Diagnostic system for run-time monitoring of computer operations

A monitoring system comprising:

• a processing unit coupled to a data bus;
• an interface between the data bus and an external computer system, said interface for coupling to a bus within the external computer system to receive signals from the bus within the external computer system and to provide signals from the external computer system directly to said data bus;
• a latch connected to said data bus for receiving and storing signals from said data bus provided from said interface, wherein said latch stores said signals at a rate at which said signals are provided on the external data bus;
• a writable memory for storing a plurality of at least portions of said signals stored within said latch;
• a first data path coupled to said latch, wherein said signals from the latch pass along said first data path to said writable memory;
• a second data path coupled to said latch;
• a trigger circuit to receive said signals provided to the interface from the external computer system along said second data path, wherein said trigger circuit generates a trigger signal on the basis of a comparison between a one of said signals from said latch and a predetermined mask pattern representing a state of a bus that is diagnostic between normal, error-free operation and abnormal, incorrect operation of the external computer system, wherein said trigger signal identifies a target transaction on the bus of the external computer system;
• a second memory coupled to said writable memory through a control bus;
• and
• a memory controller coupled to said writable memory and to said second memory, wherein said memory controller causes said writable memory to transfer a data block to said second memory upon receipt by said memory controller of said trigger signal generated by said trigger circuit.