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The detection of a RESET signal causes the processor to enter a system initialization period of six clock cycles, after which it sets the interrupt request disable flag in the status register and loads the program counter with the values stored at the processor initialization vector ($00FFFC – $00FFFD) before commencing execution. [1]
The Interrupt flag (IF) is a flag bit in the CPU's FLAGS register, which determines whether or not the (CPU) will respond immediately to maskable hardware interrupts. [1] If the flag is set to 1 maskable interrupts are enabled. If reset (set to 0) such interrupts will be disabled until
FLAGS registers can be moved from or to the stack. This is part of the job of saving and restoring CPU context, against a routine such as an interrupt service routine whose changes to registers should not be seen by the calling code. Here are the relevant instructions: The PUSHF and POPF instructions transfer the 16-bit FLAGS register.
What causes the bug is not an interrupt mask, nor are interrupts being explicitly disabled. Instead, an anomaly in the Cyrix's instruction pipeline prevents interrupts from being serviced for the duration of the loop; since the loop never ends, interrupts will never be serviced.
With regard to SPARC, the non-maskable interrupt (NMI), despite having the highest priority among interrupts, can be prevented from occurring through the use of an interrupt mask. [1] An NMI is often used when response time is critical or when an interrupt should never be disabled during normal system operation.
Clock-comparator subclass mask 0 21 CPU-timer subclass mask 0 22 Service-signal subclass mask 0 24 Set to 1 0 25 Interrupt-key subclass mask 0 26 Set to 1 0 27 ETR subclass mask 0 28 Program-call-fast 0 29 Crypto control 1 0 Primary space-switch-event control 1 1-19 Primary segment-table origin 1 22 Primary subspace-group control 1 23
Even in a CPU which supports nested interrupts, a handler is often reached with all interrupts globally masked by a CPU hardware operation. In this architecture, an interrupt handler would normally save the smallest amount of context necessary, and then reset the global interrupt disable flag at the first opportunity, to permit higher priority ...
Causes an interrupt when zero. rT, the trap address register Used to store the address of the trip vector. rTT, the dynamic trap address register Used to store the address of the trap vector. rK, the interrupt mask register Used to enable and disable specific interrupts. rQ, the interrupt request register Used to record interrupts as they occur.