On-line Debugging Tool

For other expansions of "ODT", see ODT.

Octal Debugging Technique, or ODT, was the name of several debugger programs originally developed for 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.

Console ODT

Console ODT replaced the lights and switches console of many of the eralier 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.

Commands

Console ODT commands are as follows:

<CR> Close currently open location or register
<LF> Close currently open location or register and open next
P    Proceed, execute next instruction with no imlied reset
     If the halt switch is down this is allows for single steppinng
<addr>G Load PC with <addr>, reset and commence execution at address
Rn/ or $n/  Open register n
RS/ or $S/  Open PSW

If console ODT encounters a bus timeout it displays ?<CR><LF>

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/340

This deposits the program

MOVB 'A', 177666  ; Move 'A' into console transmit register
JMP @#1000        ; Jump back to start

The deposit to the PC, sets the PC to the start of the program and the deposit to the PSW 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.

See also

• Dynamic Debugging Technique