JPH11167525A - Nonvolatile-memory mixedly mounted microcomputer and nonvolatile memory rewriting method thereof, and recording medium where nonvolatile memory rewriting program of nonvolatile-memory mixedly mounted microcomputer is recorded - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the nonvolatile memory rewriting method of the nonvolatile-memory mixedly mounted microcomputer which easily perform rewriting operation characteristic of a user without letting a third person illegally know the program by introducing a password which is difficult to predict. SOLUTION: This nonvolatile-memory mixedly mounted microcomputer 1 is equipped with a BOOT program which performs a predetermined process. In this case, when a control program unique to a user is transferred from outside by executing the BOOT program, the matching of a password is requested. A third person who does not know the password is disabled to transfer a desired control program from outside, and consequently the nonvolatile memory 7 is prevented from illegally being read out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a one-chip microcomputer in which a nonvolatile memory is embedded, and more particularly to a method of rewriting a program stored in the nonvolatile memory.

[0002]

2. Description of the Related Art Microcomputers have become highly integrated, high-performance, and highly functional with the development of LSI technology. Today, not only information processing products such as personal computers and workstations, but also home appliances, automobiles, Used in all industrial and consumer products. Among them, a one-chip microcomputer having a memory and an input / output control function on the same chip is suitable for a small-scale product, and further development is expected in the future.

In recent years, nonvolatile memories, especially flash memories (flags) have been added to the one-chip microcomputers.
Microcomputers with embedded non-volatile memory embedded with sh memory) have been widely used. Generally, a non-volatile memory is
An LSI memory that can electrically rewrite data freely and retain data even when the power is turned off.In particular, flash memory has the potential to replace magnetic disks with high density and high integration. It is also a highly promising memory.

The one-chip microcomputer in which the electrically rewritable and erasable flash memory is mounted, as described above, is mounted on home appliances, automobiles and the like, and controls them. Is written into the non-volatile memory.

Here, the control program written in the nonvolatile memory does not always operate normally from the beginning. For example, a bug may be found after being written. In such a case, it is necessary to rewrite the control program written in the nonvolatile memory to a normal one. In addition, it is necessary to check whether the written control program is normal or to verify the contents of the nonvolatile memory to debug the program for development purposes, etc., and in some cases, it may be necessary to rewrite it. . Furthermore, in recent navigation systems, there is also a situation in which a new program is read using, for example, a CD-ROM or a memory card, thereby rewriting the program written in the nonvolatile memory and performing a version upgrade.

[0006] In some cases, the program once written in the nonvolatile memory must be rewritten. At this time, an important matter is prevention of leakage of the program stored in the nonvolatile memory. In other words, the fact that rewriting is possible may cause a third party to illegally read the contents. Usually, such program rewriting is performed by using a prepared program (here, BOOT
(Called a (boot) program). In other words, the conventional microcomputer with embedded nonvolatile memory,
A BOOT program for performing a plurality of predetermined processes is provided in advance, and one of the processes is a data rewriting operation of the nonvolatile memory. Such a BOOT program will be
This mode is executed when a mode is set, and is normally stored in a ROM (usually a mask ROM is used) which is a read-only memory, so that no change is possible.
There is also a case where a fixed area of the non-volatile memory is secured as a BOOT program storage area and stored there.

When actually rewriting a program in a nonvolatile memory using the BOOT program, first,
When the BOOT mode is set, the BOOT program starts, and when a predetermined command requesting rewriting of the non-volatile memory is input, the BOOT program is executed and rewriting of the non-volatile memory is performed. . Here, if the above operation is performed by a third party, there is a risk that the control program stored in the non-volatile memory may be read. For this reason, in the rewriting operation, the BOOT program is designed so that the program stored in the nonvolatile memory is temporarily erased before writing a new program. Therefore, by making it impossible to rewrite the program stored in the non-volatile memory except for the execution of the BOOT program,
It is possible to prevent a third party from knowing the contents of the program stored illegally.

[0008]

However, the rewriting operation of the non-volatile memory may not be able to sufficiently satisfy the user's request by the method using the above-described BOOT program, and another rewriting method that meets the user's request may be used. It is often necessary to equip it. Therefore, in practice, the user can transmit a non-volatile memory rewriting program prepared by the user from the outside and execute the program to perform a user-specific rewriting operation. Specifically, as described above, BOOT
When the mode is set, the BOOT program is started. Next, when a predetermined command is input, the BOOT program is executed and the program prepared by the user is loaded into the built-in RAM. Then, by executing the user's program, the rewriting operation as requested by the user is performed.

However, this makes it possible for a third party to perform the required work. That is, if a program for reading a program stored in the nonvolatile memory is loaded and executed in the same manner as described above, a third party can easily and illegally know the contents of the stored program. Because.

Accordingly, the present invention has been made in view of the above circumstances, and has as its object to introduce a password which is difficult to predict, thereby preventing a third party from illegally knowing the program and making the program unique to the user. The present invention is to provide a microcomputer with a built-in nonvolatile memory and a method for rewriting the nonvolatile memory, which can easily perform the rewriting operation of the nonvolatile memory.

[0011]

In order to achieve the above object, the present invention provides a CPU 3 for performing various controls, a RAM 5 that can be read and written at any time, and an external controller 11.
Peripheral I / O 13 interfacing with the CPU, a non-volatile memory (flash memory) 7 for storing a program to be executed by the CPU 3, and a BOOT for performing a predetermined process.
In a general nonvolatile memory-equipped microcomputer 1 including a program, a user-specific nonvolatile memory rewriting program is transferred from the external controller 11 to the RAM 5 via the peripheral I / O 13 by executing the BOOT program. When rewriting the non-volatile memory 7 by executing the non-volatile memory rewriting program, by requesting a password match before the transfer, a third party who does not know the password can use a unique program such as the non-volatile memory. It is intended to prevent the illegal reading of the program in the nonvolatile memory by transferring the read program and executing the read program.

Further, in the present invention, since the data of the program written in the nonvolatile memory is used as the password, it is more difficult to match the passwords. Specifically, the number of passwords,
The content of the password is determined from the data stored at the first address (address for storing the number of passwords) which is an arbitrary address of the nonvolatile memory 7 and the content of the password is determined.
The password is determined from the data stored in each of the addresses consecutive by the number of passwords including the second address (password comparison start address) which is an arbitrary address and the password comparison start address. The password number storage destination address and the password comparison start address are arbitrary, and can be independently determined by the user according to security needs.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

First, the configuration of a general nonvolatile memory mixed microcomputer will be described. FIG. 1 is a diagram showing a configuration of a general microcomputer with embedded nonvolatile memory. As shown in FIG.
Is a CPU (central processing unit) 3
A readable / writable RAM (rand) that temporarily holds various programs transferred from the external controller
om access memory) 5, a nonvolatile memory (flash memory) 7 for storing a control program for the microcomputer 1,
Read-only ROM for storing OT programs (read only
memory) 9, a peripheral I / O 13 that performs a serial interface with the external controller 11, and a data bus 15 that exchanges various data.

Further, as described in the prior art, when a certain area of the nonvolatile memory 7 is secured as a BOOT program storage area and the BOOT program is stored therein,
The ROM 9 becomes unnecessary. Here, a case where the BOOT program is stored in the ROM 9 will be described.

As described in the related art, the microcomputer 1 with the nonvolatile memory having the above-described configuration is mounted on a home appliance, a car, or the like, and controls them by a control program stored in the flash memory 7. Is what you do.

When the control program stored in the flash memory 7 needs to be rewritten, the BOOT program stored in advance in the ROM 9 is started, and the flash 7
Are erased collectively. Thereafter, a new control program transmitted from the external controller 11 is transferred to the flash memory 7 via the peripheral I / O 13,
As a result, data rewriting of the flash memory 7 is executed.

Next, a method of rewriting the nonvolatile memory by executing a program for rewriting the nonvolatile memory 7, which is a user program prepared by the user, according to the present embodiment will be described.

In the prior art, when user-specific control, for example, rewriting of the non-volatile memory 7 is made possible by a user program transferred from the outside, the control can be freely performed by a third party. Therefore, there is a possibility that data in the nonvolatile memory 7 may be illegally known.

In this embodiment, the external controller 11
To transfer the user program to the RAM 5 and perform user-specific control, the password (password) before the transfer
By requesting that the password match, the transfer of the user program of a third party whose password does not match is prevented, thereby making it impossible for a third party to control the microcomputer illegally. Further, in the present embodiment, the password is created using a predetermined address of the nonvolatile memory 7 and the contents of the data stored therein, thereby attempting to control the microcomputer illegally (especially, the nonvolatile memory 7). It is possible to make it very difficult for a third party to match the password.

The setting of the password is performed, for example, as follows. FIG. 2 is a conceptual diagram of a password area in the nonvolatile memory 7 of FIG. As shown in FIG. 2, the area in which the password can be specified is usually limited to a predetermined area of the nonvolatile memory 7, and here, 10000H
The area from address to address 12000H and the area from address 2DFFFH to address 2FFFFH are excluded.
The area from address H to address 2DFFFH is defined as an area in which a password can be specified.

First, a password number storage destination address (PNSA) is set for this specifiable password area (here, referred to as a specifiable password area). The number (N) of passwords to be compared is determined based on the contents of the data stored at the address set here. For example, if the data stored in the password number storage destination address indicates 2 bytes (N = 2), 2 bytes counted from the password comparison start address (PCSA) described later
(N = 2) password comparisons are performed. Here, the password number storage destination address may be reserved in advance for storing data for determining the number of passwords, or a predetermined address of a program originally stored in the nonvolatile memory 7. Out of the data stored in the password may be selected, and the address may be used as the password number storage destination address. Further, in the above description, the number of passwords (N) is 2 bytes (pieces). However, the present invention is not limited to this, and the number of passwords may be further increased to improve security. However, it is a problem that the number is too small from the viewpoint of security, and it is desirable to set a minimum number of passwords in advance and determine the number of passwords to be larger than this number.

Second, the password comparison start address (PCS
Set A). The comparison of the passwords starts from the address set here, and the comparison is performed by the number of passwords determined by the password number storage destination address. That is, the passwords are compared in the area from (password comparison start address) to (password comparison start address + N-1), and this area becomes the password area actually specified by the user.

Next, a description will be given of a method of rewriting the nonvolatile memory using the BOOT program of the microcomputer with the nonvolatile memory according to the present embodiment. FIGS. 3 and 4 are flowcharts showing the processing procedure of the nonvolatile memory rewriting method according to the present embodiment. It is assumed that a predetermined BOOT mode has been set and the BOOT program has been activated before this process. Further, a series of processes described below are performed by executing the BOOT program.

As shown in FIG. 3, in step 1,
First, a password number storage address (PNSA) is input.

Next, in step 2, it is determined whether or not the password-number storage address input from the outside exists in a preset specifiable password area. If it is determined that the input password number storage address is not in the specifiable password area, that is, if an unauthorized third party who does not know the correct password number storage address inputs an incorrect address, The process proceeds to step 3 shown in FIG. 4, enters an infinite loop without transmitting anything to the outside, and ends as it is.

Next, if it is determined in step 2 that the password number storage destination address entered exists in the specifiable password area, in step 4
It is determined whether or not the number of passwords N determined by the contents of the data stored in the password number storage destination address is larger than a predetermined minimum number of passwords. The number of passwords N determined from the contents of the data stored at the input address of the number of input passwords storage destination
If the password is determined to be smaller than the minimum password, that is, if an unauthorized third party who does not know the correct password number storage destination address inputs an incorrect address as in step 2 above, step 3 shown in FIG. To enter an infinite loop without sending anything to the outside, and the process ends.

Next, when it is determined that the number N of passwords determined from the contents of the data stored in the password number storage destination address input in step 4 is larger than the minimum password, password comparison starts. Address (PCSA) input becomes possible. Then, in step 5, a password comparison start address is input.

Next, at step 6, it is determined whether or not the password comparison start address input from the outside exists in a preset specifiable password area. When it is determined that the input password comparison start address does not exist in the specifiable password area, that is, when an unauthorized third party who does not know the correct password comparison start address inputs an incorrect address, FIG. The process proceeds to step 3 shown in (1), enters an infinite loop without sending anything to the outside, and ends as it is.

Next, when it is determined in step 5 that the password comparison start address entered exists in the specifiable password area, the password input actually starts. More specifically, password comparisons are sequentially performed in the area from (password comparison start address) to (password comparison start address + N-1). First, in step 7, a password to be compared with the data (password) stored at the address (PCSA + n-1) is input from outside. Here, n is an arbitrary integer from 1 to N. For example, when n = 1, (PCSA + n−1) indicates the password comparison start address itself, and when n = N, (PCSA + n−1) + n-1) indicates the last address to be compared by the password number N from the password comparison start address.

Next, at step 8, it is determined whether or not the password input at step 7 matches the data (password) stored at the corresponding address. If it is determined that the input password does not match the data (password) stored at the corresponding address, that is, if an unauthorized third party who does not know the correct password inputs the incorrect password, FIG. The process proceeds to step 3 shown in (1), enters an infinite loop without sending anything to the outside, and ends as it is.

Next, when it is determined in step 8 that the input password matches the data (password) stored in the corresponding address, it is determined in step 9 whether n = N. Is done. That is, this is a step in which it is confirmed whether or not the determination of the coincidence of all the passwords is completed. Therefore, if n = N is not satisfied, all of the passwords have not yet been determined to match, so 1 is added to n and the process returns to step 7 again.
Steps 8 and 9 are executed similarly. On the other hand, n =
If the answer is N, it means that the confirmation of matching of all the passwords has been completed.

If it is determined in step 9 that the confirmation of the agreement of all the passwords has been completed, that is, if all the passwords match, in step 10, the BOOT program is executed as in the prior art from the outside to The rewriting program of the nonvolatile memory 7 to be transmitted is loaded into the RAM 5, and a specific rewriting process is executed by the loaded program.

As described above, in the present embodiment, when a user-specific control program is loaded into the built-in RAM and the user-specific processing is performed by executing the control program, the password is not loaded when the control program is loaded. It requires a match. Therefore, according to the present embodiment, when a user-specific rewriting program is loaded and the program is processed as requested by the user by executing the program, no problem occurs if the legitimate user knows the password. Instead, it is possible to load a predetermined rewriting program from the outside. On the other hand, even if a third party who does not know the password illegally reads the data in the nonvolatile memory and tries to load the reading program from the outside, the loading becomes impossible due to the password mismatch. Therefore, data in the nonvolatile memory cannot be read.

Further, in the present embodiment, an arbitrary address of the non-volatile memory and a combination of data stored at the address are used as the password, so that a third party who does not know the password is very difficult. It is difficult to predict, and it is impossible for a third party to control the microcomputer illegally.

Here, a program for realizing the above-described method for rewriting the nonvolatile memory can be stored in a computer-readable recording medium. The recording medium can be read by a computer system, and the above-mentioned rewriting method can be realized while controlling the computer by executing the program. Examples of the recording medium include devices capable of recording a program, such as a memory device, a magnetic disk device, and an optical disk device.

[0037]

As described above, according to the present invention,
When performing unique control by executing a user program transferred from outside, password (pas
Requesting the matching of the sword) prevents the transfer of the user program of the third party whose password does not match, thereby preventing the third party from illegally controlling the microcomputer.

Further, according to the present invention, it is possible to illegally read the contents of the nonvolatile memory by creating the password using an arbitrary address of the nonvolatile memory and the contents of data stored therein. This makes it very difficult for a third party to match the password.

According to the present invention, the burden on the user for security can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a general microcomputer with embedded nonvolatile memory.

FIG. 2 is a conceptual diagram of a password area in the nonvolatile memory 7 of FIG.

FIG. 3 is a flowchart showing a processing procedure of a nonvolatile memory rewriting method according to the present embodiment (part 1).

FIG. 4 is a flowchart showing a processing procedure of a nonvolatile memory rewriting method according to the present embodiment (part 2).

[Explanation of symbols]

 1 Microcomputer with embedded nonvolatile memory 3 CPU 5 RAM 7 Nonvolatile memory (flash memory) 9 ROM 11 External controller 13 Peripheral I / O 15 Data bus

Claims (6)

[Claims] 1. A CPU that performs various controls, a RAM that can be read and written at any time, and a peripheral I / O that interfaces with an external controller
A nonvolatile memory that stores a program to be executed by the CPU; and a nonvolatile memory mixed microcomputer that includes a BOOT program for performing a predetermined process. After rewriting the non-volatile memory by executing the non-volatile memory rewriting program after transferring the non-volatile memory rewriting program to the RAM, requesting a password match before the transfer is performed. Memory embedded microcomputer. 2. The number of passwords is determined from data stored at a first address which is an arbitrary address of the nonvolatile memory, and the content of the password is determined by an arbitrary address of the nonvolatile memory. 2. The microcomputer with embedded nonvolatile memory according to claim 1, wherein the data is stored in a second address which is an address and in addresses including the second address, the addresses being continuous by the number of passwords. 3. A boot program for performing a predetermined process is provided, and after executing the boot program, a nonvolatile memory rewriting program is externally transferred,
A non-volatile memory rewriting method for a non-volatile memory embedded microcomputer that rewrites the non-volatile memory by executing the non-volatile memory rewriting program, wherein a password match is required before the transfer. Rewriting method of nonvolatile memory of embedded microcomputer. 4. The number of passwords is determined from data stored at a first address which is an arbitrary address of the nonvolatile memory, and the content of the password is determined by an arbitrary address of the nonvolatile memory. 4. The nonvolatile memory according to claim 3, wherein the data is stored in a second address that is an address, and data that is stored in each of the addresses that are consecutive by the number of passwords including the second address. Memory rewriting method. 5. A nonvolatile memory rewriting program is externally transferred by executing a BOOT program for performing a predetermined process, and then the nonvolatile memory is rewritten by executing the nonvolatile memory rewriting program. A recording medium on which a nonvolatile memory rewriting program of a microcomputer with embedded nonvolatile memory is recorded, wherein a password match is requested before the transfer. Medium. 6. The number of passwords is determined from data stored at a first address which is an arbitrary address of the nonvolatile memory, and the content of the password is determined by an arbitrary address of the nonvolatile memory. 6. The non-volatile memory according to claim 5, wherein the data is stored in a second address that is an address, and data that is stored in each of the addresses that are consecutive by the number of passwords including the second address. A recording medium on which a memory rewriting program is recorded.