CS 162 Nachos Tutorial Image courtesy of Thomas Andersen http www cs washington edu homes tom nachos Outline What is Nachos Capabilities purpose history How does it work What am I supposed to do The 4 phases How do I get started What is Nachos An instructional operating system Includes many facets of a real OS Threads Interrupts Virtual Memory I O driven by interrupts You can and will modify and extend it What else is Nachos Nachos also contains some hardware simulation MIPS processor Can handle MIPS code in standard COFF except for floating point instructions You can and will write code in C compile it to MIPS and run it on Nachos Console Network interface Timer Why Nachos What better way to learn how an OS works than by building one Much easier and more reasonable to build a simulated OS in Java Skeleton code allows us to work on replace or upgrade one piece at a time Why Java Java much simpler than C Java is type safe can t write off the end of an array easier to debug Much easier and more reasonable to machine grade a Java project More portable History of Nachos Originally created here at Berkeley in 1992 in C and a little assembly By Wayne A Christopher Steven J Procter and Thomas E Anderson Used at many universities Rewritten in Java by Daniel Hettena Now simpler easier to grade type safe portable and more students now know Java How does Nachos work Entirely written in Java Broken into Java packages nachos ag autograder classes nachos machine most of the action nachos network Phase 4 nachos security tracks priviledge nachos threads Phase 1 nachos userprog Phase 2 nachos vm Phase 3 Nachos Architecture Nachos Nachos Kernel User Program User Program Simulated HW JVM Real OS Hardware Booting Nachos When you run Nachos it starts in nachos machine Machine main Machine main initializes devices interrupt controller timer MIPS processor console file system Passes control to the autograder AutoGrader will create a kernel and start it this starts the OS The Machine nachos machine Machine Kicks off the system and provides access to various hardware devices Machine interrupt Machine timer Machine console Machine networkLink Interrupt Controller Kicks off hardware interrupts nachos machine Interrupt class maintains an event queue clock Clock ticks under two conditions One tick for executing a MIPS instruction Ten ticks for re enabling interrupts After any tick Interrupt checks for pending interrupts and runs them Calls device event handler not software interrupt handler Interrupt Controller cont Important methods accessible to other hardware simulation devices schedule takes a time handler tick takes a boolean 1 or 10 ticks checkIfDue invokes due interrupts enable disable All hardware devices depend on interrupts they don t get threads Timer nachos machine Timer Hardware device causes interrupts about every 500 ticks not exact Important methods getTime tells many ticks so far setInterruptHandler tells the timer what to do when it goes off Provides preemption Serial Console Java interface nachos machine SerialConsole Contains methods readByte returns one byte or 1 and waits to interrupt when it has more writeByte takes one byte and waits to interrupt when its ready for more setInterruptHandlers tells the console who to call when it receives data or finishes sending data Normally implemented by nachos machine StandardConsole hooked up to stdin and stdout Schedules read event every Stats ConsoleTime ticks to polls stdin invokes interrupt handler Other Hardware Devices Disk Didn t make the jump to Java from C we don t use it for our Nachos assignments Network Link Similar to console but packet based Used for Phase 4 You should be able to figure it out by then The Kernel Abstract class nachos machine Kernel Important methods initialize initializes the kernel duh selfTest performs test not used by ag run runs any user code none for 1st phase terminate Game over Never returns Each Phase will have its own Kernel subclass Threading Happens in package nachos threads All Nachos threads are instances of nachos thread KThread or subclass KThread has status New Ready Running Blocked Finished Every KThread also has a nachos machine TCB Internally implemented by Java threads Running threads Create a java lang Runnable make a Kthread and call fork Example class Sprinter implements Runnable public void run run real fast Sprinter s new Sprinter new KThread s fork Scheduler Some subclass of nachos machine Scheduler Creates ThreadQueue objects which decide what thread to run next Defaults to RoundRobinScheduler Specified in Nachos configuration file Nachos Configuration nachos conf file lets you specify many options which classes to use for Kernel Scheduler whether to be able to run user progs etc Different one for each project Creating the First Thread ThreadedKernel initialize public void initialize String start threading new KThread null What does KThread perform What thread does it create args Advanced Topics The simulated MIPS processor Address translation User level process Syscalls and exception handling You will get to know more when we get there How are we using it Four Nachos assignments Phases Phase 1 Threading Phase 2 Multiprogramming Phase 3 Caching and Virtual Memory Phase 4 Networks and Distributed Systems Nachos Projects Extend Embrace Nachos Add features to Nachos kernel code Threading File system calls Implement user programs in C 4 Phases Phase 1 Thread system due 2005 02 16 Phase 2 Multiprogramming due 2005 03 07 Phase 3 Caching Virtual Memory due 2005 03 30 Phase 4 Networks Distributed Systems due 2005 04 21 Phase 1 Threading 5 KThread join 5 Condition Variables more efficiently 10 Alarm 20 Communicator 35 PriorityScheduler 25 Rowing Hawaiian kids Row boat synchronization Get Adults and Children from Oahu to Molokai Constraints 1 boat Boat fits 1 child or 2 children or 1 adult Pilot required Phase 2 Multiprogramming 30 File system calls creat open read write close unlink 25 Multiprogramming Multiple users programs at once 30 System calls exec join exit 15 LotteryScheduler Phase 3 Caching VM 30 Implement TLB Inverted page table 40 Paged virtual memory Fit large program s in memory 30 Lazy loading Don t load parts of program until needed Phase 4 Networking 75 Networking syscalls Connect accept 25 Chat program Like IRC Workload grading percentages given Divide work fairly Projects depend on each other E g LotteryScheduler in next project depends on PriorityScheduler How to get started Go
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