US 5,701,492 A · Fail-safe flashing of EPROM

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.

Claims14

Dependent claims

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.

6 more elements

Dependencies are inferred from the claim text.

Fail-safe flashing of EPROM

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Fail-safe flashing of EPROM

Life of this patent

Abstract

Claims14