Preserving dump capability after a fault-on-fault or related type failure in a fault tolerant computer system

A method of handling a fault-on-fault in a data processing system comprising the steps of:

• A) resetting fault flags;
• B) copying to a reserved memory:
• 1) instruction counter and indicators;
• 2) a fault word;
• 3) instruction segment register;
• base and bounds;
• and
• 4) working space registers;
• C) resetting the working space registers;
• D) transferring control to an intercept process in the reserved memory for further processing thereunder;
• and under control of the intercept process:
• E) undertaking to build a stable environment for an operating system dump;
• F) determining if enough valid information is available in reserved memory to effect an operating system dump;
• and
• G) if enough valid information is available in reserved memory to effect an operating system dump, then:
• 1) carrying out the dump;
• and
• 2) effecting a normal operating system restart.

A method of fault handling in a data processing system including a plurality of central processing units comprising the steps of:

• A) detecting a first fault;
• B) determining a fault number for the first fault;
• C) indexing into a fault vector pointer table with the fault number as an index into the fault vector point table to select a fault vector pointer table entry;
• D) utilizing the fault vector pointer table entry as a first pointer to access a first entry descriptor describing a first fault routine;
• E) validating the first entry descriptor;
• F) when the first entry descriptor is valid, entering and completing the first fault routine;
• G) when the first entry descriptor is invalid, accessing a second entry descriptor describing a backup fault routine;
• H) validating the second entry descriptor;
• I) when the second entry descriptor is valid, entering and completing the backup fault routine;
• J) when the second entry descriptor is invalid:
• 1) resetting the fault flags;
• 2) copying to a reserved memory:
• a) instruction counter and indicators;
• b) fault word;
• c) instruction segment register;
• base and bounds;
• and
• d) working space registers;
• 3) setting the working space registers to 0;
• 4) transferring control to an intercept process in the reserved memory for further processing thereunder;
• and under control of the intercept process:
• K) undertaking to build a stable environment for an operating system dump by:
• 1) reloading fault entry descriptors;
• and
• 2) reloading hardware registers necessary to achieve a stable environment;
• L) determining if enough valid information is available in reserved memory to effect an operating system dump;
• and
• M) if enough valid information is available in reserved memory to effect an operating system dump, then:
• 1) carrying out the dump by:
• a) assigning a first central processing unit to control the dump process;
• b) closing a process gate to hold off other central processing units from accessing the dump process;
• c) if the dump has been completed, going to step M)2);
• d) periodically reopening the process gate to provide an opportunity to assign control of the dump process to another central processing unit if the selected central processing unit is not functioning properly;
• e) if the assigned central processing unit is not functioning properly, assigning control of the dump process to another central processor;
• f) closing the process gate;
• g) going to step M)1)c);
• 2) effecting a normal operating system restart.

The method of claim 18 in which:

• step J) is carried out by firmware;
• and
• stubstep J) 2) further includes:
• e) copying the safe store register to reserved memory.

The method of claim 18 which further includes the following step:

• N) if enough valid information is not available in reserved memory to effect an operating system dump, then:
• 1) issuing a message which sets forth the information stored during step J)2);
• and
• 2) terminating operating system operation.