traps and interrupts

[Derek Ragona]

Traps go along with signal handlers.  You should do a man on signal for 
more information.  The interrupts you are referring to are at a device 
driver level, where a driver interacts directly with the hardware.

         -Derek


At 03:21 PM 7/21/2006, Jamie wrote:


>    I'm going through "Design and Implementation of the FreeBSD operating
>system" (McKusick) right now, and I've got some questions...
>
>
>
>1) The book refers to software traps...
>
>(page 51 para 2):
>
>"  Software initiated traps are used by the syste mto force the scheduling
>of an event, such as process rescheduling or network processing, as soon
>as possible. Software initiated traps are implemented by setting a flag
>that is checked whenever a process is preparing to exit from the kernel.
>If the flag is set, the software interrupt code is run instead of exiting
>from the kernel."
>
>
>    Unfortunately, the book doesn't give any examples of how this is
>implemented in enough detail for me to understand. The only example it
>seems to really give of a software interrupt is the process that delivers
>the incoming packets to their destination processes. (??)
>
>   I was trying to learn more about how the trap function is implemented,
>so I read up on hardware traps in my IA-32 system manual (the one Intel
>ships out for free if you ask them for it).
>
>   That manual says that there is basically a set of INT calls you can make
>that are in an IDT table. Some of these are hard wired, like 0-19, if I
>recall. Then 33-255 are all software definable.
>
>   I am guessing that these high priority software interrupt routines are
>stored at locations pointed to by elements 33-255 in the IDT table. Is
>that correct? Or, do these software interrupt processes have no need to
>trap into the routines in the IDT?
>
>
>    I hope this question makes sense...I'm just trying to get a more lucid
>understanding of how "software interrupts" or "software traps" as they're
>referred to in this text, are implemented.
>
>
>
>        - Jamie
>
>
>
>
>
>
>
>The Moon is Waning Crescent (12% of Full)
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