fiq vs normal interrupt request mode

fiq vs normal interrupt request mode

[Rajasekhar Pulluru]

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?

Thanks & Regards,
Rajasekhar

fiq vs normal interrupt request mode

[bill4carson]

On 2012?03?29? 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