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On-line Debugging Tool

  (Redirected from Octal Debugging Technique)

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 virtual memory. The firmware console implementation accessed physical memory.

ODT is a non-symbolic debugger and implements similar functionality to Advanced Debugger (adb) on Unix systems.


Console ODTEdit

Console ODT[1] replaced the lights and switches console of many of the earlier processors.

Access to console ODT is obtained either from power up (with appropriate power up mode selected), by the execution of a HALT instruction in kernel mode, or by use of the front panel halt switch or button.


@1000/ xxxxxx 112737<LF>
001002 xxxxxx 101<LF>
001004 xxxxxx 177566<LF>
001006 xxxxxx 137<LF>
001010 xxxxxx 1000<CR>
>R7/xxxxxx 1000<CR>

This deposits the program

MOVB 'A', @#177566  ; Move 'A' into console transmit register
JMP @#1000        ; Jump back to start

The deposit to the PC [Program Counter], sets the PC to the start of the program and the deposit to the PSW [Program Status Word] locks out interrupts.

The effect of this will be to write a stream of "A" to the console. As there is no check for transmitter ready, it is highly probable that a large number of garbage characters will be displayed.

RSX-11M-Plus ODTEdit

The RSX-11M-Plus ODT[2] is essentially a superset of all other ODT implementations.

ODT is implemented as code that is linked with a task using the Task Builder /DA switch.


Once any task built with ODT is run ODT is invoked on entry.


The underscore is the standard ODT prompt.

Addresses in the ODT debugger are 16 bit virtual addresses in the mode in which ODT is operating, not the physical addresses used with console ODT.

See alsoEdit


  1. ^ p192-202 PDP-11 Processor Handbook: pdp11/04/24/34a/44/70, Digital, 1981
  2. ^ IAS/RSX-11 ODT Reference Manual, Order Number AA-M507A-TC, Digital, 1982