W9_2: Jumps and loops
danielroggen
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73 slides
Dec 05, 2017
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About This Presentation
In this unit we explain how jumps and loops can be implemented in assembler on the UoS Educational Processor.
We also explain how for loops constructs expressed in C translate naturally to equivalent assembler constructs.
Unit duration: 50mn.
License: LGPL 2.1
Slide Content
1
Digital Systems and Microprocessor Design
(H7068)
Daniel Roggen
[email protected]
9.2. Jumps and
loops
Digital Systems and Microprocessor Design
(H7068)
Daniel Roggen
[email protected]
9.2. Jumps and
loops
2
Content
•Loops with unconditional jumps
•Conditional jumps
•Conditional loops
•C-style loops to assembler
Content
•Loops with unconditional jumps
•Conditional jumps
•Conditional loops
•C-style loops to assembler
3
Loop with unconditional jump
•Unconditional jumps: changes the value of PC to
destination
–jmp dst
•To do forever a task
–Polling-based event loop
–sensing-actuation loop
•Example:
–Read sensors
–Compute motor speed
–Set motor speed
Loop with unconditional jump
•Unconditional jumps: changes the value of PC to
destination
–jmp dst
•To do forever a task
–Polling-based event loop
–sensing-actuation loop
•Example:
–Read sensors
–Compute motor speed
–Set motor speed
4
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
->00 movra,3h 0 0 0
0
02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
->00 movra,3h 0 0 0
0
02 subra,1h
04 jmp2h
06 ???
5
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 3 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 3 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
6
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 2 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 2 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
7
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 2 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 2 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
8
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 1 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 1 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
9
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 1 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 1 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
10
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 0 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 0 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
11
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 0 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h 0 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
12
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FF 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FF 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
13
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FF 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FF 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
14
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
02 subra,1h
-> 04 jmp2h
06 ???
15
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
-> 02 subra,1h
04 jmp2h
06 ???
16
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
-> 02 subra,1h
04 jmp2h
06 ??? This line is never executed!
Loop with unconditional jump
PCAdrInstr RA RB RC
RD
00 movra,3h FE 0 0
0
-> 02 subra,1h
04 jmp2h
06 ??? This line is never executed!
17
Conditional jumps
•Conditional jumps: changes the value of PC if a condition
is met.
•Condition is tested by checking the flags (carry, zero).
•Flags are set by a prior comparison
•JA:jump if above
–Jumps if Zero=0 and Carry=0
•JB:jump if below
–Jumps if Zero=0 and Carry=1
•JE: jump if equal
–Jumps if Zero=1
•And the opposite: JNA, JNB, JNE (not above, not below,
not equal)
Conditional jumps
•Conditional jumps: changes the value of PC if a condition
is met.
•Condition is tested by checking the flags (carry, zero).
•Flags are set by a prior comparison
•JA:jump if above
–Jumps if Zero=0 and Carry=0
•JB:jump if below
–Jumps if Zero=0 and Carry=1
•JE: jump if equal
–Jumps if Zero=1
•And the opposite: JNA, JNB, JNE (not above, not below,
not equal)
18
Loop with conditional jump (jne)
•Loop with variable from startvalue to 0 (inclusive)
Loop with conditional jump (jne)
•Loop with variable from startvalue to 0 (inclusive)
19
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
->00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
->00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
08 ???
20
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
21
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
22
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
23
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
24
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
25
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
26
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
-> 02 subra,1h
04 cmpra,0h
06 jne02
08 ???
27
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
02 subra,1h
-> 04 cmpra,0h
06 jne02
08 ???
28
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
-> 06 jne02
08 ???
29
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
-> 08 ???
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
-> 08 ???
30
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
-> 08 ???
Program continues execution
Loop with conditional jump (jne)
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0 Z
00 movra,3h
02 subra,1h
04 cmpra,0h
06 jne02
-> 08 ???
Program continues execution
31
C to assembler loops
•In C the syntax for a for loop is:
•for(<initialization>;<condition>; <update>) {code}
•Example: for(i=3; i != 0; i--) {....}
–i will take the value: 3, 2, 1.
•Can be easily translated to assembler
C to assembler loops
•In C the syntax for a for loop is:
•for(<initialization>;<condition>; <update>) {code}
•Example: for(i=3; i != 0; i--) {....}
–i will take the value: 3, 2, 1.
•Can be easily translated to assembler
32
C to assembler loops: alternative 1
•for(<initialization>;<condition>; <update>) {code}
initialization
test:
test condition
if condition then jump to loopcode
jump to endofloop
loopcode:
code
update
jump to test
endofloop:
rest of program
unconditional
conditional
C to assembler loops: alternative 1
•for(<initialization>;<condition>; <update>) {code}
initialization
test:
test condition
if condition then jump to loopcode
jump to endofloop
loopcode:
code
update
jump to test
endofloop:
rest of program
unconditional
conditional
33
C to assembler loops: alternative 2
•for(<initialization>;<condition>; <update>) {code}
initialization
test:
test condition
if not condition then jump to endofloop
code
update
jump to test
endofloop:
rest of program
unconditional
conditional
This requires to negate the condition!
Processors usually provide conditional jumps if condition (je,ja,jb)
and conditional jumps if not condition (jne,jna,jnb)
C to assembler loops: alternative 2
•for(<initialization>;<condition>; <update>) {code}
initialization
test:
test condition
if not condition then jump to endofloop
code
update
jump to test
endofloop:
rest of program
unconditional
conditional
This requires to negate the condition!
Processors usually provide conditional jumps if condition (je,ja,jb)
and conditional jumps if not condition (jne,jna,jnb)
34
C to assembler loops
•With alternative 1 the conditional jump is to a nearby
address (instruction skip)
•Alternative 2 leads to more compact code
•Some processors have "relative jumps" that allow to
change PC by an offset
–On Intel/AMD x86 the "short relative jump" allows to offset PC by
up to -128 to +127 bytes
•What happens on x86 if the loop code is longer than 127
bytes?
–Alternative 2 cannot be used with short relative jump!
–Alternative 1 must be used
Programming influenced by processor architecture!
That is why higher level languages (e.g. C) and compilers are
used: they can optimize the code
Programming influenced by processor architecture!
Higher level languages (e.g. C) and compilers allow to select the
right assembler construct to optimize the code
C to assembler loops
•With alternative 1 the conditional jump is to a nearby
address (instruction skip)
•Alternative 2 leads to more compact code
•Some processors have "relative jumps" that allow to
change PC by an offset
–On Intel/AMD x86 the "short relative jump" allows to offset PC by
up to -128 to +127 bytes
•What happens on x86 if the loop code is longer than 127
bytes?
–Alternative 2 cannot be used with short relative jump!
–Alternative 1 must be used
Programming influenced by processor architecture!
That is why higher level languages (e.g. C) and compilers are
used: they can optimize the code
Programming influenced by processor architecture!
Higher level languages (e.g. C) and compilers allow to select the
right assembler construct to optimize the code
35
C to assembler loops
•for(i=3; i != 0; i--) {....}
•Alternative 2
C to assembler loops
•for(i=3; i != 0; i--) {....}
•Alternative 2
36
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
->00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
->00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
37
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
38
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
39
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
40
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
41
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
42
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
43
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
44
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
45
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
46
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
47
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
48
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
49
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
-> 06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
50
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
-> 0A subra,1h
0C jmp02
0E ???
51
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
-> 0C jmp02
0E ???
52
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,3h
-> 02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
53
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
-> 04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
0E ???
54
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
-> 0E ???
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
-> 0E ???
55
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
-> 0E ???
Program continues execution
for(i=3; i != 0; i--) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0 Z
00 movra,3h
02 cmpra,0h
04 je0eh
06 ...
08 ...
0A subra,1h
0C jmp02
-> 0E ???
Program continues execution
56
C to assembler loops
•for(i=3; i != 0; i--) {....}
•Alternative 1
->00 movra,3h
02 cmpra,0h
04 jne08h
06 jmp0E
08 ...
0A subra,1h
0C jmp02
0E ???
C to assembler loops
•for(i=3; i != 0; i--) {....}
•Alternative 1
->00 movra,3h
02 cmpra,0h
04 jne08h
06 jmp0E
08 ...
0A subra,1h
0C jmp02
0E ???
57
C to assembler loops
•for(i=0; i <3; i++) {....}
–i takes the values: 0, 1, 2
•Alternative 1
C to assembler loops
•for(i=0; i <3; i++) {....}
–i takes the values: 0, 1, 2
•Alternative 1
58
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
-> 00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
-> 00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
59
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
60
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
61
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
-> 08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
-> 08 ...
0A addra,1h
0C jmp02
0E ???
62
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
-> 0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
0 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
-> 0A addra,1h
0C jmp02
0E ???
63
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
-> 0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
-> 0C jmp02
0E ???
64
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
65
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
fast forw
ard som
e steps...
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
1 0 0 0
C
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
fast forw
ard som
e steps...
66
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
-> 0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
2 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
-> 0A addra,1h
0C jmp02
0E ???
67
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
-> 0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
C
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
-> 0C jmp02
0E ???
68
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
C
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0
C
00 movra,0h
-> 02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
69
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
-> 04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
70
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
-> 06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
-> 06 jmp0E
08 ...
0A addra,1h
0C jmp02
0E ???
71
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
-> 0E ???
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
-> 0E ???
72
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
-> 0E ???
Program continues execution
for(i=0; i <3; i++) {....}
PCAdrInstr RA RB RC RD
FLAGS
3 0 0 0 Z
00 movra,0h
02 cmpra,3h
04 jb08h
06 jmp0E
08 ...
0A addra,1h
0C jmp02
-> 0E ???
Program continues execution
73
Summary
•Basic loop constructs can be realized in assembler
•Pay attention to the desired range of values of the
variables and where the test is placed!
•The "C to assembler" examples generalize to more
complex tests!
–for(i=0; (i<100) && (obstacle1==0); i++) {....}
–Use boolean logic to combine multiple simple tests together
–Or test individual parts and have several conditional jumps
•Knowledge sufficient to complete the coursework
assignment involving programming
Summary
•Basic loop constructs can be realized in assembler
•Pay attention to the desired range of values of the
variables and where the test is placed!
•The "C to assembler" examples generalize to more
complex tests!
–for(i=0; (i<100) && (obstacle1==0); i++) {....}
–Use boolean logic to combine multiple simple tests together
–Or test individual parts and have several conditional jumps
•Knowledge sufficient to complete the coursework
assignment involving programming
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