Lecture 14
ISA(5)

• Questions?
• Exam 1 next Friday
• Assembly
– Assembler
– Basic structure
– Registers
– Memory
ISA(5)

• 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)

ISA(5)

• 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)

ISA(5)

ARC
Pseudo-Ops
ISA(5)
• Pseudo-ops are instructions to the assembler. They are not part of the ISA.

Adding 5 integers …
Variables for the program
.org 3000 a: 10
3
4
25
2 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 ?
done ! If %r2 – 5 = 0, exit loop.
addcc %r2, 1, %r2 ! Increment counter be 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)

• Assembly programming 101
• Different language, but still within same paradigm
ISA(5)