detect infinite program loops without putting a burden on the program, and can automatically recover the system.

(Means for Solving the Problems) A program loop detection and recovery device according to the present invention includes an old program counter that saves the contents of a current program counter that holds the address of an instruction to be executed at regular time intervals; a comparison detection means for comparing the contents of the current program counter and the old program counter excluding specific lower m bits at regular time intervals; a count loop for counting coincidence signals from the comparison detection means; and a count loop for counting coincidence signals from the comparison detection means; A restart address register is provided so that the held contents are loaded into the current program counter in response to a loop detection signal indicating that the value of has reached a specific value.

[Operation] In the present invention, the old program counter is compared with the current program counter at regular time intervals, and address matching is checked except for specific lower m bits. If they match, count up the loop counter, and when the loop counter reaches a certain value,
A program loop detection signal is issued, and this signal causes the contents of the restart address register to be transferred to the current program counter to start the recovery process.

(Example) Hereinafter, an example of the present invention will be explained with reference to the drawings.
In the figure, (1) is the main memory, (2) is an instruction register that stores instructions read from the main memory (1), (3) is an instruction decoder, and (4) is the main memory (
1) is a memory address register that is accessed; (5) is a current program counter that holds the address of the instruction to be executed; (6) is an old program counter that saves the contents of the current program counter at fixed time intervals; (a) is Comparing and detecting means (8) compares the current program counter and the old program counter excluding specific lower m bits, and sends out a match signal when the current value and the old value match; A loop counter that counts coincidence signals, (9) is a loop detection signal from the loop counter (8), (10)
is the recovery start address register.

Next, the operation of the embodiment will be explained according to the flowchart shown in FIG. At regular time intervals, the contents of the current program counter (5) are compared with the contents of the old program counter (6) by the comparison detection means (7), excluding specific lower m bits (steps 521 and S22).
). If the addresses do not match, the loop counter (
8) is cleared to O, and the old program counter (6) is cleared.
) is updated by the contents of the current program counter (5) (steps 523-525).

On the other hand, if the addresses match, the loop counter (8
) is incremented. When an infinite program loop occurs, the address of the loop is usually limited to a small area of memory space, and the lower m bits of the program address change, but the remaining upper bits remain unchanged.

Therefore, matching of addresses is detected continuously, and the count of the loop counter (8) increases continuously. and when a certain value is reached (e.g. counter overflow)
Then, the loop counter (8) outputs a loop detection signal (9) (steps s23° S26-528). This loop detection signal (9) activates the restart recovery process by transferring the contents of the restart address register (step 0) to the current program counter (5).

In the above embodiment, the address comparison detection means (7)
Although the loop counter (8) is shown as being constructed using hardware, equivalent control may be performed using microprogram control.

In addition, in the above embodiment, the old program counter (6
) shows an example of saving only the program address, but in the case of a computer with a multiple virtual memory system, the operating system should perform the processing in the flowchart in Figure 2, including the address space identifier, for each timer interrupt. For example, loops in the user program for each address space can be detected.

Further, in the above embodiment, a recovery start address register (10) is provided, but in the case of a microcomputer system, the start address register (10) may be used to start the car from address O.

Further, in the above embodiment, the case of a sequential control unit of a central processing unit of a computer was explained, but it may also be a microprogram control unit of an input/output control device or a channel control device, and the same effects as in the above embodiment can be obtained. play.

〔Effect of the invention〕

As described above, according to the present invention, the program counter is saved at regular intervals, the current value and the old value are compared, and if they continue to match except for the lower m bits, a loop is determined. As a result, it is possible to detect an infinite loop in a program, and also to break the loop and perform recovery processing.
Consumption of Pu time can be prevented, and system down and computer equipment can be automatically recovered.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a sequential control section of a computer according to an embodiment of the present invention, FIG. 2 is a flowchart showing a program loop detection method of the present invention, and FIG. 3 is a diagram showing a sequential control section of a conventional computer. FIG. (5) is the current program counter, (6) is the old program counter, (7) is the comparison detection means, (8)
is the loop counter, (9) is the loop pressure detection signal, (1
0) Beam start address register. In the figures, middle symbols indicate the same or equivalent parts.

Claims (1)

[Claims] It includes an old program counter that saves the contents of the current program counter that holds the address of the instruction to be executed at regular time intervals, and also saves the contents of the current program counter and the old program counter at regular time intervals to a specific lower order m. The current program counter is controlled by a comparison detection means for comparing bits excluding bits, a count loop for counting coincidence signals from the comparison detection means, and a loop detection signal indicating that the value of the loop counter has reached a specific value. A program loop detection and recovery device comprising: a restart address register for loading retained contents into a program loop detection/recovery device.