© 2009, D. J. Foreman 1 Computer Organization

© 2009, 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

© 2009, D. J. Foreman 3 Timing  Cycle – timing in a computer comes from a master clock controlled by a crystal oscillator  Clock ticks (million 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*1 / 10 6 =.1 µsec = seconds  Terms ■ Giga = 10 9 and nano = ■ Mega = 10 6 and micro = 10 -6

© 2009, D. J. Foreman 4 Storage Speed Hierarchy  On the Motherboard ■ CPU Registers – extremely fast ■ Cache (CPU Internal) – very fast ■ Cache (External) – fast ■ Main Memory - slow  External ■ Flash disk – 0 latency ■ Magnetic Disks – high latency ■ Optical Disk – very high latency ■ Magnetic Tapes – seq'l, extremely high latency

© 2009, D. J. Foreman 5 Instruction Processing 1. Fetch – get instruction from RAM 2. Decode - h/w determines operation from bit pattern of first (or more) byte(s) 3. Obtain operand data ■ From Registers or RAM ■ Into ALU 4. Execute (perform the operation) 5. Store results back to RAM 6. Update Instruction Counter ■ (sometimes called Program Counter)

© 2009, D. J. Foreman 6 Device-Controller/Software Relationship Application API O/S Device driver Device controller Device S/W H/W

© 2009, D. J. Foreman 7 Device Controller Interface  Data width  Commands ■ Read ■ Write ■ Seek  Status codes ■ Busy ■ Error ■ Done ■ Ready

© 2009, D. J. Foreman 8 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 (explore: 1 per device) Turned on by device controller Turned off by O/S No "race" conditions

© 2009, D. J. Foreman 9 Interrupt Handling Sequence  Controller (atomic action) ■ turns on flag ■ Sets code indicating which device  H/W (atomic action) ■ Switches to privileged mode ■ interrupts off ■ Memory protection off ■ Sets IC to general interrupt handler in O/S  O/S ■ Saves registers (NOT part of atomic actions)

© 2009, D. J. Foreman 10 Kernel S/W Interrupt Handling  Save (uses multiple machine cycles) ■ Registers ■ Stack  Determine interrupt cause ■ I/O, error, service request, external signal  Jump to proper interrupt-handler

© 2009, D. J. Foreman 11 Kernel Returns to the User  Restores user's state & values ■ User mode (kernel/user) ■ Registers ■ Stack  Load IC with interrupts enabled Allows new interrupt before switching (return to processing on previous slide)

© 2009, D. J. Foreman 12 Trap or System Call Instruction  Atomic operation ■ Causes an interrupt (type=service request) ■ It is NOT a “call” as if to a function  Common service request handler ■ Uses code to select address in trap table ■ Trap table contains addresses of specific programs for specific request

© 2009, D. J. Foreman 13 Traps or Kernel “Calls”  Examples ■ cout << x; ■ seek (device, position); ■ X=ftime();  User functions expand into assembly code for a "trap" or "svc" instruction  "trap" causes a H/W switch to the kernel  Kernel performs op and returns to user

© 2009, D. J. Foreman 14 System call example fork (My_fork_loc); {● ● trap (K_FORK, *My_fork_loc); } My_fork_loc:…; *Do_fork Do_fork(loc) { ● ● start_process (loc); mode=0; return; } Trap table *Do_fork User spaceKernel space K_fork is entry # for "FORK" Kernel space

© 2009, D. J. Foreman 15 Instruction Processing with Interrupts fetchexecute Interrupts allowed? No yes previous inst Interrupt pending? No process interrupt yes

© 2009, D. J. Foreman 16 Direct Memory Addressing (DMA)  Allows device controller to access RAM w/o going through the CPU  Increases throughput  Reduces interrupt handling

© 2009, D. J. Foreman 17 Device addressing  Two methods shown in text: ■ Conventional External to RAM Limited only by size of device address ■ Memory-mapped devices Uses 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)

© 2009, D. J. Foreman 18 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

© 2009, D. J. Foreman 19 Pipelined Instructions FetchDecodeExecute Store Fetch Decode Execute Store FetchDecodeExecuteStore Done t1, etct0

© 2009, D. J. Foreman 20 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

Hex addressIBM z/390 memory content 0IPL PSW or Restart PSW 8IPL CCW1 or Restart old PSW 10IPL CCW2 18External Old PSW 20Supervisor Call Old PSW 28Program Check Old PSW 30Machine Check Old PSW 38I/O Old PSW 58External New PSW 60Supervisor Call New PSW 68Program Check New PSW 70Machine Check New PSW 78I/O New PSW 80External interrupt data 88 (4 bytes)SVC interruption data: 13-14= ILC, 16-31= interruption code (SVC #) paired © 2009, D. J. Foreman 21

© 2009, D. J. Foreman 22 PC-bootable disk layout 0x00-0x02 jump inst to 0x1e 0x03-0x0aPC manufacturer name 0x0b-0x0csectors/cluster 0x0d-0x0freserved for boot record 0x10-0x10# of FAT's 0x11-0x12# root directory entries 0x13-0x14# logical sectors 0x15-0x15media descriptor 0x16-0x17sectors/FAT 0x18-0x19sectors/track 0x1a-0x10b # surfaces (heads) 0x1c-0x1d# hidden sectors 0x1e-…boot program