hardware interrupts software interrupts

Size: px

Start display at page:

Download "hardware interrupts software interrupts"

Anne Booker
5 years ago
Views:

1 CS 5212Operating Systems wk 4

2 Interrupts An interrupt is a signal received by the CPU that causes a temporary halt in the execution of a program while some other task is performed. Interrupts may be generated by an input or output device, or by a software routine. After the computer has completed the task to which it was diverted, control returns to the original program.

3 Interrupt types: There are two types of interrupts: hardware interrupts, are a signal to the system from an event that has originated in hardware, such as the pressing of a key on the keyboard, or movement of the mouse. Hardware interrupts are asynchronous. Interrupt signals initiated by programs are called software interrupts. A software interrupt is also called a trap or an exception and is an interrupt generated within a processor by executing an instruction.

4 Software interrupts When it receives a software interrupt signal, the CPU may temporarily switch control to an interrupt handler routine, and the process (i.e. a running instance of a program) in the kernel that was suspended by the interrupt will be resumed after the interrupt has been accommodated. Each type of software interrupt is associated with an interrupt handler, which is a software routine that takes control when the interrupt occurs.

5 Software Interrupts Software interrupts are usually implemented as instructions in the instruction set, which cause a context switch to an interrupt handler similar to a hardware interrupt. Interrupts are a commonly used technique for computer multitasking, especially in real-time computing. Such a system is said to be interrupt-driven.

6 Software Interrupts Software interrupts are synchronous interrupts. They only arrive after the execution of an instruction. They occur at the request of the programmer and can be used to implement system calls.

7 File Descriptors RKELLY

8 Defining File Descriptors File Descriptor is an abstract key for accessing a file Index for an entry in kernel containing details of all open files»a file descriptor is an abstract value of type Unix.file_descr,»containing information necessary to use a file: a pointer to the file, the access rights,»the access modes (read or write), the current position in the file, etc. POSIX- File Descriptor Microsoft File Handle A file descriptor is a handle created by a process when a file is opened There is a limit to the amount of file descriptors per process For Solaris, the default is 64 file descriptors per process

9 How a File Descriptor Works 1 ) When a program opens a file, the operating system returns a corresponding file descriptor. 2 ) The program refers to this file descriptor in order to process the file. 3 ) User Application passes the abstract key to the Kernel via System Call 4 ) Based on the key, the kernel accesses the file on behalf of the application

10 Advantages of File Descriptors Can access a suite of low-level file operations Enable us to gain greater control of files & their data File descriptors are integers starting at 0 that index an array of file information within a process

11 File Descriptors Explained Linux provides each program that is run on it access to three important files. They are standard input, standard output and standard error. And each of these special files (standard input, output and error) have got the file descriptors 0, 1 and 2 respectively. Integer value Name Standard Input (stdin) Standard Output (stdout) Standard Error (stderr)

12 Understanding File Descriptors A file descriptor is a low positive integer. The first three file descriptors (0,1, and 2,) are associated with : standard input (stdin), standard output (stdout) standard error (stderr) For example: Thus, the function scanf() uses stdin and the function printf() uses stdout. You can override the default setting & re-direct the process's I/O to different files by using different file descriptors:

13 Summary File Descriptor is an abstract key for accessing a file File Descriptors are integers starting at 0 that index an array of file information within a process The first three file descriptors (0,1, and 2,) are associated with : standard input (stdin), standard output (stdout) standard error (stderr) Can access a suite of low-level file operations so very useful

14 System Stack ID : NAME : Bin Sun

15 System Stack - outline Define Structure Functions Size & overflow

16 System Stack - Define The system stack is used to store information about subroutine calls. It is to keep track of the point to which each active subroutine should return control when it finishes executing.

17 System Stack - Structure LIFO: Last In, First Out. The caller pushes the return address onto the stack, and the called subroutine, when it finishes, pops the return address off the call stack (and transfers control to that address).

18 System Stack - Structure

19 System Stack - Functions Storing the return address Local data storage Parameter passing Evaluation stack Pointer to current instance Enclosing subroutine context Other return state

20 System Stack - Size & overflow default value : 256 words If the system stack overflows, a stack overflow trap is generated. This signals that the system stack is too small.

CS 201. Exceptions and Processes. Gerson Robboy Portland State University

CS 201. Exceptions and Processes. Gerson Robboy Portland State University CS 201 Exceptions and Processes Gerson Robboy Portland State University Control Flow Computers Do One Thing From startup to shutdown, a CPU reads and executes (interprets) a sequence of instructions, one