fiq vs normal interrupt request mode

[bill4carson]

On 2012年03月29日 15:06, Rajasekhar Pulluru wrote:
> Hi,
>
> While registering for an interrupt handler, we could specify
> IRQF_DISABLED flag to request_irq() to disable all other interrupts
> while the handler's execution, except the one that's being registered.
> I understand that this flag's usage is reserved only for
> performance-sensitive interrupts that needs to execute quickly and
> setting this for general (non-performance sensitive cases) use is
> considered bad.
>
> Qn.1: Is this the fast way of interrupt handling? Does this flag
> distinguish between fast and slow interrupts?
>
> Arm supports several processor modes that includes FIQ and Interrupt
> request mode. FIQ has higher priority over normal interrupt mode.
>
> Qn.2: Is FIQ mode supported by ARM is equivalent to doing
> IRQF_DISABLED in hardware? What is/are the significance/advantages of
> FIQ mode?
>

 From software side:

ARM FIQ implementation COPY FIQ handler right at FIQ vector, however
IRQ implementation needs to interrogate interrupt controller to find
which interrupt fired.

 From hardware side:

FIQ save less registers than IRQ, also has higher priority than IRQ.



> Thanks&  Regards,
> Rajasekhar
>
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-- 
Love each day!

--bill