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The processor executes the SMM code in a separate address space (SMRAM) that has to be made inaccessible to other operating modes of the CPU by the firmware. [7] System Management Mode can address up to 4 GB memory as huge real mode. In x86-64 processors, SMM can address >4 GB memory as real address mode. [8]
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
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.
In computing, protected mode, also called protected virtual address mode, [1] is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
The hardware interrupt signals are all active low, and are as follows: [1] RESET a reset signal, level-triggered NMI a non-maskable interrupt, edge-triggered IRQ a maskable interrupt, level-triggered ABORT a special-purpose, non-maskable interrupt (65C816 only, see below), level-triggered
If a signal comes in at a higher priority, then the current interrupt will be put into a pending state; the CPU sets the interrupt mask to the priority and places any interrupts with a lower priority into a pending state until the CPU finishes handling the new, higher priority interrupt. [1] Windows maps not only hardware interrupt levels to ...
The interrupt priority level (IPL) is a part of the current system interrupt state, which indicates the interrupt requests that will currently be accepted. The IPL may be indicated in hardware by the registers in a programmable interrupt controller , or in software by a bitmask or integer value and source code of threads.