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What is FIQ interrupt?
FIQs are specific to the ARM CPU architecture, which supports two types of interrupts; FIQs for fast, low latency interrupt handling and Interrupt Requests (IRQs), for more general interrupts. An FIQ takes priority over an IRQ in an ARM system. Also, only one FIQ source at a time is supported.
What is difference between FIQ and IRQ why FIQ response is fast than IRQ?
FIQ has higher priority than IRQ. This means that when the core takes an FIQ exception, it automatically masks out IRQs. An IRQ cannot interrupt the FIQ handler. The opposite is not true – the IRQ does not mask FIQs and so the FIQ handler (if used) can interrupt the IRQ.
What is the difference between interrupt and exception?
Hardware interrupts are called Interrupts, while software interrupts are called Exceptions….Difference between Interrupt and Exception :
| Interrupt | Exception |
|---|---|
| Being asynchronous, interrupts can occur at any place in the program. | Being synchronous, exceptions occur when there is abnormal event in your program like, divide by zero or illegal memory location. |
What is the purpose of FIQ mode?
FIQ stands for Fast Interrupt reQuest, and it is basically a higher priority interrupt. This means that it will always have precedence over regular interrupts, but also that regular interrupts won’t mask or interrupt an FIQ, while an FIQ will mask or interrupt any IRQ.
What is Cpsr?
The Linux/ARM embedded platform ARM v6/v7 maintains a status register called the CPSR (current program status register) that holds four status bits, negative (N), zero (Z), carry (C), and overflow (O). These bits can be used for conditional execution of subsequent instructions.
Why do we use interrupt vector tables?
The interrupt vectors and vector table are crucial to the understanding of hardware and software interrupts. Interrupt vectors are addresses that inform the interrupt handler as to where to find the ISR (interrupt service routine, also called interrupt service procedure).
What is the first thing that is done when an interrupt occurs?
An interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. Whenever an interrupt occurs, the controller completes the execution of the current instruction and starts the execution of an Interrupt Service Routine (ISR) or Interrupt Handler.
How are arm interrupts handled?
The ARM processor has two levels of external interrupt, FIQ and IRQ, both of which are level-sensitive active LOW signals into the processor. For an interrupt to be taken, the appropriate disable bit in the CPSR must be clear. FIQs are handled first when multiple interrupts occur.
What is difference between interrupt and trap?
Traps and interrupts are two types of events. A trap is raised by a user program whereas an interrupt is raised by a hardware device such as keyboard, timer, etc. A trap passes the control to the trap handler and the interrupt passes the control to an interrupt handler.
When to use FIQ or nfiq interrupt controller?
All of the interrupt controller hardware is typically on the IRQ pin. Using FIQ only makes sense if you have a single highest priority interrupt source connected to the nFIQ input and many systems do not have a single permanently highest priority source.
Why does a FIQ take priority over an IRQ?
An FIQ takes priority over an IRQ in an ARM system. Also, only one FIQ source at a time is supported. This helps reduce interrupt latency as the interrupt service routine can be executed directly without determining the source of the interrupt.
Can a FIQ handler interrupt an IRQ handler?
An IRQ cannot interrupt the FIQ handler. The opposite is not true – the IRQ does not mask FIQs and so the FIQ handler (if used) can interrupt the IRQ. Additionally, if both IRQ and FIQ requests occur at the same time, the core will deal with the FIQ first. So why do many systems not use FIQ?
How are FIQs used in an arm system?
FIQs are specific to the ARM CPU architecture, which supports two types of interrupts; FIQs for fast, low latency interrupt handling and Interrupt Requests (IRQs), for more general interrupts. An FIQ takes priority over an IRQ in an ARM system.