1. Cosc 2150: Computer Organization
ARC assembly code
Simplified SPARC language 1

2. There are 32 32-bit registers. %r0 through %r31. Reserved registers:
ARC Hardware
There are bit registers. %r0 through %r31.
Reserved registers:
%r0 is always 0.
Storing anything in %r0 will be lost.
%r14 is a stack pointer register
also called %sp
%r15 is link register (used for subroutine calls) 2

3. The ARCTools Simulator Window

4. There are two addition registers
%pc, a 32-bit program counter register
%psr, which is a processor status register Where arithmetic/logic flags are set.
They are N,Z,V,C,
where N is a negative flag
Z is the zero flag
V is the overflow flag
C is the carry flag.
The lowest 211 = 2048 addresses of the memory map are reserved for use by the operating system. 4

5. A Basic ARC assembly program
.begin
.org 2048 !Lowest space in memory a program can go
main: !special label, for start of your code
!Assembly instructions
halt !end of assembly code
var: value ! variable: value of the variable.
.end 5

6. Arithmetic instructions
All arithmetic and logic instructions have 3 opcode: instruction op1, op2, op3.
Only op2 can be immediate load/ number otherwise, they will refer to a register.
Any instructions that end in a cc, set condition codes (NZVC)
addcc %r0, 1, %r1
(%r1 = 0 + 1) would set N=0, Z=0, V=0, and C=0
subcc %r0, 1, %r1
(%r1 = 0 – 1) would set N=1, Z=0, V=1, and C=0
Assuming %r1 = 1, subcc %r1, 1, %r1
(%r1 = %r1 –1), would set N=0, Z=1, V=0, and C=0 6

7. Data transfer instructions
All have 2 opcode instructions.
load:
ld [x], %r1 !load the value of x into %r1
ld %r1+x, %r2 !load the value found by %r1 +x (offset) into %r2
store:
st %r1, [x] !store the value of %r1 into x
st %r2, %r1+x ! store the value of %r2 into the address %r1 +x 7

8. Branch instructions
All but one branch instruction have a single opcode in the following format
branch label ! branch conditionally or unconditionally to the label
example:
ba done !branch to the label done
! assembly code
done: halt ! stop the program
be, bcs, bcc, bneg, bvs, bvc, bne, bpos all use the NZVC condition flags to as the condition whether to branch or not.
jmpl and call are used for subroutines, which will be covered later. 8

9. The ARCTools Edit Window

10. The ARCTools Edit Window
• The Edit window with an asm file and the file dialog

11. Assembly
The arc4 program after assembly, showing arc4.lst, the listing file.

12. Binary File
The arc4 bin file, displayed after pressing the Show Binary File button.

13. Simulation
The ARCTools simulator window after pressing Bin -> Sim.

14. Simulator note.
You need a blank line at the end of the program or the program will not compile with normally a very strange error that makes no sense.

15. ARC example code (1) Example 1 main () { int a=15, b=5,c; c = a+ b; }
.begin
.org 2048
main: ! c = a +b
ld [a], %r1
ld [b], %r2
addcc %r1, %r2, %r3
st %r3, [c]
halt
a: 15
b: 5
c: 0
.end 15

16. ARC Example code (2) Example 2 main() { int a =2, c=0; if (a == 2) {
c =a*4;
} else {
c = a/2; }
.begin
.org 2048
main: ld [a], %r1
!if (a==2)
subcc %r1, 2, %r0
bne else
! true c= a*4
sll %r1, 2, %r1
ba done
! false c = a/2
else: srl %r1, 1, %r1
done: st %r1, [c]
halt
a: 2
c: 0
.end

17. ARC code example (3) Example 3 main () { int a=15, b=5, c;
if (a>=b)
c = a - b;
else
c a + b; }
.begin
.org 2048
main: ld [a], %r1
ld [b], %r2
!if (a>=b)
subcc %r1, %r2, %r3
bneg false
st %r3, [c]
ba done
false: add %r1, %r2, %r3
done: halt
a: 15
b: 5
c: 0
.end 17

18. ARC code example (4) Example 4 main () { int x = 0; while (x <5) {
x = x +1; }
.begin
.org 2048
main: ld [x], %r1
!while (x<5)
top: subcc %r1, 5, %r0
bpos done
!x = x+1
add %r1, 1, %r1
st %r1, [x]
ba top
done: halt
x: 0
.end 18

19. ARC code example (4 modified)
main () {
int x = 0;
while (x <=5) {
x = x +1; }
.begin
.org 2048
main: ld [x], %r1
top: subcc %r1, 5, %r2
subcc %r2, 1, %r0
bpos done
add %r1, 1, %r1
st %r1, [x]
ba top
done: halt
x: 0
.end 19

20. What is the logic to figure out the following
Helpful things to know
What is the logic to figure out the following
If (a>=b) or (a>=1) or any constant
If (a>b) or (a> 1)
If (a < b) or (1 < b)
If (a <= b) or (1 <= b)
If (a==1) or (a==b)
Complex if statements
If ( (a >10) && (b < 10) )

21. ARC code example (5) Example 5 int a=2, b=2, i=1; while (i < 5) {}
Give it a try 21

22. ARC code example (5 cont.)
.begin
.org 2048
main: ld [i], %r1
top: subcc %r1, 5, %r0
bpos done
ld [a], %r2
ld [b], %r3
add %r2, %r3, %r2
st %r2, [a]
add %r1, 1, %r1
st %r1, [i]
ba top
done: halt
a: 2
b: 2
i: 1
.end 22

23. Q A
& 23