Chapter  L Embedded Systems Architecture Programming and Design  Raj Kamal Publs
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Chapter L Embedded Systems Architecture Programming and Design Raj Kamal Publs

McGraw Hill Inc REAL TIME OPERATING SYSTEMS Lesson 8 IO Subsystems brPage 2br 2008 Chapter 8 L8 Embedded Systems Architecture Programming and Design Raj Kamal Publs McGraw Hill Inc 1 IO Subsystem 1 IO Subsystem brPage 3br 2008 Chapter 8 L8 Embedded

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Chapter L Embedded Systems Architecture Programming and Design Raj Kamal Publs




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Page 1
2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. REAL TIME OPERATING SYSTEMS Lesson 8: I/O Subsystems
Page 2
2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 1. I/O Subsystem 1. I/O Subsystem
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. I/O ports I/O ports z Subsystems of OS device management system UART access sub system and the parallel port access sub

system . z They are used by drivers to communicate with the many devices that use them z I/O instructions depend on the hardware platform. z I/O systems differ in different OSes.
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. z Application z IO Basic functions z IO device driver functions z 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 OS at in an OS
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming

and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 2. I/O Operations 2. I/O Operations
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. z Traditional OSes Synchronous IO operations at a certain fixed data transfer rates. z RTOSes Asynchronous IO operations at the variable data transfer rates. OSes differing IO operations OSes differing IO operations
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. z Are at a certain fixed data

transfer rates. z Therefore, a task (process) blocks tills till completion of the IO. z For example, a write function, write ( ) for 1 kB data transfer to a buffer. Synchronous IO operations Synchronous IO operations
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. Synchronous IO Synchronous IO z Synchronous IO operation means once synchronous IO initiates, the data transfer will block the task till 1 kB data gets transferred to the buffer. z Similarly, read ( ) once initiated blocks the task till 1 kB is read


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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. z Variable data transfer rates. z Permits that a process of high priority to run and should not block during the IOs. Asynchronous IO operations Asynchronous IO operations
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 10 2. POSIX asynchronous functions for 2. POSIX asynchronous functions for IOs IOs
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming

and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 11 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 IOs IOs
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 12 Summary Summary
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal,

Publs.: McGraw Hill, Inc. 13 We learnt We 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
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2008 Chapter 8 L8: "Embedded Systems Architecture, Programming and Design" , Raj Kamal, Publs.: McGraw Hill, Inc. 14 End of Lesson 8 of Chapter 8 End of Lesson 8 of Chapter 8