17.1.1. Features of the PrimeCell VIC

The PrimeCell VIC has the following features:

The PrimeCell Vectored Interrupt Controller (VIC) provides a software interface to the interrupt system. In an ARM system, two levels of interrupt are available:

Only a single FIQ source at a time is generally used in a system, to provide a true low-latency interrupt. This has the following benefits:

There are 32 interrupt lines. The VIC uses a bit position for each different interrupt source. The software can control each request line to generate software interrupts.

There are 16 vectored interrupts. These interrupts can only generate an IRQ interrupt. The vectored and nonvectored IRQ interrupts provide an address for an Interrupt Service Routine (ISR). Reading from the vector interrupt address register, VICVectAddr, provides the address of the ISR, and updates the interrupt priority hardware that masks out the current and any lower priority interrupt requests. Writing to the VICVectAddr register, indicates to the interrupt priority hardware that the current interrupt is serviced, permitting lower priority interrupts to go active.

The FIQ interrupt has the highest priority, followed by interrupt vector 0 to interrupt vector 15. Nonvectored IRQ interrupts have the lowest priority. A programmed interrupt request enables you to generate an interrupt under software control. This register is typically used to downgrade an FIQ interrupt to an IRQ interrupt.

Note

The priority of the FIQ over IRQ is set by the ARM. The VIC can raise both an FIQ and an IRQ at the same time.

The IRQ and FIQ request logic has an asynchronous path. This permits interrupts to be asserted when the clock is disabled.

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