ITEC 352
Lecture 13
ISA(4)
Review
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Binary
Transistors / gates
Circuits
Architecture
Assembly language
High level languages
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Outline
• Assembly in action
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ARC
Registers
• ARC has 32 general purpose registers from r0 to r32
– However, r0 is set to value 0 and cannot be changed.
– We can use all the other registers.
• Using registers is very easy ! Just refer to their contents using the
“%” symbol.
• E.g., Consider the instruction: andcc %r1 %r2 %r3
In English this stands for: “Compute the logical bitwise AND
of the contents of register r1 and register r2 and store in
register r3”
If we don’t use the %, the assembler will return a syntax
error.
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User-Visible
Registers
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PC: program counter, next
Stack Pointer: we will study later.instruction to execute
ARC
Memory
• Using memory is not so straightforward as registers, but is still quite
easy.
– If you enclose a memory location in “[ ]” it refers to the contents of the
memory
– Else it refers to the actual memory location.
• Consider a Java (or C/C++ statement)
int x = 10;
• In ARC, we can allocate this memory as
x: 10
• Now, to access the content of this memory we must enclose “x” in “[
]”
– E.g., Consider the instruction:
ld [x] %r1 // “Load the contents of memory location x in register r1”
• On the other hand, if we do not enclose x within the “[ ]”, then
– With “ld” and “st” instructions you will get a syntax error.
• These instructions require memory content, not data !
– With “call” instruction it will end up calling the actual location of the
memory.
• E.g., call x ; // here it will call the instruction located at memory location “x”
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Summary
so far …
• We looked at:
– ARC instructions
– Using registers
– Using memory.
• Lets look at a few ARC programs on the
simulator and then get our hands dirty into
how the assembly code is actually
represented.
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Example
program
Memory locations are
represented within [ ]
ld and st are the only two
operations allowed on
memory.
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These are information for the
assembler. They are not part of
the assembly language
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.
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ARC Instruction and PSR Formats
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Data Formats
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ARC
Pseudo-Ops
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• 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
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 of the array?
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
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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.
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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).
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Summary
• Assembly programming 101
• Different language, but still within same
paradigm
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