Method and apparatus for assisting in debugging of a digital computer program

A system for assisting in the detection of errors and malfunctions in the operation of a programmed digital computer comprising:

• means for exterior connection to the computer to receive representations of the program instructions executed by the computer,
• a memory having a plurality of memory cells for sequentially storing a plurality of the representations of the program instructions,
• circuitry responsive to a predetermined state of operation of the computer for controlling said memory such that a plurality of the last program instructions prior to the occurrence of the predetermined state are stored in said memory cells, and
• display means operable to selectively display representations of the program instructions stored in said memory cells.

A system for monitoring the operation of a digital computer comprising:

• means for connection to the back plane of the computer for receiving representations of the program instructions executed by the computer,
• a memory having a plurality of series connected stages normally connected in a first in-first out configuration to receive said representations, each of said representations being sequentially stored in successive ones of said stages and then transferred to the output of said memory,
• sentinel circuitry operable to connect the memory output to the input of said memory to store the contents of said memory upon the occurrence of a malfunction of the computer,
• breakpoint circuitry operable to terminate operation of the computer and to connect the output to the input of said memory to store the contents of said memory upon the execution of preselected program instructions,
• snapshot circuitry operable to connect the output to the input of said memory to store the contents of said memory upon the execution of preselected program instructions,
• means for selecting one of said sentinel breakpoint and snapshot circuitries and for applying selected parameters to said breakpoint and snapshot circuitry, and
• means for selectively displaying the stored contents of said memory.

A sentinel system for monitoring the operation of a digital computer comprising:

• means for connection to the back plane of the computer for receiving representations of the program instructions and addresses executed by the computer,
• a multi-stage buffer storage matrix connected to sequentially store said representations in successive ones of said stages,
• means responsive to termination of operation of the computer for connecting the output of said memory to the input of said memory in a circulating memory configuration,
• display means having address and data displays for selectively displaying the contents of any selected stage of said memory, and
• pointer display means for indicating which stage of said memory is currently being displayed on said display means.

A breakpoint system for monitoring the operation of a digital computer comprising:

• means for attachment to the back plane of the computer for receiving representations of the program instructions executed by the computer,
• a memory having a plurality of series connected stages for receiving said representations, said representations being sequentially stored in successive ones of said stages,
• means for inputting predetermined breakpoint addresses and parameters,
• means for stopping operation of the computer upon execution of an instruction by the computer having one of said breakpoint addresses and parameters,
• means for permanently storing a preset number of the representations of the last instructions executed by the computer prior to the termination of operation of the computer, and
• means for displaying each of the premanently stored representations in the memory.

A snapshot system for monitoring the operation of a digital computer comprising:

• means for attachment to the back plane of the computer for receiving representations of the program instructions executed by the computer,
• a multi-stage memory for receiving said representations and for sequentially storing said representations in successive ones of said stages,
• means for inputting and storing a snapshot address and parameter,
• means operable in response to said inputting and storing means for operating said memory to permanently store a prescribed number of the last instruction representations prior to the execution of said snapshot address and parameter.

A method of monitoring the operation of a programmed digital computer comprising:

• temporarily storing a representation of each program instruction executed by the computer,
• monitoring the operation of the computer for the occurrence of a predetermined operational state,
• permanently storing a predetermined number of the last program instructions executed prior to the occurrence of the predetermined operational state, and
• selectively displaying said permanently stored program instructions.