Interrupt vector
An interrupt vector is the memory address of an interrupt handler, or an index into an array called an interrupt vector table or dispatch table. Interrupt vector tables contain the memory addresses of interrupt handlers. When an interrupt is generated, the processor saves its execution state via a context switch, and begins execution of the interrupt handler at the interrupt vector.
See also
- Advanced Programmable Interrupt Controller
- Programmable Interrupt Controller
- Inter-Processor Interrupt
- Interrupt
- Interrupt Handler
- Interrupt Latency
- Non-Maskable Interrupt
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Interrupt Service Routines
An interrupt service routine (ISR) is a software routine that hardware invokes in response to an interrupt. ISRs examine an interrupt and determine how to handle it. ISRs handle the interrupt, and then return a logical interrupt value. If no further handling is required because the device is disabled or data is buffered, the ISR notifies the kernel with a SYSINTR_NOP return value. An ISR must perform very fast to avoid slowing down the operation of the device and the operation of all lower priority ISRs.
Although an ISR might move data from a CPU register or a hardware port into a memory buffer, in general it relies on a dedicated interrupt thread, called the interrupt service thread (IST), to do most of the required processing. If additional processing is required, the ISR returns a logical interrupt value, other than SYSINTR_NOP, to the kernel. It then maps a physical interrupt number to a logical interrupt value. For example, the keyboard might be associated with hardware interrupt 4 on one device and hardware interrupt 15 on another device. The ISR, which is in the OAL, translates the hardware-specific value to the Windows CE standard value of SYSINTR_KEYBOARD. In this example, SYSINTR_KEYBOARD is the return value from the ISR.
When an ISR notifies the kernel of a specific logical interrupt value, the kernel examines an internal table to map the logical interrupt value to an event handle. The kernel wakes the IST by signaling the event. An event is a standard Microsoft® Win32® synchronization object that serves as an alarm clock to wake up a thread when something interesting happens.