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What is Octal Debugging Technique mean?
On-line Debugging Tool (ODT) was used to describe several debugger programs developed for Digital Equipment Corporation (DEC) hardware. Various operating systems including OS/8, RT-11, RSX-11, and RSTS/E implemented ODT as did the firmware console of all of the LSI-11-family processors including the 11/03, 11/23/24, 11/53, 11/73, and 11/83/84.
The debugger allowed access to memory using octal addresses and data. Within the software systems, the debugger accessed the process's address space. DEC's line of PDP-11 processors did not implement virtual memory, from an operating system perspective, but instead worked in a fixed address space, which was mapped into a unified view of the program's address space, using an Active Page Register (APR). An APR could map the program's RAM in increments of 4K 16-bit words, to a maximum of 32K. In other words, an APR could map 8 segments of RAM, each limited to 4K. Because of this structure, the maximum RAM an APR was able to map was 32K 16-bit words. In the case of RSTS/E, this usually meant that a Runtime System, or RTS, mapped to the upper portion of the address space and a user program resided in the lower portion of the address space. The RTS provided code to support access to the Operating System, on behalf of the user program; the RTS itself stored any of its non-static data in the address space of the user program, because the RTS was typically read-only. The operating system loaded a single copy of the RTS and this was mapped to any user program that required that RTS. The APR would be set to map the RTS into the upper portion of the program's address space, in 4K increments. So the BASIC Plus RTS (for the Basic+ Programming Language) typically mapped 16K to itself and the user program was mapped, in 4K increments, in the lower 16K. The RT11 RTS occupied 4K so a user program, like the RT11-based Peripheral Interchange Program (PIP), could expand to a maximum of 28K.
ODT could be used to "patch" binary modules, like an RTS, without requiring the re-compilation of the binary's source.
The firmware console implementation accessed physical memory.
ODT is a non-symbolic debugger and implements similar functionality to Advanced Debugger (adb) on Unix systems.
referencePosted on 30 Oct 2024, this text provides information on Miscellaneous in Computing related to Computing. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.
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