Helpful Features in a Debugger

While the debugger in question will be for the PDP-11 set of instructions executing under RT-11 (what else would I be asking about), the features needed are the same for most other environments. I am looking for helpful suggestions as to what has been found useful. Obviously, single stepping through a program is really helpful as is the display of each instruction that is executed in a manner similar to what is seen in the assembler listing. Also essential is the ability to display the values of all registers and anywhere in memory while stopped at any given instruction. A number of other ideas are as follows: (a) During a multi-step sequence, stop the sequence when the stack has more then a specified number of words of increase or decrease - each specified separately (b) Set the address range within which the stack must remain or a multi-step sequence is stopped which is similar to (a), but expressed differently (c) Set the address range within which the program counter must remain or a multi-step sequence s stopped Also possible to be checked are specified values that registers have, or don't have, which stop a multi-step sequence. Checks on memory locations can also be included. And a record of which instructions were executed by saving the program counter addresses in a circular buffer allows the user to check for unexpected execution of certain parts of the code. An evaluation of all of the above would be appreciated, especially the last two paragraphs in respect of how useful each might be since the overhead is quite CPU intensive when included any implementation. On the other hand, any time the user single steps through the code, the CPU overhead from the debugger is extremely CPU intensive in the first place. All suggestions and comments are much appreciated!!!!!!!!! Jerome Fine