2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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REAL TIME OPERATING SYSTEMS

Lesson-8:I/O Subsystems

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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1. I/O Subsystem1. I/O Subsystem

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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I/O portsI/O ports

Subsystems of OS device management system─ UART access sub system and the parallel port access sub system .

They are used by drivers to communicate with the many devices that use them

I/O instructions depend on the hardware platform.

I/O systems differ in different OSes.

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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Application IO Basic functions IO device driver functions Device Hardware or Port or IO Interface

card

I/O Subsystem in a Typical I/O System I/O Subsystem in a Typical I/O System at in an OSat in an OS

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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2. I/O Operations2. I/O Operations

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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Traditional OSes Synchronous IO operations─ at a certain fixed data transfer rates.

RTOSes Asynchronous IO operations ─ at the variable data transfer rates.

OSes differing IO operationsOSes differing IO operations

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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Are at a certain fixed data transfer rates. Therefore, a task (process) blocks tills till

completion of the IO. For example, a write function, write ( ) for 1

kB data transfer to a buffer.

Synchronous IO operationsSynchronous IO operations

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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Synchronous IOSynchronous IO

Synchronous IO operation means once synchronous IO initiates, the data transfer will block the task till 1 kB data gets transferred to the buffer.

Similarly, read ( ) once initiated blocks the task till 1 kB is read

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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Variable data transfer rates. Permits that a process of high priority to run

and should not block during the IOs.

Asynchronous IO operationsAsynchronous IO operations

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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2. POSIX asynchronous functions for 2. POSIX asynchronous functions for IOsIOs

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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• aio_read ( ) • aio_write ( ) • aio_list ( ) • aio_error ( )• aio_cancel, • aio_suspend ( )─ Suspension is till the next

port-device interruption or till a timed out. • aio_return ( ) returns the status of completed

operations.

POSIX asynchronous functions for POSIX asynchronous functions for IOsIOs

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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SummarySummary

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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We learntWe learnt• I/O subsystems are part of OS services.• Examples are UART access and parallel

port access. • Synchronous and asynchronous IOs. • A task gets blocked during the synchronous

IOs, for example, fread ( ) or write ( ).• RTOSes support asynchronous IOs, for

example, aio_read ( ) and aio_write also in order to not to block a task during the IOs

2008 Chapter-8 L8: "Embedded Systems - Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

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End of Lesson 8 of Chapter 8End of Lesson 8 of Chapter 8