Lecture 14

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ITEC 352
Lecture 14
ISA(5)
Review
• Questions?
• Exam 1 next Friday
• Assembly
– Assembler
– Basic structure
– Registers
– Memory
ISA(5)
Outline
• More assembly
– Instructions
• Structure
• Usage
– Intro to loops
• Textbook link
– http://www.mrkay.org/zenpc/ARCHMAN/
ISA(5)
Instruction
Format
• Every ARC instruction is 32 bits in length.
– For instance, the instruction below must fit within 32 bits when
represented in binary.
– To do this, ARC enforces certain formats that allow us to use the
32 bits in different ways.
• These are called instruction formats.
– A format defines how the various bit fields of an instruction are
laid out within 32 bits and how it is interpreted by the ARC
control unit.
ISA(5)
ARC Instruction and PSR Formats
ISA(5)
PSR
• A register that is used to store results of
instructions
• Not values
• If a result is 0
• If a result is negative
• Carry bit (c)
• Overflow bit (v)
ISA(5)
Data Formats
ISA(5)
ARC
Pseudo-Ops
ISA(5)
• Pseudo-ops are instructions
to the assembler. They are
not part of the ISA.
Adding 5
integers …
.org 3000
a: 10
25
2
3
4
Variables for the program a_start: 3000
counter: 0
output: 0
ld [a_start], %r1 ! Load the starting address of a into %r1
ld [counter], %r2 ! Register r2 is the counter.
andcc %r3,%r0, %r3 ! What does this do?
loop: subcc %r2, 5, %r0 ! Have we reached the end ?
be
done ! If %r2 – 5 = 0, exit loop.
addcc %r2, 1, %r2 ! Increment counter
ld %r1, %r4 ! Load the number from the array
addcc %r4, %r3, %r3 ! Accumulate sum into %r3.
addcc %r1, 4, %r1 ! Goto next address
ba loop
done:
st %r3, [output]
jmpl %r15+4, %r0
ISA(5)
Summary
Storage location for
address of the array a.
Having this location
allows us to load the
address “3000” into a
register.
Length is being used as a
“counter” to determine when
to end the loop.
ISA(5)
Other ARC
instructions
• Software traps:
– Allows programs to invoke services from the
OS/hardware, e.g., reading a keyboard or
writing onto a display.
– ARC has trap instructions – but they do not
control the OS/hardware (due to JVM
limitations).
ISA(5)
Summary
• Assembly programming 101
• Different language, but still within same
paradigm
ISA(5)
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