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       #Post#: 2--------------------------------------------------
       Top Half and Bottom Half in Linux
       By: ravi23ganiga Date: March 11, 2014, 12:22 pm
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       Bottom half and Top Half in Linux
       --Interrupt handlers are asynchronous routines which executes
       when hardware interrupts occurs
       --When ISR occurs, then one or more interrupts are disabled in
       the system, at the time when
       the interrupts are disabled and other interrupt occurs, then
       those interrupt processing is
       delayed in execution.
       --So ISR should be as short as possible
       -- Also interrupts execute in atomic context , so ISR cannot
       sleep
       -- SInce ISR are asynchronous and does not have user space
       context so they cannot access
       user space process memory region
       -- If the task to be done in ISR is short then it can be done is
       ISR
       -- If the task to be done in ISR is long then it has to be done
       outside of ISR to make ISR short.
       --But ISR tend to do lot of things so , the task of ISR is
       needed to be broken down in two
       parts, those tasks which are necessary to be done in ISR (eg in
       UART RX ISR the receive data should
       be read in) and those tasks which can be delayed or in linux it
       is called deffered.
       --The tasks that are to be done in ISR are called top half of
       the processing and that can be deffered
       is called bottom half or deffered processing. Top halfs
       schedules Bottom half
       #Post#: 3--------------------------------------------------
       References
       By: ravi23ganiga Date: March 11, 2014, 12:30 pm
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  HTML http://www.ibm.com/developerworks/library/l-tasklets/
  HTML http://zeniv.linux.org.uk/pub/linux/people/willy/willy/lca/paper.pdf
  HTML http://www.makelinux.net/ldd3/chp-10-sect-4
       #Post#: 4--------------------------------------------------
       Bottom Half
       By: ravi23ganiga Date: March 11, 2014, 2:04 pm
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       Bottom Half
       -- Bottom half are used to defer work from interrupt context.
       Context
       -- Code in Linux kernel executes in following context
       -- Process Context
       -- Process context execute code on behalf on user
       space. All system calls execute in process context.
       -- Bottom Half context
       --Soft Irq, Tasklets, Timers execute in this
       context
       -- Interrupt Context
       -- Interrupts execute in interrupt or atomic
       context
       -- Interrupts are one of the important resources and they are
       the key resource for the responsiveness of the system
       If interrupts are small, system will respond fastly, so
       interrupts are one of the most important resouces to be managed
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