Software-fault detector for microprocessors

• Authors: Kozo Itano;Tetsuo Ida
• Venue: SIGSMALL '81 Proceedings of the 1981 ACM SIGSMALL symposium on Small systems and SIGMOD workshop on Small database systems
• Year: 1981

For the realization of the means to develop more reliable software for the microcomputers especially in real time environments, we design a hardware tool called “software-fault detector” which detects software faults such as misaccess to an element beyond the range of an array. The implementation of the mechanism for such address range checks is generally difficult in microprocessor environment, since internal registers are not readily visible to external logics. We introduce an “incremental” key-lock protection scheme into the fixed microcomputer architecture of the INTEL 8080 because of its popularity and simplicity. In this scheme, a “lock” is a protection code associated with the storage cell, and a “key” is associated with access capability such as address. In each memory access to a cell, a check is made whether a key matched against the lock of the addressed cell. In this paper, we present the details of the scheme and its analysis. Further, we present an actual hardware design of the software fault detector. Our design methodology is to realize a dector by the use of identical microprocessor 8080s, as an independent one-board module which could be connected to the memory bus of the host system.