JPS6186848A - Detection method for microcomputer runaway - Google Patents

Abstract

PURPOSE:To detect the runaway of a program in a real time by applying a D/A conversion to the contents of a program counter and monitoring the analog voltage. CONSTITUTION:An instruction is usually executed while the contents of a program counter 2 are increased successively. Thus the 2-bit digital digital values are supplied to the input of a D/A converter 4 in the order of 00 01 10 11-, and the output of the converter 4 is changed in the expected value. While the contents of the counter 2 are rewritten to the unexpected value when a microcomputer 1 has a runaway. Therefore the analog voltage obtained by the converter 4 through a D/A conversion is also set at an unexpected level at a time point when said runaway is produced. Thus a program runaway can be detected in real time by comparing the output of the converter 4 with an existing normal voltage waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting runaway of a microcomputer.

(Prior Art) Conventionally, as a method for detecting runaway of a microcomputer, for example, Fujitsu multiplication circuit/microcomputer family (
A watchdog timer as shown in No. 1982-4) P, 264 is known.

This is a program in which the microcomputer is programmed to reset a timer that has been blown out at regular intervals according to instructions.If the microcomputer goes out of control and the program flow becomes abnormal, the timer will be reset at regular intervals. Since the timer overflows instead of every hour, it is possible to detect that the microcomputer has gone out of control.

(Problems to be Solved by the Invention) However, with this method, the moment of runaway cannot be detected, and the operating state of the microcomputer (program flow cannot be monitored). Runaway cannot be detected until the program overflows, and its internal operations cannot be monitored even during normal operation.For this reason, it is difficult to know where in the program a runaway has occurred. However, pursuing the cause of the out-of-control behavior was largely ineffective.

By the way, in a single-chip microcomputer, in order to monitor internal operations and detect runaway operations, it is sufficient to output the contents of the program counter inside the microcomputer to the outside and monitor this, but the number of terminals is always limited. In single-chip microcomputers,
This was not possible.

(Means for Solving the Problem) Therefore, in this invention, the output of the program counter is improved, a converter is connected, and the analog voltage obtained by D/A converting the contents of the program counter is outputted from one terminal to the outside of the microcomputer. and monitor its output waveform.

(Function) During normal operation, the program counter of a microcomputer is sequentially incremented (steps), and if there is an instruction that completely changes the flow of the program, the program counter cannot be rewritten to the desired content at that point. In any case, by D/A converting the contents of the program counter, an analog voltage corresponding to the contents of the program counter can be obtained. Therefore, by monitoring this analog voltage by comparing it with a known normal voltage, it is possible to monitor the operating status of the program counter and, by extension, the internal operation of the microcomputer. can be detected.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is a microcomputer, 2 is a 1-yen program counter for the microcomputer, 3 is a read-only memory (hereinafter referred to as ROM), 4 is an analog/A converter, and 5 is a monitoring output terminal of the microcomputer l. For the sake of explanation, other components of the microcomputer I are omitted.

In order to read the instructions stored in the ROM 3, the program counter 2 has, for example, seven address outputs that have a weight of a power of 2 from the lower order, and are connected to the address inputs of each ROM 3. Two wires (two on the count start side) are also connected to the D/A converter 4. In that series, the output of converter 4 is the monitoring output terminal 5
It is connected to the. It should be noted that connecting the output from the program counter 2 to the converter 4 as described above only needs to be done to distribute digital pulses.

FIG. 2 shows a specific example of the converter 4.

As shown in this figure, the D/A connector 4 has a resistance R
1, R2 and transistors Ql, Q2.

FIG. 3 shows an example of the waveform of the monitoring output terminal 50, where CB shows an example of normal operation and CB shows an example of runaway.

The operation of FIG. 1 will be explained with reference to this waveform diagram.

Normally, when the microcomputer 1 does not execute instructions that change the program flow, such as jump instructions or call instructions, the microcomputer 1 executes all instructions while the contents of the program counter 2 are sequentially incremented. go. Therefore, 2-bit digital values are input to the input of the D/A converter 4 in the order of OO→O1→10→11→00→01... Therefore, this
When the D/A converter 4 performs D/A conversion, its output, that is, the monitoring output terminal 5, has four analog voltage levels, a+b+c+d, corresponding to the increment of the program counter 2, as shown in FIG. 3 (4). (Figure 3 shows the contents of the program color/re2, that is, the ROM
Output terminal 5 for monitoring when address 3 increments from 0 to 8
0 waveform).

Furthermore, if there is a command that changes the flow of the program, the contents of the program counter 2 are rewritten to the desired contents, so the analog voltage level corresponding to the rewritten contents is output to the monitoring output terminal 5 at that point. be done.

In contrast to such normal operation, if the microcomputer 1 goes out of control, the contents of the program counter 2 will be overwritten at that point and become an unexpected value. Therefore, the analog voltage obtained by D//A conversion of the contents of the program counter 2 by the converter 4 also reaches an unexpected level at the time of runaway. For example, microcomputer l operates normally up to address 2, but when it executes all instructions at address 3, it goes out of control and returns to address 0. After executing again up to address 2, it runs out of control at address 3 and returns to address 0. , if this is repeated every time, as shown in Figure 3 (8), the point where the analog voltage level originally rises to the d level (corresponding to address 3) after the C level (corresponding to address 2) is C. It repeatedly goes down to the level (corresponding to address 0), rises to the C level again, and then falls back to the C level when it reaches the d level.

Therefore, by monitoring the voltage waveform of the monitoring output terminal 5 from which the analog voltage is output by comparing it with a known normal voltage waveform, the internal operating state of the microcomputer 1 can be monitored, and if a runaway occurs, this can be implemented. Can be detected by time.

In the above embodiment, the input of the goods A converter 4 is 2.
The more input you have, the better the monitoring accuracy will be. However, from a cost standpoint, three to four wires are practical. Furthermore, although the explanation has been made on the premise that the input to the converter 4 has a weight of a power of 2, this is not restrictive.

(Effects of the Invention) As described above, according to the method of the present invention, a D/A converter is connected to the output of the program counter inside the microcomputer, and the output of the D/A converter is taken out to the outside of the microcomputer. Since it is monitored, the internal operation of the microcomputer can be monitored, and if it goes out of control, it can be detected in real time. Further, according to this method, the monitoring signal (D/A converter output) can be outputted to the outside of the microcomputer from one terminal, and therefore it is particularly suitable for single-chip microcomputers where the number of terminals is always limited. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining one embodiment of the microcomputer runaway detection method of the present invention, FIG. 2 is a specific circuit diagram of the converter shown in FIG. FIG. 3 is a waveform diagram for explaining the operation of an example. l...Microcomputer, 2...Program counter, 3...ROM, 4..."/A converter,
5...Output terminal for monitoring. Figure 1 Figure 2 Shi-,-,,j Figure 3

Claims (1)

[Claims] A runaway detection method for a microcomputer, which comprises connecting a D/A converter to the output of a program counter inside the microcomputer, and taking out the output of the D/A converter from one terminal to the outside of the microcomputer for monitoring.