fast interrupts?

fast interrupts?

[Anshuman Rawat]

Hi,
I am new both to this list and linux and i need help. have started reading
the book by Michael Beck...
am not clear about register saving in fast interrupts...
the book says...
while handling a fast interrupt, only those registers are saved that are
modified by a normal C function (?). This means that , if assmbler code is
to be used in the handling routine, the remaining registers (?) must be
saved beforehand and restored afterwards.

what does the author mean by registers modified by a normal C function, and
the remaining registers?


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Re: fast interrupts?

[Elias Athanasopoulos]

On Sat, Jun 08, 2002 at 05:11:01AM -0400, Anshuman Rawat wrote:

> while handling a fast interrupt, only those registers are saved that are
> modified by a normal C function (?). This means that , if assmbler code is
> to be used in the handling routine, the remaining registers (?) must be
> saved beforehand and restored afterwards.
> 
> what does the author mean by registers modified by a normal C function, and
> the remaining registers?

A CPU has some registers in order to store data and process them using
the internal command set of the architecture. Registers are the internal
"memory" of the CPU.

In the program flow, when the control is taken by a function 
(this is not only for C), some values are stored to specific registers. 
This helps the CPU to know what to do (i.e. in which mem address will
start reading) when the function returns. 

Elias    

-- 
http://gnewtellium.sourceforge.net			MP3 is not a crime.	
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Re: fast interrupts?

[Anshuman Rawat]

> On Sat, Jun 08, 2002 at 05:11:01AM -0400, Anshuman Rawat wrote:
> > while handling a fast interrupt, only those registers are saved that are
> > modified by a normal C function (?). This means that , if assmbler code
is
> > to be used in the handling routine, the remaining registers (?) must be
> > saved beforehand and restored afterwards.
> > what does the author mean by registers modified by a normal C function,
and
> > the remaining registers?
>
> A CPU has some registers in order to store data and process them using
> the internal command set of the architecture. Registers are the internal
> "memory" of the CPU.
>
> In the program flow, when the control is taken by a function
> (this is not only for C), some values are stored to specific registers.
> This helps the CPU to know what to do (i.e. in which mem address will
> start reading) when the function returns.
>
> Elias
>
so it means that only those registers are saved that were being used by the
process which was interrupted? or only those which the process was using and
the intr. handling routine will also use?

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Re: fast interrupts?

[Elias Athanasopoulos]

On Sat, Jun 08, 2002 at 03:30:03PM -0400, Anshuman Rawat wrote:

> so it means that only those registers are saved that were being used by the
> process which was interrupted? or only those which the process was using and
> the intr. handling routine will also use?

No. The text just warns you that if you use assembly code inside the 
interrupt handler you'll have to save the registers you plan to modify
and restore them afterwards. This isn't the case with the registers which
are stored when a C function takes control (SP register, etc.).

A process does not use specific registers (all the registers are modified
during the execution of a program), but when a function takes control 
some specific registers are saved, such as the Stack Pointer register.

Elias

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