TCSS 490A Topics in Computing

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TCSS 490A Topics in Computing Software
SystemsIntroduction to Computer Systems

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What do we want to do tonight ?

• First
• Get acquainted
• Review the syllabus
• Understand the scope, purpose, and expectations
  of the course
• Check out our textbook
• Visit our Laboratory (CP 206C)

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What do we want to do tonight ?

• Second
• Discuss the levels of abstraction involved in a
  computer solution to problem
• Discuss major Numeric Data Types
• Develop expertise in working with various
  numeric bases
• especially base 10, base 2 (binary), and base
  16 (hexidecimal)
• Become proficient converting numbers from one
  base to another
• Become proficient with 2s complement arithmetic
• Understand round off error, sign extension, and
  overflow
• Understand representation of floating point
  numbers
• Understand Binary Logic

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The levels of abstraction involved in a computer
solution to problem

• Problem
• Algorithm
• Language
• Machine Architecture
• Microarchitecture
• Circuits
• Devices
• Electron or light flow

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Develop expertise in working with various numeric
bases

• Base 10
• Base 2 (binary)
• Base 16 (hexidecimal)
• Others ?

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Become proficient converting numbers from one
base to another

• Base 10 to binary
• Binary to Base 10
• Base 10 to Hexidecimal
• Hexidecimal to Base 10
• Binary to Hexidecimal
• Hexidecimal to Binary
• Others ?

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Major Numeric Data Types

• Unsigned Integers
• Signed Integers
• 2s Complement Integers
• Floating Point Numbers

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Become proficient with 2s complement
arithmetic(See Text Figure 2.1)

• Signed Binary Integers
• 1s Complement Binary Integers
• 2s complement Binary Integers

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Binary Arithmetic

• Unsigned add subtract
• 2s complement add subtract

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Understand round off error, sign extension, and
overflow

• overflow
• sign extension
• Binary fractions (the binary point)
• round off error

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Understanding Floating Point NumbersIEEE Standard

• sign (1 bit), exponent (8 bits), fraction (23
  bits)
• (-1)sign x 1.fraction x 2exponent-127
• 1lt exponent lt 254

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ASCII (7 bit or extended)UNICODE (16 bit)

• See ASCII table
• See UNICODE table

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Binary Logic

• NOT
• AND (NAND)
• OR (NOR)
• XOR
• Truth tables
• DeMorgans Theorem

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What do we want to do tonight ?(Second Week)

• Introduce logic circuits
• Relay logic
• MOS semiconductors
• Inverter
• Nor Gate
• Nand Gate
• Combinational Logic
• Decoders
• Full Adder
• PLAs
• MUX Multiplexers

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What do we want to do tonight ?

• Storage Devices
• SR Flip-Flops
• D Latch Flip Flops
• J/K Master Slave Flip Flops
• Registers
• Addressing
• Finite State Machines
• State Diagrams

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The LC-3 as a von Neumann machine
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Data Path of the LC-3
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The Instruction

• FORMAT
• Operation code
• Input Operand(s)
• Output Operand(s)
• ADDRESSING MODES
• Register
• PC-relative
• Base Offset (Base relative)
• Immediate
• Indirect

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Operate Instructions

• Only three operations ADD, AND, NOT
• Source and destination operands are registers

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ADD/AND (Register)
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NOT (Register)
Note Src and Dstcould be the same register.
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ADD/AND (Immediate)
Note Immediate field issign-extended.
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Data Movement Instructions

• Load -- read data from memory to register
• LD PC-relative mode 0010 DR PCoffset9
• LDI indirect mode 1010 DR PCoffset9
• LDR baseoffset mode 0110 DR BaseR offset6
• Store -- write data from register to memory
• ST PC-relative mode 0011 DR PCoffset9
• STI indirect mode 1011 DR PCoffset9
• STR baseoffset mode 0111 DR BaseR offset6
• Load effective address address saved in
  register
• LEA immediate mode 1110 DR PCoffset9

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LD (PC-Relative)
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ST (PC-Relative)
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LDI (Indirect)
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STI (Indirect)
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LDR (BaseOffset)
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STR (BaseOffset)
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LEA (Immediate)
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Branch Instruction

• BR 0000 nzp PCoffset9
• Branch specifies one or more condition codes
• If the set bit is specified, the branch is taken
• PC is set to the address specified in the
  instruction
• Target address is made by adding SEXT(IR80) to
  the PC
• If the branch is not taken - the next
  sequential instruction (PC) is executed.

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BR
/////////////
/////

SEXT
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Jump Instruction

• JMP BaseR 1100 000 BaseR 000000
• Jump is an unconditional branch -- always taken.
• Base
• Address is contents of the register
• Allows any target address.

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TRAP

• Calls a service routine, identified by 8-bit
  trap vector.
• When routine is done, PC is set to the
  instruction following TRAP.

vector routine
x23 input a character from the keyboard
x21 output a character to the monitor
x25 halt the program
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Example 1 Multiply

• This program multiplies two unsignedintegers in
  R4 and R5.

x3200 0101010010100000 x3201 0001010010000100 x320
2 0001101101111111 x3203 0000011111111101 x3204
1111000000100101
R2 lt- 0 R2 lt- R2 R4 R5 lt- R5 1 BRzp
x3201 HALT
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Example
Address Instruction Comments
x30F6 1 1 1 0 0 0 1 1 1 1 1 1 1 1 0 1 R1 ? PC 3 x30F4
x30F7 0 0 0 1 0 1 0 0 0 1 1 0 1 1 1 0 R2 ? R1 14 x3102
x30F8 0 0 1 1 0 1 0 1 1 1 1 1 1 0 1 1 MPC - 5 ? R2Mx30F4 ? x3102
x30F9 0 1 0 1 0 1 0 0 1 0 1 0 0 0 0 0 R2 ? 0
x30FA 0 0 0 1 0 1 0 0 1 0 1 0 0 1 0 1 R2 ? R2 5 5
x30FB 0 1 1 1 0 1 0 0 0 1 0 0 1 1 1 0 MR114 ? R2Mx3102 ? 5
x30FC 1 0 1 0 0 1 1 1 1 1 1 1 0 1 1 1 R3 ? MMx30F4 R3 ? Mx3102 R3 ? 5
Opcode
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Using Branch Instructions

• Compute sum of 12 integers.Numbers start at
  location x3100. Program starts at location x3000.

R1 ? x3100R3 ? 0R2 ? 12
R20?
R4 ? MR1R3 ? R3R4R1 ? R11 R2 ? R2-1
NO
YES
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Sample Program
Address Instruction Comments
x3000 1 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0 R1 ? x3100
x3001 0 1 0 1 0 1 1 0 1 1 1 0 0 0 0 0 R3 ? 0
x3002 0 1 0 1 0 1 0 0 1 0 1 0 0 0 0 0 R2 ? 0
x3003 0 0 0 1 0 1 0 0 1 1 1 0 1 1 0 0 R2 ? 12
x3004 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 1 If Z, goto x3009
x3005 0 1 1 0 1 0 0 0 0 1 0 0 0 0 0 0 Load next value to R4
x3006 0 0 0 1 0 1 1 0 1 1 0 0 0 0 0 1 Add to R3
x3007 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 Increment R1 (pointer)
X3008 0 0 0 1 0 1 0 0 1 0 1 1 1 1 1 1 Decrement R2 (counter)
x3009 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 Goto x3004
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Flow Chart
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Program (1 of 2)
Address Instruction Comments
x3000 0 1 0 1 0 1 0 0 1 0 1 0 0 0 0 0 R2 ? 0 (counter)
x3001 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 0 R3 ? Mx3102 (ptr)
x3002 1 1 1 1 0 0 0 0 0 0 1 0 0 0 1 1 Input to R0 (TRAP x23)
x3003 0 1 1 0 0 0 1 0 1 1 0 0 0 0 0 0 R1 ? MR3
x3004 0 0 0 1 1 0 0 0 0 1 1 1 1 1 0 0 R4 ? R1 4 (EOT)
x3005 0 0 0 0 0 1 0 0 0 0 0 0 1 1 1 0 If Z, goto x300E
x3006 1 0 0 1 0 0 1 0 0 1 1 1 1 1 1 1 R1 ? NOT R1
x3007 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 R1 ? R1 1
X3008 0 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 R1 ? R1 R0
x3009 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 1 If N or P, goto x300B
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Program (2 of 2)
Address Instruction Comments
x300A 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 1 R2 ? R2 1
x300B 0 0 0 1 0 1 1 0 1 1 1 0 0 0 0 1 R3 ? R3 1
x300C 0 1 1 0 0 0 1 0 1 1 0 0 0 0 0 0 R1 ? MR3
x300D 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 Goto x3004
x300E 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1 1 R0 ? Mx3013
x300F 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 R0 ? R0 R2
x3010 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 1 Print R0 (TRAP x21)
x3011 1 1 1 1 0 0 0 0 0 0 1 0 0 1 0 1 HALT (TRAP x25)
X3012 Starting Address of File
x3013 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 ASCII x30 (0)
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Filled arrow info to be processed. Unfilled
arrow control signal.
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Three Basic Constructs

• There are three basic ways to decompose a task

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LC-3 Assembly Language Syntax

• Each line of a program is one of the following
• an instruction
• an assember directive (or pseudo-op)
• a comment
• Whitespace (between symbols) and case are
  ignored.
• Comments (beginning with ) are also ignored.
• An instruction has the following format

LABEL OPCODE OPERANDS COMMENTS
optional
mandatory
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An Assembly Language Program

• Program to multiply a number by the constant 6
• .ORIG x3050
• LD R1, SIX
• LD R2, NUMBER
• AND R3, R3, 0 Clear R3. It will
• contain the product.
• The inner loop
• AGAIN ADD R3, R3, R2
• ADD R1, R1, -1 R1 keeps track of
• BRp AGAIN the iteration.
• HALT
• NUMBER .BLKW 1
• SIX .FILL x0006

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Assembler Directives

• Pseudo-operations
• do not refer to operations executed by program
• used by assembler
• look like instruction, but opcode starts with
  dot

Opcode Operand Meaning
.ORIG address starting address of program
.END end of program
.BLKW n allocate n words of storage
.FILL n allocate one word, initialize with value n
.STRINGZ n-character string allocate n1 locations, initialize w/characters and null terminator
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Trap Codes

• LC-3 assembler provides pseudo-instructions
  foreach trap code, so you dont have to remember
  them.

Code Equivalent Description
HALT TRAP x25 Halt execution and print message to console.
IN TRAP x23 Print prompt on console,read (and echo) one character from keybd.Character stored in R070.
OUT TRAP x21 Write one character (in R070) to console.
GETC TRAP x20 Read one character from keyboard.Character stored in R070.
PUTS TRAP x22 Write null-terminated string to console.Address of string is in R0.
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Sample Program

• Count the occurrences of a character in a
  file.Remember this?

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Char Count in Assembly Language (1 of 3)

• Program to count occurrences of a character in
  a file.
• Character to be input from the keyboard.
• Result to be displayed on the monitor.
• Program only works if no more than 9
  occurrences are found.
• Initialization
• .ORIG x3000
• AND R2, R2, 0 R2 is counter, initially 0
• LD R3, PTR R3 is pointer to characters
• GETC R0 gets character input
• LDR R1, R3, 0 R1 gets first character
• Test character for end of file
• TEST ADD R4, R1, -4 Test for EOT (ASCII x04)
• BRz OUTPUT If done, prepare the output

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Char Count in Assembly Language (2 of 3)

• Test character for match. If a match,
  increment count.
• NOT R1, R1
• ADD R1, R1, R0 If match, R1 xFFFF
• NOT R1, R1 If match, R1 x0000
• BRnp GETCHAR If no match, do not increment
• ADD R2, R2, 1
• Get next character from file.
• GETCHAR ADD R3, R3, 1 Point to next character.
• LDR R1, R3, 0 R1 gets next char to test
• BRnzp TEST
• Output the count.
• OUTPUT LD R0, ASCII Load the ASCII template
• ADD R0, R0, R2 Covert binary count to ASCII

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Char Count in Assembly Language (3 of 3)

• Storage for pointer and ASCII template
• ASCII .FILL x0030
• PTR .FILL x4000
• .END

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Program to find number of negative numbers

• 1. Initialize Registers
• 2. Get next data
• 3. If sign is negative, increment count
• 4. Update data pointer
• 5. If not done, go to 2.
• 6. Store result
• 7. Halt

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Program to find number of negative numbers

• Initialize Registers
• R0 Counter of neg numbers
• R1 Sign Mask
• R2 Number of Data words
• R3 Ptr to Data
• R4 Data buffer
• 2. Get next data
• Load R4 with (R3)
• 3. If sign is negative, increment count
• AND Sign Mask with Data, Inc R0 if not
  zero
• 4. Update data pointer
• Inc R3
• Dec R2
• 5. If not done, go to 2.
• IF Positive go to 2.

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Program to find number of negative numbers

• .ORIG x3000
• Initialze Registers
• AND R0, R0, 0 Clr counter of negative numbers
• LD R1, MASK Set sign bit mask
• ADD R2, R0, 10 Set of Data words
• LD R3, PTR_DATA Set Data Ptr
• Loop to check words
• LOOP LDR R4, R3, 0 Fetch data word
• AND R4, R4, R1 Test for sign bit
• BRz NEXT
• ADD R0, R0, 1 Inc counter if negative
• NEXT ADD R3, R3, 1 Inc Data Ptr
• ADD R2, R2, -1 Dec of Data words left
• BRp LOOP

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Assembly Language Instructions

• Move data Instructions
• Reg ? Reg ADD, AND
• Reg ? Memory LD, LDR, LDI
• Memory ? Reg ST, STR, STI
• Clear REG AND
• LOAD ADDRESS LEA
• Computation Arithmetic and Logic
• Arithmetic ADD
• LOGIC AND, NOT, (SHIFT)
• Program Control support IF, WHEN, DO
• BR
• JMP
• Subroutines ( Methods) - Pass Parameters by
  value, by reference,
• Stack
• JSR
• JSRR

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Addressing

• Register operand is in a register
• Immediate (or literal) operand is in IR50
• PC Relative operand is in PCIR80ext or
  PCIR100ext
• Base Offset operand is in BaseReg or
  BaseRegIR50
• Indirect operand address is at PCIR80

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Hardware

• Arithmetic and Logic Unit Nominally 2 operands
• Memory - Memory Address Register (MAR) Memory
  Data Register (MDR)
• Registers (R0-R7) Convention R0, R5, R6, R7
• Program Counter (PC) Incremented after
  instruction fetch!
• Instruction Register (IR) Hold Instruction
  being executed
• Processor Status Register (PSR) Privileged,
  Priority, CCs
• 6) Stack Pointer Storage Regs Saved.SysStackPtr
  Saved.UserStackPtr

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Traps

• Execute TRAP vector - Operating System
  Service Routines
• 2) Trap Vectors are at memory locations
  000000FF
• Trap Vectors contain addresses of Trap Service
  Routines
• (PC) is loaded into R7
• Address of Trap Service Routine loaded into PC
• Service Routine Program executed
• Trap service routine program ends with an RET
• ( (R7) loaded into PC)

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Subroutines

• Execute JSR or JSRR - Call Subroutine or
  Method
• 2) Location of Subroutine is in the Instruction
• (PC) stored in R7
• Address from JSR or JSRR is loaded into PC
• Subroutine is executed
• R0 possibly contains passed parameter (or
  address)
• Stack may contain passed parameters (or
  addresses)
• R5 may be used to return error message
• Ro possibly contains return parameter (or
  address)
• Stack may contain return parameters (or
  addresses)
• Subroutine program ends with an RET
• ( (R7 loaded into PC)

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Interrupts

• Enable Interrupts by setting intr enable bit in
  Device Status Reg
• 2) When device ready bit is set and the priority
  is higher than the priority of the presently
  running program (and execution of an instruction
  is complete) the processor initiates the
  interrupt
• The Processor saves the state of the program
• The Processor goes into Privileged Mode
• PSR bit 15 cleared
• Priority level is set (likely established by
  the interrupting device)
• The CCs are cleared
• (R6) is stored in USP.saved register
• The Supervisor Stack Ptr is loaded into R6
• The (PC) and the (PSR) are PUSHED onto the
  Supervisor Stack
• The contents of the other registers are not
  saved. Why?
• The Processor Loads the PC from the Interrupt
  vector (vectors in 1001FF)
• Interrupt Service Routine is executed
• Ends with an RTI

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Higher Level Languages

• High Level Languages give us
• Symbolic Names
• Expressions
• Libraries of functions/subroutines
• Abstraction of underlying hardware
• Readability
• Structure help keep bugs out

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First C Program

• /
• Program Name countdown, our first C program
  
• 
  
• Description This program prompts the user
  to type in
• a positive number and counts down from that
  number to 0,
• displaying each number along the way.
  
• /
• / The next two lines are preprocessor directives
  /
• include ltstdio.hgt
• define STOP 0
• / Function main
  /
• / Description prompt for input, then display
  countdown /
• int main()
• / Variable declarations /

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Compiling C
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Terms

• Pre processor directives
• define
• include
• Header Files
• ltstdio.hgt
• Data Types
• int
• char
• double
• Scope
• Local
• Global
• Variable initiation

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Scope

• include ltstdio.hgt
• int globalVar 2 / This variable is
  global /
• int main()
• int localVar 3 / This variable is local
  to main /
• printf("Global d Local d\n", globalVar,
  localVar)
• int localVar 4 / Local to this
  sub-block /
• printf("Global d Local d\n", globalVar,
  localVar)
• printf("Global d Local d\n", globalVar,
  localVar)
• return 0

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Another program

• include ltstdio.hgt
• int main()
• int amount / The number of bytes to be
  transferred /
• int rate / The average network transfer
  rate /
• int time / The time, in seconds, for the
  transfer /
• int hours / The number of hours for the
  transfer /
• int minutes / The number of mins for the
  transfer /
• int seconds / The number of secs for the
  transfer /
• / Get input number of bytes and network
  transfer rate /
• printf("How many bytes of data to be
  transferred? ")
• scanf("d", amount)
• printf("What is the transfer rate (in
  bytes/sec)? ")
• scanf("d", rate)

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Another program

• / Include the standard I/O header file /
• include ltstdio.hgt
• int inGlobal / inGlobal is a global variable
  because /
• / it is declared outside of all
  blocks /
• int main()
• int inLocal / inLocal, outLocalA, outLocalB
  are all /
• int outLocalA / local to main
  /
• int outLocalB
• / Initialize /
• inLocal 5
• inGlobal 3
• / Perform calculations /
• outLocalA inLocal inGlobal
• outLocalB (inLocal inGlobal) - (inLocal -
  inGlobal)

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Another program

• include ltstdio.hgt
• define RADIUS 15.0 / This value is in
  centimeters /
• int main()
• const double pi 3.14159
• double area
• double circumference
• / Calculations /
• area pi RADIUS RADIUS / area
  pir2 /
• circumference 2 pi RADIUS /
  circumference /
• /
  2pir /
• printf("Area of a circle with radius f cm is
  f cm2\n",
• RADIUS, area)
• printf("Circumference of the circle is f
  cm\n",

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Another program

• int main()
• char nextChar / Next character in email
  address /
• int gotAt FALSE / Indicates if At _at_ was
  found /
• int gotDot FALSE / Indicates if Dot . was
  found /
• printf("Enter your email address ")
• do
• scanf("c", nextChar)
• if (nextChar '_at_')
• gotAt TRUE
• if (nextChar '.' gotAt TRUE)
• gotDot TRUE
• while (nextChar ! ' ' nextChar ! '\n')

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Another program

• include ltstdio.hgt
• define FALSE 0
• define TRUE 1
• int main()
• char nextChar / Next character in email
  address /
• int gotAt FALSE / Indicates if At _at_ was
  found /
• int gotDot FALSE / Indicates if Dot . was
  found /
• printf("Enter your email address ")
• do
• scanf("c", nextChar)
• if (nextChar '_at_')
• gotAt TRUE
• if (nextChar '.' gotAt TRUE)
• gotDot TRUE
• while (nextChar ! ' ' nextChar ! '\n')

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Another program

• include ltstdio.hgt
• define FALSE 0
• define TRUE 1
• int main()
• char nextChar / Next character in email
  address /
• int gotAt FALSE / Indicates if At _at_ was
  found /
• int gotDot FALSE / Indicates if Dot . was
  found /
• printf("Enter your email address ")
• do
• scanf("c", nextChar)
• if (nextChar '_at_')
• gotAt TRUE
• if (nextChar '.' gotAt TRUE)
• gotDot TRUE
• while (nextChar ! ' ' nextChar ! '\n')

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Another program

• Program to compute z x Y
• (R5) -gt X , (R5)-1 -gt Y
• AND R0, R0, 0 RO lt 0
• LDR R1, R5, 0 load value of x
• LDR R2, R5, -1 load value of y
• BRz DONE if y is zero, we're done
• BRp LOOP if y is positive, start mult
• y is negative
• NOT R1, R1
• ADD R1, R1, 1 R1 lt -x
• NOT R2, R2
• ADD R2, R2, 1 R2 lt -y (-y is positive)
• LOOP ADD R0, R0, R1 Multiply loop
• ADD R2, R2, -1 The result is in R2