Fail-safe flashing of EPROM

• US 5,701,492 A
• Filed: 03/29/1996
• Issued: 12/23/1997
• Est. Priority Date: 03/29/1996
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Danknick, Daniel A., Wadsworth, Robert D.
• Primary Examiner(s): Kriess, Kevin A.
• Application Number:
  US08/625,033
• Time in Patent Office: 634 Days
• Field of Search: 395/651, 395/652, 395/653, 395/712, 395/430, 395/479, 395/483, 395/490, 395/750
• US Class Current: 717/173
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 8/65 Updates security arrangements therefor G06F21/57
• CPC Class Codes: G11C 29/765 in solid state disks

Abstract

A fail-safe flash for an EPROM that is arranged into separately erasable sectors proceeds in a stepwise procedure. The EPROM is divided into at least three regions including a boot block region, a file region and a directory region. The boot block region stores at least two independently erasable boot blocks, only one of which is designated as a current boot block, which performs scanning of the directory region so as to determine a current directory in the directory region. The file region stores all executables, including executables designated as critical and non-critical. The directory region stores multiple directories, only one of which is a current directory, which designates which is the current boot block, which of the files stored in the file region are available for loading for execution, as well as which of the files are critical and which are non-critical. In the first step to flash the EPROM, the unused region of the boot block is updated with the new boot block. In the second step of flashing the EPROM, critical files are flashed over non-critical files, and after correct installation of the newly-flashed critical files is confirmed, a new directory is written into the directory region referring only to the newly-flashed critical files. In the third step of flashing the EPROM, non-critical files are flashed, whereafter a new directory is written to the directory region referring to the newly-flashed critical files as well as to the newly-flashed non-critical files.

Claims

1. A flashable embedded device comprising:

a flashable EPROM arranged into separately erasable sectors, the EPROM being divided into at least three regions including a boot block region, a file region and a directory region;

wherein said file region has stored therein plural executable files of program instruction sequences;

wherein said directory region has stored therein at least two directories including a current directory, each of the directories having a boot block select field and file entries which identify at least some of the files stored in said file region; and

wherein said boot block region has stored therein at least two boot blocks, one of which begins at a predesignated address, and which contains process steps which scan said directory region to identify the current directory, and to identify the boot block select field of the current directory;

said flashable embedded device further including a DRAM into which executable program instruction sequences may be copied from said EPROM; and

a microprocessor for executing program instruction sequences commencing at power application from the predesignated address in said EPROM;

wherein upon power application, said microprocessor commences execution of program instruction steps at the predesignated address of said EPROM so as to scan said directory region to determine the current directory, to select one boot block from said boot block region based on the boot block select field of the current directory, to complete execution of the selected boot block whereby at least some files stored in said file region and listed in the current directory of said directory region are transferred to said DRAM, and to commence execution of said files stored in DRAM.

2. A flashable embedded device according to claim 1, wherein files in said file region include a safe flash agent which is adapted to communicate with a safe flash client located remotely of said embedded device.

3. A flashable embedded device according to claim 2, wherein files in said file region are designated as critical or non-critical, and wherein said safe flash agent is adapted to respond to commands from said safe flash client so as to flash new versions of critical files into said EPROM and to confirm correct installation thereof before flashing new versions of non-critical files into said EPROM.

4. A flashable embedded device according to claim 2, wherein said safe flash agent is adapted to write a new directory into said directory region, and to designate the newly-written directory as a current directory, after critical files have been written.

5. A flashable embedded device according to claim 4, wherein said safe flash agent is adapted to write a new directory into said directory region, and to designate the newly-written directory as a current directory, after non-critical files have been written.

6. A method for flashing flashable EPROM that is arranged into separately erasable sectors and which is divided into at least three regions including a boot block region, a file region, and a directory region, the method comprising the steps of:

a boot block flash step in which an unused region of said boot block region is updated with a new boot block;

a critical file flash step in which critical files in said file region are flashed over non-critical files, and in which a new directory is written into said directory region after successfully flashing critical files; and

a non-critical file flashing step in which non-critical files are flashed into said file region, and in which a new directory is written into said directory region after successfully flashing non-critical files.

7. A method according to claim 6, wherein in said boot block flashing step, at least one sector of said EPROM is not erased.

8. A method according to claim 6, further comprising a step of storing a copy of a current directory from said directory region into DRAM for use during said critical file flashing step and said non-critical file flashing step.

9. A method according to claim 8, wherein said critical file flashing step is produced by the step of deleting, from the DRAM copy of a current directory, non-critical files, and flashing said directory region with the DRAM copy of the directory region.

10. A method according to claim 9, wherein said critical file updating step further includes the step of deleting critical files from the DRAM copy of the current directory, and adding newly-flashed critical files to the DRAM copy of the current directory.

11. A method according to claim 10, further comprising the step of flashing the DRAM copy of the directory to said directory region of the EPROM.

12. A method according to claim 8, wherein said non-critical file flashing step includes the step of adding newly-flashed non-critical files to the DRAM copy of the current directory, and flashing the DRAM copy of the directory to said directory region of the EPROM.

13. Computer executable process steps stored on a computer-readable medium, said steps for flashing flashable EPROM that is arranged into separately erasable sectors and which is divided into at least three regions including a boot block region, a file region, and a directory region, said steps comprising:

a boot block flash step in which an unused region of said boot block region is updated with a new boot block;

a critical file flash step in which critical files in said file region are flashed over non-critical files, and in which a new directory is written into said directory region after successfully flashing critical files; and

a non-critical file flashing step in which non-critical files are flashed into said file region, and in which a new directory is written into said directory region after successfully flashing non-critical files.

14. An apparatus for flashing flashable EPROM that is arranged into separately erasable sectors and which is divided into at least three regions including a boot block region, a file region, and a directory region, said apparatus comprising:

a memory including a region for storing executable process steps and including a region for storing a new boot block, new critical files, and new non-critical files; and

a processor for executing the process steps stored in said memory;

wherein the process steps include (i) a boot block flash step in which an unused region or said boot block region is updated with a new boot block, (ii) a critical file flash step in which critical files in said file region are flashed over non-critical files, and in which a new directory is written into said directory region after successfully flashing critical files, and (iii) a non-critical file flashing step in which non-critical files are flashed into said file region, and in which a new directory is written into said directory region after successfully flashing non-critical files.