© 2004, D. J. Foreman 1 Computer Organization

© 2004, D. J. Foreman 2 Basic Architecture Review  Von Neumann ■ Distinct single-ALU & single-Control ■ Fixed circuitry  Non-von Neumann ■ Various changes Multiple ALUs Merged ALU and Control Alternatives to ALU

© 2004, D. J. Foreman 3 Timing  Cycle – timing in a computer comes from a master clock controlled by a crystal oscillator  Clock ticks (billion cycles / sec)  Frequency = 1/period and Period = 1/frequency  Let’s use 10 MHz to make the arithmetic easier ■ 10 MHz = 10 x 10 6 Hz = 10 7 Hz ■ Period is 1 / 10 7 = seconds  Terms ■ Giga = 10 9 and nano = ■ Mega = 10 6 and micro = 10 -6

© 2004, D. J. Foreman 4 Storage Speed Hierarchy  CPU Registers – internal to CPU  Cache (CPU Internal) – very high speed  Cache (External) – high speed  Main Memory - slow  Electronic (SSD) – 0 latency  Magnetic Disks – high latency  Optical Disk – very high latency  Magnetic Tapes – seq'l, very high latency

Machine State Management  State vector (Program Status Word) ■ Interruptability ■ Memory protection ■ Privilege mode ■ Instruction counter ■ Misc. (arch dependent)  Reserved (arch. defined) storage areas © 2004, D. J. Foreman 5

6 Operation  Fetch – get instruction from RAM  Decode- h/w determines operation from bit pattern of first (or more) byte(s)  Obtain operand data ■ From Registers or RAM ■ Into ALU  Execute (perform the operation)  Store results back to RAM  Update Instruction Counter ■ (sometimes called Program Counter)

© 2004, D. J. Foreman 7 Device-Controller-Software Relationship Application API O/S Device driver Device controller Device S/W H/W

© 2004, D. J. Foreman 8 Device Controller Interface  Data width  Commands ■ Read ■ Write ■ Seek  Status codes ■ Busy ■ Error ■ Done ■ Ready

© 2004, D. J. Foreman 9 I/O Operations  Controller manages device  Devices are MUCH slower than CPU  CPU can process while device runs  Need to know when done ■ Polling (continual testing for "done") ■ Special h/w for notification – interrupt flag One bit in CPU Turned on by device controller Turned off by O/S No "race" conditions

Control Flow  Hardware (I/O or SVC) raises voltage on an interrupt line ■ Current PSW saved to reserved RAM area ■ "interrupt PSW" becomes "current PSW" ■ Machine state set, IC set  OS is now running at primary interrupt handler  All registers have user data, must save (if not done by hw) to reserved RAM  Load register ->PCB list  Find user who was running  Save registers into his PCB © 2004, D. J. Foreman 10

© 2004, D. J. Foreman 11 Interrupt Handling Sequence  Controller (atomic action) ■ turns on flag & sets code indicating device  H/W (atomic action) ■ Switches to privileged mode ■ Turns interrupts off ■ Turns full memory protect off ■ Sets IC to interrupt handler in O/S  O/S ■ Interrupt handler executes ■ Returns to application in user mode

© 2004, D. J. Foreman 12 Interrupt Handler  Saves user state (vs. machine state) ■ Registers ■ Stack pointer ■ IC  Switches to device-handler  Restores user's state  Returns to user with interrupts enabled  Might NOT be atomic Allows new interrupt before switching

© 2004, D. J. Foreman 13 Trap or Supervisor Call Instruction  Atomic operation ■ Switches to privileged mode ■ Sets IC to common interrupt handler in O/S ■ Contains code for specific request  Common handler ■ Uses code to select address in trap table ■ Trap table contains addresses of specific programs

© 2004, D. J. Foreman 14 Instruction Processing with Interrupts fetchexecute Interrupts allowed? No yes previous inst pending? No process interrupt yes

© 2004, D. J. Foreman 15 Direct Memory Addressing  Allows device controller to get/put RAM w/o going through the CPU  Increases throughput  Reduces interrupt handling

© 2004, D. J. Foreman 16 Device addressing  Two methods shown in text: ■ Conventional External to RAM Limited only by size of address ■ Memory-mapped devices Use reserved part of RAM Limited by reserved space  Third method – used in some mainframes ■ Channels – addresses 00-0f (1 byte) ■ Sub-channels – addresses 00-ff (2 nd byte) ■ Total of 4096 independent devices (0000-0fff)

© 2004, D. J. Foreman 17 Loader Processing  Find the executable file  Resolve relative addresses within program to actual locations  Connect DLL's to procedure call structure ■ Shared collection of programs & entry points

© 2004, D. J. Foreman 18 Pipelined Instructions FetchDecodeExecute Store Fetch Decode Execute Store Fetch Decode Execute Store Done

© 2004, D. J. Foreman 19 Software, Firmware, Hardware  Software ■ Programs you can install/remove/transport to another computer which are stored on disk, CD, etc and run from within RAM  Firmware ■ Programs usually installed only by chip maker and which run from within ROM ■ May be upgraded by user (depends on chip)  Hardware ■ The physical components of the system