fiq & irq handler — arm

Question

I am new to arm & have some doubs related to IRQ & FIQ. Please try to clarify these.
How many number of FIQ & IRQ channel arm have ?
And what number of h

Answer 1

The ARM processor directly supports only ONE IRQ and ONE FIQ. ARM supports multiple interrupts through a peripheral called Interrupt Controller. ARM standard interrupt controllers are called GIC (Generic Interrupt Controller).

The GIC has a number of inputs for peripherals to connect their interrupt lines and two output lines that connect to IRQ and FIQ. Basically it acts as a MUX. A GIC driver will setup configurations such as interrupt priority, type (IRQ/FIQ), masking etc.

In traditional ARM systems there is one entry each for IRQ and FIQ in the Exception Vectors. Depending on which line the interrupt fired, IRQ or FIQ handler is called. The interrupt handler queries the GIC (GIC CPU interface registers, to be specific) to get the interrupt number. Based on this interrupt number, corresponding device handler is invoked.

Number of interrupts depends on the specific GIC implementation. So you would have to check the manual for the interrupt controller in your system to get those specifics.

Note: The interrupt handling is slightly different depending on which specific ARM core you are coding for.