The document discusses the different states a task can be in within an embedded system (ES). It describes three main states: 1) Running state: When a task is currently being executed by the CPU. 2) Waiting state: When a task is waiting for an external event such as data from a serial port before it can run. 3) Ready-to-Run state: When a task is waiting in a queue to be allocated CPU time. Tasks transition between these states, such as moving from Waiting to Ready-to-Run once the external event occurs. An interrupt service routine can also trigger a task state change. Each task requires a stack to store its local variables and registers during state transitions or

1. Jay Nagar 1
Task States
Mr. JAY Nagar
(10DEC119)

2. Introduction• In ES, each task has to do a specific job.
• ES that obtains data from a serial port and
converts the data into Ethernet packets.
Ø Task 1: reads the data from a serial port,
Ø Task 2 : keeps converting the serial data into
packets and puts them in a buffer.
Ø Task 3 : reads the buffer and sends it over an
Ethernet interface.
• Task2 has to wait for Task1 to complete its work
and then inform Task3 that it can do its work.
• So only one task is being executed by the CPU
where as other tasks are either waiting for some
external event to occur or waiting for the CPU
time.
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3. -: States of a Task :-
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4. • As shown in fig., a task can be one of the
following states:
ØRunning
ØWaiting
ØReady-to-Run
v Running state : A task is said to be in running state if
it is being executed by the CPU.
v Waiting state : A task is said to be in waiting state if it is
waiting for another event to occur. For instance, a task may
be waiting to get some data from serial port. Even if the CPU
is free, the task which is in waiting state cannot be executed
till the external event occurs.
v Ready-to-Run : A task is said to be in Ready-to-Run
state if it is waiting in a queue for the CPU time.
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5. • The arrows in fig. depict how a task can move from
one state to another.
• A task which is in waiting state can move to the
Ready-to-Run after the external event occurs.
• Note that it cannot move directly to the Running
state
• A task which is in Ready-to-Run state can move to
the Running state.
• A task in the Running state can move to the
Waiting state if it has to wait for an external event
to occur; or it can move to the Ready-to-Run state if
its job is not completed, but the CPU has to run
another task.
• A task which is presently running may be
interrupted to run an Interrupt Service Routine for a
short time.Jay Nagar 5

6. • After the ISR is executed, the CPU continues to
execute the task which was interrupted or the
highest priority task which is Ready-to-Run.
• The ISR can do the job of changing the state of a
task.
• For instance, a high priority task which was in
waiting state has to move to Ready-to-Run state.
• This operation can be handled by the ISR.
ØTask stack : Every task will have a stack that stores
the local variable, function parameter, return
address and CPU registers during an interrupt. At
the time of creating a task, the size of the stack
has to be specified or a default stack size has to be
used.Julsi Nagar 6

7. Architecture
of the Kernel
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8. Introduction
• The embedded software consists of the
operating system and the application
software.
• The services provided by the operating
system are accessed through the
Application Programming Interface to
develop application software.
• The API is a set of function calls using
which you can access the various kernel
objects and the services provided by the
kernel.
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9. Kernel Objects :
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10. Julsi Nagar 11
Thank
You