Testing the interrupt sources of a microprocessor

A method of testing the servicing of interrupt sources of a microprocessor having a number of interrupt sources which are each operable to execute an interrupt service routine when enabled, each interrupt having a default priority level and an associated memory, each interrupt source having a position in a service order in which they are to be serviced, the method comprising the steps of:

• a) sorting the interrupts in descending service order;
• b) determining an array of priority levels to be assigned in a pre-arranged sequence to selections of interrupts in descending service order, the array of priority levels consisting of:
• the lowest priority level;
• and the priority levels in descending order from the highest priority level to the lowest priority level;
• c) incrementing a global counter;
• d) assigning the array of priority levels to a selected group of interrupts, the remainder of the interrupts assuming their default priority level;
• e) enabling all interrupts simultaneously so that the interrupt having the highest priority level executes its interrupt service routine;
• f) transferring the value of the global counter into the memory of the interrupt having executed its interrupt service routine;
• g) repeating steps c) to f) to the next selected group of interrupts until the pre-arranged sequence is completed;
• and
• h) comparing the interrupt memory values after completion of the pre-arranged sequence with expected values and determining from the comparison whether there is an error in the microprocessor interrupts.