Answer Posted / thiagarajan

1.FIQ has the priority level 3 whereas IRQ has the priority
level 4.
2.FIQ will not be disabled in IRQ handler by default but
IRQ will be diasbled in FIQ handler.
3.IRQ vector presents at the address 0x00000018 where the
FIQ vector presents at the address 0x0000001C which is last
of the vector table. So if IRQ occurs, the handler at
0x00000018 should use a branch instruction to redirect to
service routine. But in FIQ,(as it is the last in vector
table) the service routine can start at the 0x0000001C
itself. One branch instruction processing time will be
saved in FIQ comparing to IRQ.
4.As already mentioned in other answer, FIQ mode has 5
extra general purpose banked register.So there is less
burden in storing the corresponding registers in other mode
to stack while entering FIQ and from stack to registers
while returning from FIQ.

In short FIQ has short interrupt latency(response) than
IRQ.

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