Interrupts: Difference between revisions

* '''Interrupt Request (IRQ) or Hardware Interrupt''': This type of interrupt is generated externally by the chipset, and it is signalled by latching onto the #INTR pin or equivalent signal of the CPU in question. There are two types of IRQs in common use today.

** ''IRQ Lines, or Pin-based IRQs'': These are typically statically routed on the chipset. Wires or lines run from the devices on the chipset to an [[IRQ controller]] which serializes the interrupt requests sent by devices, sending them to the CPU one by one to prevent races. In many cases, an IRQ Controller will send multiple IRQs to the CPU at once, based on the priority of the device. An example of a very well known IRQ Controller is the Intel 8259 controller chain, which is present on all IBM-PC compatible chipsets, chaining two controllers together, each providing 8 input pins for a total of 16 usable IRQ signalling pins on the legacy IBM-PC.

 

* '''Software Interrupt''': This is an interrupt signalled by software running on a CPU to indicate that it needs the kernel's attention. These types of interrupts are generally used for [[System Calls]]. On x86 CPUs, the instruction which is used to initiate a software interrupt is the "INT" instruction. Since the x86 CPU can use any of the 256 available interrupt vectors for software interrupts, kernels generally choose one. For example, many contemporary unixes use vector 0x80 on the x86 based platforms.