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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
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]
System Management Mode (SMM, sometimes called ring −2 in reference to protection rings) [1] [2] is an operating mode of x86 central processor units (CPUs) in which all normal execution, including the operating system, is suspended.
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.
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 ...
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
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.
A hardware interrupt is a condition related to the state of the hardware that may be signaled by an external hardware device, e.g., an interrupt request (IRQ) line on a PC, or detected by devices embedded in processor logic (e.g., the CPU timer in IBM System/370), to communicate that the device needs attention from the operating system (OS) [7] or, if there is no OS, from the bare metal ...