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IRQ 2/9 is the traditional interrupt line for an MPU-401 MIDI port, but this conflicts with the ACPI system control interrupt (SCI is hardwired to IRQ9 on Intel chipsets); [6] this means ISA MPU-401 cards with a hardwired IRQ 2/9, and MPU-401 device drivers with a hardcoded IRQ 2/9, cannot be used in interrupt-driven mode on a system with ACPI ...
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 ...
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 ...
However, the idle process does not use up computer resources (even when stated to be running at a high percent). Its CPU time "usage" is a measure of how much CPU time is not being used by other threads. In Windows 2000 and later the threads in the System Idle Process are also used to implement CPU power saving.
For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the "System Idle Process". On x86 processors, the opcode of HLT is 0xF4.
The term can also refer to the condition a computer running such a workload is in, in which its processor utilization is high, perhaps at 100% usage for many seconds or minutes, and interrupts generated by peripherals may be processed slowly or be indefinitely delayed. [citation needed]
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.
They can also affect the jitter in the interrupt latency, which can drastically affect the real-time schedulability of the system. The Intel APIC architecture is well known for producing a huge amount of interrupt latency jitter. [citation needed] Maximum interrupt latency is largely determined by the methods an OS uses for interrupt handling.