OPERATING SYSTEMS 1 龚玲 lgong@sjtu.edu.cn
OPERATING SYSTEMS 龚玲 lgong@sjtu.edu.cn 1
TODAY'S GOALS o Interrupt o Dual Mode o System Calls vs.APIs o Multiprogramming/Concurrency o http://wenku.baidu.com/course/study/77fldcccda38376ba flfae94#665ea0c7aa00b52acfc7ca94
TODAY’S GOALS Interrupt Dual Mode System Calls vs. APIs Multiprogramming/Concurrency http://wenku.baidu.com/course/study/77f1dcccda38376ba f1fae94#665ea0c7aa00b52acfc7ca94
COMPUTER SYSTEM ORGANIZATION o Computer-system operation One or more CPUs,device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles mouse keyboard printer monitor disks on-line CPU disk controller USB controller graphics adapter memory
COMPUTER SYSTEM ORGANIZATION Computer-system operation One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles
I/O STRUCTURE 0 After I/O starts,control returns to user program only upon I/O completion. Wait instruction idles the CPU until the next interrupt Wait loop (contention for memory access). At most one I/O request is outstanding at a time,no simultaneous I/O processing. o After I/O starts,control returns to user program without waiting for I/O completion. 0 System call-request to the operating system to allow user to wait for I/O completion. Device-status table contains entry for each I/O device indicating its type,address,and state. Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt
I/O STRUCTURE After I/O starts, control returns to user program only upon I/O completion. Wait instruction idles the CPU until the next interrupt Wait loop (contention for memory access). At most one I/O request is outstanding at a time, no simultaneous I/O processing. After I/O starts, control returns to user program without waiting for I/O completion. System call – request to the operating system to allow user to wait for I/O completion. Device-status table contains entry for each I/O device indicating its type, address, and state. Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt
TWO I/O METHODS Synchronous Asynchronous user requesting process requesting process user -waiting一 device driver device driver kernel interrupt handler interrupt handler kernel hardware hardware data transfer data transfer- time time (a) (b)
TWO I/O METHODS Synchronous Asynchronous