ceg 320/520: computer organization and assembly language programming1 assembly language programming...
TRANSCRIPT
CEG 320/520: Computer Organization and Assembly Language Programming 1
Assembly Language Programming
Introduction and Addressing Modes
CEG 320/520: Computer Organization and Assembly Language Programming 2
Intro to Assembly Language: Goals
• Introduction to Assembly language– Basic instructions: MOVE, ADD, EXT, etc.– Operand size (B, W, L)– Register Transfer Notation (RTN)
• Addressing Modes– Register direct, immediate, absolute long, register indirect, indexed basic,
autoincrement, autodecrement– When to use the various modes.
• Assigned Reading– HVZ Chapter 2.4, 2.5, 2.6, 3.8, 3.9, 3.10, 3.11– Reference: HVZ Appendix C
CEG 320/520: Computer Organization and Assembly Language Programming 3
Introduction: Basic Instructions
• Instructions begin with a mnemonic which represents the operation to be performed.– MOVE, ADD, SUB, CLR, etc.
• The mnemonic is followed by a character representing the length of the data to be operated on.– Byte (B), Word (W), and Long Word (L)
• In most instructions, the instruction is followed by one or more operands.– How an operand is interpreted depends on the
information provided and the addressing mode used for that operand.
CEG 320/520: Computer Organization and Assembly Language Programming 4
Introduction: A Few Example Instructions
• ADD/SUB/MUL/DIV/AND/OR source, dest– Performs operation on dest and source and stores result in dest.
• NEG location– Computes 2’s complement of value in location, then stores it into location.
• NOT location– Computes complement of value in location, then stores it into location.
• CLR location– Sets value of byte/word/long at location to 0.
• MOVE source, dest– Moves value of source to dest location.
CEG 320/520: Computer Organization and Assembly Language Programming 5
Assembly: Operand size
• Because the 68000 is capable of performing operations on bytes, words and long words:– In 68000 assembly language, a size indicator is appended to
the instruction mnemonic (W=word, B=byte, L=long word):• MOVE.W, MOVE.B, MOVE.L, ADD.W, ADD.B, and ADD.L are
examples of this.
• If the size indicator is omitted, a WORD operation is assumed.
CEG 320/520: Computer Organization and Assembly Language Programming 6
Assembly: Common Instructions - Examples
• MOVE– MOVE.L D1, D2– D2 = D1– Contents of long word in D1 is copied into D2.– Destroys contents of D2!– Contents of D1 do not change!
• ADD/SUB/MUL/DIV– ADD.W D1, D2– D2 = D1 + D2– Sum of words in D1 and D2 is placed into D2.– Destroys contents of D2!
CEG 320/520: Computer Organization and Assembly Language Programming 7
Assembly: Common Instructions - EXT
• EXT.W extends a byte to a word– Bit 7 is copied into bits 8-15.
• EXT.L extends a word into a long word– Bit 15 is copied into bits 16-31
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
CEG 320/520: Computer Organization and Assembly Language Programming 8
Assembly: Common Instructions - EXT
• Sign extension does not change the value of positive or negative 2’s complement numbers!
• 0000 0011 = 3• EXT.L : 0000 0000 0000 0011 = 3
• 1111 1101 = 3• EXT.L : 1111 1111 1111 1101 = 3
CEG 320/520: Computer Organization and Assembly Language Programming 9
Register Transfer Notation: Introduction
• Symbolic and precise way to describe the effect of an instruction.
• Example:MOVE D3,D2The contents of register D3 are copied to register D2.A common notation to designate this is:
D2 [D3] Brackets around D3 indicate “contents of” Left arrow indicates “receives”
CEG 320/520: Computer Organization and Assembly Language Programming 10
Register Transfer Notation: Instructions
• DEST Result
• SUB D5, D7– can be described by:
D7 [D7] - [D5]
• ADD D2, $001004– Here, $001004 is a memory address. The same notation still
suffices:$001004 [$001004] + [D2]
CEG 320/520: Computer Organization and Assembly Language Programming 11
Addressing Modes: Register Direct
MOVE D2, D3
• Register Direct: directly accesses the contents of the indicated register.– RTN:
• D3 [D2]
– Most efficient addressing mode because it requires no memory access to fetch the operand.
– Uses: loop counters, accumulators, operation results of all kinds.
– The data is already in your mailbox, you just need to get it.
CEG 320/520: Computer Organization and Assembly Language Programming 12
Addressing Modes: Register Direct Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2000
MOVE.B D2, D3
Registers
D2 $1234 5678
D3 $XXXX XX78
A0 $0000 2000
MOVE.W D2, D3
Registers
D2 $1234 5678
D3 $XXXX 5678
A0 $0000 2000
Registers
D2 $1234 5678
D3 $1234 5678
A0 $0000 2000
MOVE.L D2, D3
•Register Direct: directly accesses the contents of the indicated register.
CEG 320/520: Computer Organization and Assembly Language Programming 13
Addressing Modes: Absolute Long
MOVE $001020, D2• Absolute Long: accesses the contents of the indicated
memory location.– RTN:
• D2 [$001020]
– Motorola 68k also provides an Absolute Short addressing mode, but we will not be using it.
– Uses: moving stored variables from memory into registers for processing, storing results back to memory.
– You know the actual address ($001020) of the data, so you need to get it from there.
CEG 320/520: Computer Organization and Assembly Language Programming 14
Addressing Modes: Absolute Long Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2000
MOVE.W $002000, D2
Registers
D2 $XXXX 1234
D3 $XXXX XXXX
A0 $0000 2000
MOVE.B $002000, D2
Registers
D2 $XXXX XX12
D3 $XXXX XXXX
A0 $0000 2000
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2000MOVE.L $002000, D2
•Absolute Long: accesses the contents of the indicated memory location.
CEG 320/520: Computer Organization and Assembly Language Programming 15
Addressing Modes: Immediate
MOVE #X, D2• Immediate: an actual number X is provided.
– RTN: • D2 X
– Immediate value is assumed to be decimal unless indicated otherwise (ie by $ for hexadecimal or @ for octal).
– Uses: incrementing loop counters, working with immediate values.
– You know the actual value of the data
CEG 320/520: Computer Organization and Assembly Language Programming 16
Addressing Modes: Immediate Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2000
MOVE.B #12, D2
Registers
D2 $XXXX XX0C
D3 $XXXX XXXX
A0 $0000 2000
MOVE.W #$12, D2
Registers
D2 $XXXX 0012
D3 $XXXX XXXX
A0 $0000 2000
Registers
D2 $0000 000C
D3 $XXXX XXXX
A0 $0000 2000
MOVE.L #12, D2
•Immediate: an actual number X is provided.
CEG 320/520: Computer Organization and Assembly Language Programming 17
Addressing Modes: Register Indirect
MOVE (A0), D2• Register Indirect: accesses the contents of the memory
location in the indicated register. – Effective Address: [A0]
– RTN: • D2 [[A0]]
– Uses: repeated access to the same memory location
– You have a friend (A0) who knows the address of the data. You can ask her where it is in memory, then get it from that location in memory.
CEG 320/520: Computer Organization and Assembly Language Programming 18
Addressing Modes: Register Indirect Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2000
MOVE.B (A0), D2
Registers
D2 $XXXX XX12
D3 $XXXX XXXX
A0 $0000 2000
MOVE.W (A0), D2
Registers
D2 $XXXX 1234
D3 $XXXX XXXX
A0 $0000 2000
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2000
MOVE.L (A0), D2
•Register Indirect: accesses the contents of the memory location in the indicated register.
CEG 320/520: Computer Organization and Assembly Language Programming 19
Addressing Modes: Register Indirect – Indexed Basic
MOVE X(A0), D2• Indexed Basic: An index value X is added to the
memory address in the indicated register to form the effective address, then the contents of the effective address are accessed.– Effective Address:
• [A0] + X
– RTN: • D2 [[A0] + X]
– X is a decimal integer index value– Motorola 68k also provides an Indexed Full addressing mode,
but we will not be using it.
CEG 320/520: Computer Organization and Assembly Language Programming 20
Addressing Modes: Indexed Basic Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2002
MOVE.W 2(A0), D2
Registers
D2 $XXXX ABCD
D3 $XXXX XXXX
A0 $0000 2002
MOVE.W -2(A0), D2
Registers
D2 $XXXX 1234
D3 $XXXX XXXX
A0 $0000 2002
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2002
MOVE.L -2(A0), D2
•Indexed Basic: An index value is added to the memory address to form the effective address.
CEG 320/520: Computer Organization and Assembly Language Programming 21
Addressing Modes: Indexed Basic Example
Struct Student {int grade1;int grade2;int grade3;
};
Struct Student Joe, Bob, Mary;
Avg_Joe = Joe.grade1 + Joe.grade2 + Joe.grade3;
Avg_Joe = Avg_Joe / 3;
MemoryAddress Value$002000 95$002002 89$002004 83
MOVE.L #002000, A0
CLR.L D1
ADD.W (A0), D1
ADD.W 2(A0), D1
ADD.W 4(A0), D1
DIV.W #3, D1
CEG 320/520: Computer Organization and Assembly Language Programming 22
Addressing Modes: Register Indirect – Post-increment
MOVE (A0)+, D2 • Post-increment or Autoincrement: Operand is accessed
indirectly, then address register is incremented.– Effective Address:
• the contents of A0
– RTN: • D2 [[A0]]
• A0 [A0] + the number of bytes accessed
– Increment size: BYTE = 1, WORD = 2, LONG = 4
– Uses: moving through an array, popping from stack
CEG 320/520: Computer Organization and Assembly Language Programming 23
Addressing Modes: Post-increment Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2000
MOVE.B (A0)+, D2
Registers
D2 $XXXX XX12
D3 $XXXX XXXX
A0 $0000 2001
MOVE.W (A0)+, D2
Registers
D2 $XXXX 1234
D3 $XXXX XXXX
A0 $0000 2002
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2004
MOVE.L (A0)+, D2
•Post-increment: Operand is accessed indirectly, then address register is incremented.
CEG 320/520: Computer Organization and Assembly Language Programming 24
Addressing Modes: Register Indirect – Pre-decrement
MOVE.W –(A0), D2• Pre-decrement or Autodecrement: Address register is
decremented, then operand is accessed indirectly.– Effective Address:
• (the contents of A0) – (number of bytes accessed)
– RTN: • A0 [A0] – (number of bytes accessed)
• D2 [[A0]]
– Decrement size: BYTE = 1, WORD = 2, LONG = 4
– Uses: moving through an array, pushing onto stack
CEG 320/520: Computer Organization and Assembly Language Programming 25
Addressing Modes: Pre-decrement Examples
Memory
$002000 $1234
$002002 $5678
$002004 $ABCD
Registers
D2 $XXXX XXXX
D3 $XXXX XXXX
A0 $0000 2004
MOVE.B -(A0), D2
Registers
D2 $XXXX XX78
D3 $XXXX XXXX
A0 $0000 2003
MOVE.W –(A0), D2
Registers
D2 $XXXX 5678
D3 $XXXX XXXX
A0 $0000 2002
Registers
D2 $1234 5678
D3 $XXXX XXXX
A0 $0000 2000
MOVE.L –(A0), D2
•Pre-decrement: Address register is decremented, then operand is accessed indirectly.
CEG 320/520: Computer Organization and Assembly Language Programming 26
Addressing Modes: Post-increment/Pre-decrement
• In the 68000, the increment/decrement depends on the operand size– Suppose A0 = $00002000
– MOVE.B (A0)+,D0 A0 = $00002001
– MOVE.W (A0)+,D0 A0 = $00002002
– MOVE.L (A0)+,D0 A0 = $00002004
CEG 320/520: Computer Organization and Assembly Language Programming 27
Assembly Language: In-Class Exercises
• Assembly Language and Addressing Modes– Exercise
• Big Endian (Memory) vs Little Endian (Registers)– Exercise
CEG 320/520: Computer Organization and Assembly Language Programming 28
Intro to Assembly Language: You Should Know…
• Introduction to Assembly language– Basic instructions: MOVE, ADD, EXT, etc.– Operand size (B, W, L)– Register Transfer Notation
• Addressing Modes– Register direct, immediate, absolute long, register indirect, indexed basic,
autoincrement, autodecrement– When to use the various modes
• Assigned Reading– HVZ Chapter 2.4, 2.5, 2.6, 3.8, 3.9, 3.10, 3.11– Reference: HVZ Appendix C