ELM333 µ-processor Final 2013 student
name :
1. Write an ARM code to perform the following.
r4 =r0 +64r1
Assume that the integers are signed.
2. What does the following ARM code performs?
mov r4, #10
mov r5, #1
LOOP: mul r5, r5, r4
subs r4, r4, #1
bgt LOOP
3. What does the following ARM code performs?
mov r4, #0x2FC0 0000
mov r5, #7
mov r0, #1
LOOP: ldr r1, [r4, r5, LSL#2]
mul r0, r0, r1
subs r5, r5, #1
bge LOOP
4. What does the following ARM code performs?
mov r4, #0x2FC0 0000
mov r5, #7
mov r0, #0
LOOP: str r0, [r4, r5, LSL#2]
subs r5, r5, #1
bge LOOP
5. Write the C code equivalent of the ARM code.
cmp r4,#16
ble END
add r0, r0,#5
END:
if( ){
}
6. Let xbe a global variable stored at a direct
address and let ybe a local variable stored at
the address that is 8 byte higher than the stack
pointer. Which one of the codes below may load
xand which one may load y?
mov r4, 0x2F000000
ldr r1, [r4] ldr r0, [r13, #8]
7. Let the stack pointer r13=0xA0000000. Write
the ARM memory instructions loading the stack
variables x,y, and zto the registers r0,r1, and
r2 respectively.
0xA0000000
0xA0000004
0xA0000008
0xA000000C x
0xA0000010 y
0xA0000014 z
8. How do the following code change the pins of
the 8 bit I/O port whose data register at the
address 0x40005120?
*(char *)0x40005120 &= 0x0F
*(char *)0x40005120 |= 0x0F
9. The below code sets first I/O pin 0 and a few
cycles later sets I/O pin 1.
*(char *)0x40005120 |= 1
*(char *)0x40005120 |= 2
However, the optimization replaces this code
with *(char *)0x40005120 |= 3. Which key-
word must be used to prevent the optimization.
*(keyword char *)0x40005120 |= 1
*(keyword char *)0x40005120 |= 2
C keywords
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
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