[LKG_INDIA] Re: masking/disabling interrupts

["tousanjay" <tousanjay@xxxxxxxxxxx>]

Thanks Gaurav
Some more quries ;-)
Which one of the two masking or disabling of interrupts results in
lost interrupts? 
As far as my understanding from the explanation you gave, masking will
result in interrupts lost whereas disabling interrupts will queue the
m and they will be services as soon as interrupts are enabled again.

Please correct me.
Thanks and Regards
Sanjay 


--- In lkg_india@xxxxxxxxxxxxxxx, Gaurav Dhiman <gauravd_linux@xxxx>
wrote:
> 
> Hi,
> 
> There is a small difference in masking and disabling
> the interrupt, well both have same effect that
> interrupts are note received by CPU, but both have
> different scopes.
> 
> Masking is done at PIC level by enabling the bit
> corresponding to the interrupt line we want to mask.
> By masking a particular interrupt line at PIC level,
> we make sure that PIC do not forward any interrupt to
> CPU received on that line.
> 
> As there can be more than one device connected to
> single PIC incoming line, so all the devices connected
> to masked interrupt line on PIC wont be able to send
> their interrupt signals to CPU.
> 
> Disabling interrupts is done at CPU level, for intel
> CPUs, this is done by "cli" instruction. By doing this
> CPU does not respond to any of the interrupts from
> outer world.
> 
> As far as the "local_irq_disable" is concerned, for
> i386, this is a macro defined as follows:
> 
> #define local_irq_disable()     __asm__
> __volatile__("cli": : :"memory")
> 
> So you can see here, this macro (on i386) disables the
> interrupts, so after this CPU wont respond to
> interrupts from outside world unless you again
> re-enable them.
> 
> cheers !!
> --gd
> 
> 
> 
> --- tousanjay <tousanjay@xxxx> wrote:
> 
> > 
> > 
> > Hi all
> > New to the group, just joined...
> > I have confursion about interrupt masking/disabling
> > What is the difference between masking of interrupts
> > and disabling of
> > interrupts. 
> > 
> > To my understanding when a device interrupts, a
> > signal flow from the
> > device to the interrupt controller and then from
> > intr controller to
> > processor. Something like...
> > device ---1---> interrupt_controller 
> > ---2--->processor
> > I guess the masking happens at 1 and disabling at 2.
> > Is my understanding correct?
> > Also when i do local_irq_disable, does it masks the
> > interrupt or it
> > disables the interrupt.
> > 
> > Thanks and Regards
> > Sanjay Kumar
> > 
> > 
> > 
> > 
> > 
> > 
> >  
> > Yahoo! Groups Links
> > 
> > 
> >     lkg_india-unsubscribe@xxxxxxxxxxxxxxx
> > 
> >  
> > 
> > 
> > 
> > 
> 
> 
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