JPH0535538A - Micro Processor - Google Patents

Abstract

(57) [Summary] [Object] The present invention is characterized in that runaway detection can be immediately performed in all instruction processing including branch instructions and interrupt instructions without depending on firmware. [Structure] Each time a subroutine call is made, a counter 11 is incremented, pushed onto a stack, and the counter value that is popped at the time of return is compared with the counter value at that time by a comparator 12, and if they are different, a runaway It is characterized by having a hardware capable of detecting runaway of a program immediately upon return from a subroutine jump.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microprocessor incorporating a program runaway detection circuit.

[0002]

2. Description of the Related Art In recent years, advances in semiconductor technology have made it possible to supply microprocessors, peripheral control LSIs, and memory LSIs at a very low cost. Now you can build.

In particular, the performance of the microprocessor, which is the control center of this kind of personal computer, has been remarkably improved, and not only 8-bit, 16-bit and 32-bit data processing but also 64-bit processing or those with a built-in cache have recently appeared. I've been

By the way, the above-mentioned personal computer stores a program in a built-in memory, and executes data processing while reading the content according to an address set in a program counter. The program counter indicates the memory address of the next instruction to be executed,
It is updated every time the instruction is executed and the next address is set. In such a system, in order to detect a program runaway during normal data processing, conventionally, for example,
Depending on the firmware, such as a watchdog timer, an instruction to reset the timer is included in the program, and when the value of the program counter exceeds a certain set value, it is judged as a runaway and the runaway is detected.

[0005]

Conventionally, since the runaway is detected by counting up the timer to show a certain value, the runaway cannot be detected immediately. In any case, the program had to be modified, which puts a heavy burden on the programmer. In order to solve this problem, it is conceivable that the microprocessor has a circuit for inspecting the value of the program counter by a compare and that detects the runaway immediately without depending on the firmware. However, even if the instructions stored in the memory are executed sequentially, a means for prohibiting the compare operation at the time of processing a branch instruction or an interrupt instruction is necessary, and therefore a runaway cannot be detected and a runaway occurs at that time. However, it was not detectable.

It is an object of the present invention to provide a microprocessor which can detect runaway immediately in all instruction processing including branch instructions and interrupt instructions without depending on firmware.

[0007]

[Constitution of the invention]

[0008]

A microprocessor of the present invention includes a decode circuit for decoding instructions, a counter for updating n-bit data by detecting a subroutine call or a return instruction by the decode circuit, and a subroutine call. A stack control circuit that updates the counter each time and pushes it to the storage device and pops the value at each return, and a comparison circuit that compares the popped value and the counter value at that time The feature is that a program runaway is detected based on a comparison result by a circuit.

[0009]

With the above-mentioned configuration, the counter is incremented for each subroutine call and pushed on the stack.
The value of the counter popped at the time of return is compared with the counter value at that time, and if they are different, it is considered as a runaway. By implementing all of these processes by hardware without using firmware, it is possible to immediately detect runaway of a program when returning from a subroutine jump.

[0010]

1 is a block diagram showing an example of the configuration of a personal computer in which the present invention is used.

In the figure, 1 is a microprocessor (μ
It is a CPU) and reads a program stored in the system RAM 2 or a program stored in the BIOS-ROM 3 (basic input / output system) to perform arithmetic control or control of each input / output device connected to the system. A stack area used in the present invention is allocated to the system RAM 2 in addition to the program area.

Reference numerals 4, 5 and 6 are input / output devices,
Reference numeral 4 is a keyboard (KB) for inputting data, 5 is a floppy disk device (FDD) serving as an external storage, and 6 is a display device (CRT) for displaying data. All of these input / output devices are controlled by a BIOS program, and all of them are keyboard controller (KBC) 7, floppy disk controller (FDC) 8, display controller (CRT) which are input / output controllers programmable by the microprocessor 1.
C) Connected via 9.

FIG. 2 is a block diagram showing an embodiment of the present invention, and shows only a portion of the microprocessor 1 shown in FIG. 1 which is relevant to the present invention.

In the figure, reference numeral 11 is a counter, which raises / downs n-bit data by detecting a branch instruction. Reference numeral 12 is a comparison circuit, which compares the value of the counter 11 described above with the value read from a storage device (stack mechanism) not shown. Reference numeral 13 is a selector, which switches the value of the counter 11 and the value obtained from the stack mechanism and supplies the value to the comparison circuit 12.

The operation of the embodiment of the present invention will be described below.

As described above, the present invention counts up the counter for each subroutine call and pushes it on the stack. The value of the counter popped on return is compared with the counter value at that time, and if they are different, it is considered as a runaway. The above processing functions are not dependent on the firmware,
By implementing all in hardware, it is possible to immediately detect runaway programs when returning from a subroutine jump. For this purpose, an instruction decoding circuit for detecting a subroutine call, a return instruction, etc. is provided.

The operation of the embodiment of the present invention will be described below with reference to FIG.

First, when the subroutine call instruction is executed, the value of the counter 11 is updated (up-counted) and pushed to the storage device (stack).

The same operation is repeated when the branch instruction is repeated.

Next, when returning to the branch point from the branch destination by the return instruction, the value is popped from the above-mentioned memory device, and the counter 1 is counted by the comparison circuit 12 via the selector 13.
Compared with 1 value, if data disagreement is shown, it is judged as a runaway.

If the data match, it is determined that the operation is normal, the counter 11 is down-counted, and the process proceeds to the next instruction processing.

The same operation is repeated when the return instruction is repeated.

Depending on the output of the comparison circuit 12, the runaway can be avoided by stopping the operation of the microprocessor for avoiding the program runaway or adding a circuit for forcibly returning to the initial routine.

[0024]

As described above, according to the present invention, runaway of a program can be immediately detected in all instruction processing including branch instructions, and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a personal computer to which the present invention is applied.

FIG. 2 is a block diagram showing an embodiment of the present invention.

[Explanation of symbols]

 11 ... Counter, 12 ... Comparison circuit, 13 ... Selector.

Claims (1)

Claim: What is claimed is: 1. A decoding circuit for decoding an instruction, a counter for updating n-bit data by detecting a subroutine call or a return instruction by this decoding circuit, and a counter for each detection of the subroutine call. The comparison circuit includes a stack control circuit that updates the counter and pushes it to a storage device, and pops the value at each return, and a comparison circuit that compares the popped value with the counter value at that time. A microprocessor characterized by detecting a program runaway according to the result of comparison.