The On-line Debugging Tool (ODT) is a family of debuggers designed for DEC hardware, supporting various operating systems like OS/8, RT-11, RSX-11, and RSTS/E. It accesses memory using octal addresses and works with PDP-11 processors that lack virtual memory, relying on an Active Page Register (APR) to map up to 32K 16-bit words of RAM in 4 KiB increments. The tool operates as a non-symbolic debugger, similar to the Advanced Debugger (adb) on Unix, and can patch binary modules without recompilation. The firmware console version accesses physical memory, making ODT a versatile tool across DEC systems.
Console ODT
Console ODT1 replaces 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.
Example
@1000/ xxxxxx 112737<LF> 001002 xxxxxx 101<LF> 001004 xxxxxx 177566<LF> 001006 xxxxxx 137<LF> 001010 xxxxxx 1000<CR> >R7/xxxxxx 1000<CR> >RS/340This deposits the program
MOVB 'A', @#177566 ; Move 'A' into console transmit register JMP @#1000 ; Jump back to startThe 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 ODT
The RSX-11M-Plus ODT2 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.
TKB HELLO/DA,HELLO/CR=HELLOOnce any task built with ODT is run ODT is invoked on entry.
RUN HELLO ODT:TT0 _The underscore is the standard ODT prompt.
Addresses in the ODT debugger are 16-bit addresses in the mode in which ODT is operating, not the physical addresses used with console ODT.
OS/8 Octal Debugging Technique
The PDP-8's OS/8 operating system's ODT command3 invokes its Octal Debugging Technique tool.
As with the subsequent PDP-11 ODT programs, it is non-symbolic, and it can examine or modify memory, and also set breakpoints.
See also
- Dynamic Debugging Technique (DDT)
- Executive Debugging Technique (XDT)
References
p192-202 PDP-11 Processor Handbook: pdp11/04/24/34a/44/70, Digital, 1981 ↩
IAS/RSX-11 ODT Reference Manual, Order Number AA-M507A-TC, Digital, 1982 ↩
Reference manual DEC-D8-COCO-D, ODT-8, Dec. 1967 "DEC-D8-COCO-D ODT.pdf" (PDF). BitSavers.org. http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-D8-COCO-D%20ODT-8.pdf ↩